Foundations IV

• Three sequential steps: chromosomal sex (fertilization) → gonadal sex (weeks 6–9) → phenotypic sex (weeks 9–12). The gonad is indifferent until week 6, and both duct systems are present in every embryo — mesonephric (Wolffian) and paramesonephric (Müllerian).
• SRY on the short arm of the Y is the master switch. Present → testis. Absent → WNT4 / RSPO1 / β-catenin and FOXL2 drive ovarian differentiation; primitive sex cords degenerate, cortical cords break up into primordial follicles around the oogonia.
• Female development is decided by two absences, not by an ovarian hormone. No Sertoli cells → no anti-Müllerian hormone → paramesonephric ducts persist. No Leydig cells → no testosterone → mesonephric ducts regress. No DHT → external genitalia stay feminine.
• Paramesonephric derivatives: cranial unfused portions → fallopian tubes; fused caudal portions → uterovaginal canal → uterus and upper vagina.
• The vagina has two origins. Upper from the fused paramesonephric ducts; lower from the sinovaginal bulbs of the urogenital sinus, which form the vaginal plate that canalizes. The hymen marks the junction.
• External genitalia, all without androgen exposure: genital tubercle → clitoris; urogenital folds → labia minora; labioscrotal swellings → labia majora.

Nearly every uterine and vaginal anomaly is a failure of one of three steps: fusion, canalization, or resorption of the septum.

• Oogonia complete mitosis and enter meiosis I by month 5 of fetal life; germ cell mitosis then ceases and no additional oocytes are ever formed.
• The numbers: ~1–2 million primary oocytes at birth → ~300,000 at puberty → only 400–500 ever ovulate across a reproductive life → essentially none at menopause. Everything else becomes atretic.
• Meiosis I is arrested in prophase I from fetal life until the LH surge that ovulates that particular oocyte — an arrest that can last 50 years. Meiosis II arrests at metaphase II and completes only if fertilization occurs.

Adrenarche is one of the three critical endocrine changes of puberty.

• Three critical endocrine changes at puberty: (1) adrenarche, (2) decreased gonadostat sensitivity, and (3) development of a positive feedback system between gonadotropins and GnRH. Adrenarche is defined there as the increased production of adrenal androgens, occurring in both sexes.
• The line to quote: adrenarche and gonadarche are overlapping but independent developmental processes — adrenarche may occur without gonadarche, and vice versa. That single sentence is the whole objective.
• Adrenarche is an adrenal event, not an HPG event. The zona reticularis matures from about age 6–8, raising 17,20-lyase activity and lowering 3β-HSD, which shifts output toward DHEA and DHEAS.
• What it produces: pubarche (pubic and axillary hair), adult body odor, mild acne, slight growth acceleration.
• What it does not produce: breast development, a true growth spurt, or any rise in LH/FSH. Those require gonadarche — reactivation of the HPG axis.
• Premature adrenarche = these signs before age 8 in a girl with no thelarche and normal growth velocity. Usually benign.

• Sequence in girls: thelarche → pubarche → peak height velocity → menarche. Note the order: in girls the growth spurt comes BEFORE menarche — the opposite of boys, where it is late.
• Timing: gonadotropin secretion begins rising around age 8; puberty and menstruation usually fall between 10 and 14 years, average 12. Menarche follows thelarche by roughly 2–2.5 years.
• The axis is competent in infancy but silent in childhood. the hypothalamus can secrete GnRH but lacks the signal to do so; puberty is initiated by a maturation process elsewhere in the brain, likely the limbic system. Puberty is disinhibition, not new machinery.
• Pulsatility is everything. GnRH is released in pulses of 5–25 minutes every 1–2 hours from the arcuate nucleus of the mediobasal hypothalamus, driving LH pulses about every 90 minutes.
• Continuous GnRH abolishes the response. when GnRH is infused continuously rather than in pulses, its ability to cause release of LH and FSH by the anterior pituitary is lost.
• The last thing to mature is positive feedback. The first cycles after menarche are typically anovulatory because the preovulatory LH surge is not yet of sufficient magnitude — no surge, no corpus luteum, no progesterone phase.

• Both paths shorten adult height. Sex steroids advance skeletal maturation faster than linear growth, so epiphyses fuse early — a tall child who becomes a short adult.
• Delayed puberty: no thelarche by 13, or no menarche by 15. Measure LH/FSH first — it splits the differential in two.
• High FSH/LH (hypergonadotropic) = the gonad has failed, so negative feedback is gone. Classic: Turner syndrome, 45,X.
• Low or normal FSH/LH (hypogonadotropic) = the axis is not driving. Constitutional delay (commonest, family history, delayed bone age), functional suppression (energy deficit, athletics, anorexia, chronic illness), Kallmann syndrome (with anosmia), pituitary lesion.

• Two clocks run together: the ovarian cycle (follicular → ovulation → luteal) and the endometrial cycle (menstrual → proliferative → secretory). The ovary drives; the endometrium responds.
• Early follicular. The dying corpus luteum stops making estrogen, progesterone and inhibin, which releases the pituitary from negative feedback → FSH rises → 6–12 primary follicles are recruited.
• Two cells, two gonadotropins. LH → theca cells → androgens (androstenedione, testosterone) — but the theca lacks aromatase. The androgens diffuse into the granulosa, where FSH-stimulated aromatase converts them to estradiol. Neither cell can make estrogen alone.
• Selection of the dominant follicle. Estradiol from the fastest-growing follicle suppresses pituitary FSH, starving the other 5–11 into atresia. The dominant follicle survives falling FSH because estrogen upregulated its own FSH receptors — a local positive feedback that the others lack.
• The feedback flip. Sustained high estradiol switches feedback from negative to positive, producing an LH surge that rises 6- to 10-fold and peaks about 16 hours before ovulation.
• Ovulation needs two mechanical events, both LH-triggered: (1) the theca externa releases proteolytic enzymes (collagenase) that weaken the follicular capsule, and (2) new vessels and prostaglandins cause hyperemia and plasma transudation → the follicle swells and the stigma degenerates → rupture.
• Luteal phase. Granulosa and theca interna cells luteinize; the corpus luteum peaks at 7–8 days and involutes at 12 days, becoming the corpus albicans. Progesterone dominates. Progesterone + estrogen + inhibin suppress FSH and LH.
• Rescue or withdrawal. No fertilization → no hCG → the corpus luteum involutes → hormone withdrawal → menstruation, and the released pituitary starts the next cycle. Fertilization → placental hCG acts like LH and maintains the corpus luteum for the first 2–4 months.

• The mechanism of menstruation, in order: progesterone withdrawal → endometrium involutes to ~65% of its thickness → in the 24 hours before onset the tortuous vessels become vasospastic, probably via vasoconstrictor prostaglandins → ischemic necrosis → the superficial layers desquamate over ~48 hours → prostaglandin-driven uterine contractions expel the contents.
• The basalis is spared because it is supplied by straight basal arteries not subject to the spiral-artery spasm — which is why it can regenerate the functionalis each month.
• Volume and clotting: ~40 mL blood plus ~35 mL serous fluid. Menstrual blood is normally non-clotting because a fibrinolysin is released with the necrotic endometrium; heavy flow can outstrip the fibrinolysin, which is why clots signal heavy bleeding.
• Cervical mucus is part of the cycle: under estrogen it becomes thin and stringy and aligns along the cervical canal to guide sperm.

Every one of these is the cycle you just learned, broken at a named point. Reason from which part of the loop failed, not from the symptom.

• Amenorrhea — work it as five compartments, in order. (1) Pregnancy, always, first. (2) Outflow tract — Müllerian anomaly, imperforate hymen, Asherman syndrome. (3) Ovary — FSH HIGH, because a failed gonad cannot feed back (primary ovarian insufficiency, Turner). (4) Pituitary/hypothalamus — FSH LOW or normal (functional hypothalamic amenorrhea from energy deficit or athletics, hyperprolactinemia, Sheehan). (5) Other endocrine — thyroid disease, PCOS.
• The one lab that splits the differential in half is FSH. High = the ovary. Low or normal = everything above it. This is the same maneuver as delayed puberty, because it is the same axis.
• The version of this: when the ovaries secrete small quantities of estrogen — in hypogonadism or as a result of other factors such as hypothyroidism — the cycle fails, months may elapse between periods, or menstruation may cease altogether. He also notes prolonged cycles are frequently associated with failure of ovulation from insufficient LH surge.
• Primary dysmenorrhea is a prostaglandin disease. The secretory endometrium generates PGF2α, which drives myometrial contraction and uterine ischemia. Exactly this substrate: vasoconstrictor prostaglandins "present in abundance at menstruation, whose contractile effects initiate uterine contractions that expel the uterine contents."
• Why primary dysmenorrhea starts 6–12 months AFTER menarche, not at it: it needs ovulatory cycles. Progesterone from a corpus luteum primes the endometrium to make PGF2α — and the first cycles are anovulatory. If painful periods begin years later and worsen, think secondary dysmenorrhea: endometriosis, adenomyosis, fibroids.
• Anovulatory (dysfunctional) bleeding — the highest-yield chain in this lecture: no ovulation → no corpus luteum → no progesterone → estrogen unopposed → the endometrium proliferates past its blood supply with no progesterone-driven stromal support → it breaks down erratically. Irregular, unpredictable, sometimes heavy. This is PCOS, perimenopause, and the first years after menarche.
• Luteal phase defect — a short (<10 day) or hormonally inadequate luteal phase gives insufficient secretory transformation, so the endometrium is out of phase with the embryo.

• Estrogen = proliferation. At puberty output rises 20-fold or more; ovaries, tubes, uterus and vagina all enlarge several times.
• The vaginal epithelium changes class: estrogen converts it from cuboidal to stratified, considerably more resistant to trauma and infection. Losing estrogen at menopause reverses this — that is atrophic vaginitis in one sentence.
• Estrogen on the tube: more ciliated epithelial cells and enhanced ciliary activity, always beating toward the uterus.
• Estrogen on bone: inhibits osteoclastic activity, partly via osteoprotegerin (osteoclastogenesis inhibitory factor), and closes the epiphyses — a stronger effect than testosterone's, which is why female growth ceases earlier.
• Progesterone = secretion and quiescence. Secretory transformation of the endometrium; decreases the frequency and intensity of uterine contractions, preventing expulsion of an implanted ovum; increases tubal secretion to nourish the dividing ovum; develops breast lobules and alveoli (but does not cause milk secretion — that needs prolactin).
• SERMs are tissue-selective because the receptor-ligand complex recruits different coactivators and corepressors in different tissues. Tamoxifen: antagonist in breast, agonist in endometrium (hence hyperplasia and carcinoma risk) and bone. Raloxifene: antagonist in breast and endometrium, agonist in bone — which is why it treats osteoporosis without the endometrial risk.

• Definitions. Menopause = 12 consecutive months of amenorrhea with no other cause, dated retrospectively to the final menstrual period; median ~51. Perimenopause begins with persistent cycle-length variation of ≥7 days and ends 12 months after the FMP. Postmenopause follows. Premature = before 40; early = 40–45.
• The mechanism is depletion. "burning out" of the ovaries: by ~45 only a few primordial follicles remain, estrogen production falls toward zero, and when it drops below a critical value it can no longer inhibit FSH and LH — so gonadotropins rise continuously and in large quantities, mainly FSH.
• Order of change — and estradiol is not first. Fewer follicles → inhibin B falls first → FSH rises while estradiol is still normal or even high, because the higher FSH recruits follicles faster. That shortened follicular phase is why cycles shorten early in the transition and lengthen later when too few follicles remain.
• After menopause the dominant estrogen is estrone, from peripheral aromatization of adrenal androstenedione in adipose tissue — not ovarian estradiol.
• Symptoms hot flushes with extreme skin flushing, psychic sensations of dyspnea, irritability, fatigue, anxiety, and decreased strength and calcification of bones; severe enough to warrant treatment in about 15% of women.

The pattern changes in a predictable order. Recognizing the stage matters because the bleeding risk is not the same at each one.

One cause, six organ systems. Every row below traces back to loss of estrogen — which is what makes this objective answerable from a single mechanism rather than a list.

• All three arise from intermediate mesoderm, cranial to caudal, in time order.
• Pronephros — cervical region, week 4, vestigial and entirely regressed.
• Mesonephros — thoracolumbar, functions transiently. Its duct, the mesonephric (Wolffian) duct, persists and is the origin of the ureteric bud.
• Metanephros = the definitive kidney, week 5, from two tissues that must induce each other:
  • Ureteric bud (an outgrowth of the mesonephric duct) → ureter, renal pelvis, major and minor calyces, collecting ducts.
  • Metanephric blastema → the nephron proper, glomerulus through distal tubule.
• The induction is reciprocal. GDNF from the blastema drives ureteric bud branching; the bud in turn induces the blastema to differentiate. Neither tissue develops alone — which is exactly why a bud that fails to reach or branch produces renal agenesis or multicystic dysplastic kidney.
• Ascent and rotation. The kidney starts in the pelvis and ascends as body curvature diminishes, passing through the fork of the umbilical arteries.

• Same logic as the female tract, but with the hormones present. SRY → testis → two cell types, two hormones, two jobs.
• Sertoli cells → anti-Müllerian hormone → the paramesonephric ducts regress.
• Leydig cells → testosterone → the mesonephric ducts persist → epididymis, ductus deferens, seminal vesicle, ejaculatory duct.
• DHT (testosterone via 5α-reductase) → prostate, penis, scrotum, and closure of the urethral folds.
• Descent: the gubernaculum guides the testis; the processus vaginalis, an evagination of peritoneum, precedes it through the inguinal canal. The reflected fold becomes the visceral and parietal layers of the tunica vaginalis; the connecting canal normally obliterates at or shortly after birth.
• 97% of male newborns have both testes in the scrotum before birth; most of the rest descend in the first 3 months. Cryptorchidism in ~1%, associated with a 3–5% incidence of renal anomalies.

• The path of urine: collecting duct → papilla → minor calyx → major calyx → renal pelvis → ureter → bladder → urethra.
• Each kidney weighs about 150 g, sits retroperitoneally, and has a hilum transmitting renal artery, vein, lymphatics, nerves and ureter. Cortex outside, medulla inside; the medulla forms 8–10 renal pyramids.
• Urine transport is active, not gravitational. The calyces, pelvis and ureter contain contractile elements that propel urine toward the bladder.
• Arterial order — worth memorizing as a chain: renal artery → interlobar → arcuate → interlobular (radial) → afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries → venous system in reverse.
• Renal blood flow is ~1100 mL/min, about 22% of cardiac output — enormous for two organs weighing 300 g, because the flow is for filtration, not for the kidney's own metabolism.

All from

• 800,000–1,000,000 nephrons per kidney, and the kidney cannot regenerate them. After age 40 the number falls ~10% per decade — so at 80 many people have 40% fewer than at 40.
• Segments in order: glomerulus in Bowman's capsule → proximal tubule (cortex) → loop of Henle (thin descending, thin ascending, thick ascending) → macula densa → distal tubule → connecting tubule → cortical collecting duct → medullary collecting duct.
• The macula densa sits at the end of the thick ascending limb, in contact with its own glomerulus — the anatomical basis of tubuloglomerular feedback.

• A stone needs three things to go wrong: supersaturation (high solute load or low urine volume), an unfavourable pH, and loss of inhibitors (citrate, magnesium).
• The worked mechanism is hyperparathyroidism. Excess PTH mobilizes calcium and phosphate from bone and raises intestinal absorption; all of it must be excreted, so urinary calcium and phosphate rise proportionally until calcium phosphate precipitates. Calcium oxalate also forms, because even normal oxalate levels precipitate at high calcium.
• The pH lever. most renal stones are poorly soluble in alkaline media, so stone formation is considerably more likely in alkaline urine — which is why acidotic diets and acidic drugs were used to treat renal calculi.
• kidney stones at , including struvite stones from urea-splitting bacteria. That statement is true for calcium phosphate and struvite. Uric acid and cystine are the reverse — they precipitate in acid urine and are treated by alkalinization with potassium citrate. Do not over-generalize the sentence.
• Stones as a cause of postrenal AKI — obstruction anywhere from calyx to bladder outflow, from precipitated calcium, urate or cystine.

Both are named in this lecture's outline but neither gets its own objective — which usually means they are quiz fodder rather than essay material. Pyelonephritis; hydronephrosis appears nowhere in your three books.

• Pyelonephritis is ascending infection, usually E. Coli from the bladder up the ureter into the renal pelvis and parenchyma. Among the infections causing interstitial nephritis and lists it in his table of causes of chronic kidney disease.
• Why the medulla suffers first — acute pyelonephritis at and chronic at . The mechanism — it is relatively hypoxic (the vasa recta are countercurrent), hypertonic, and has poor complement activity, so it defends against bacteria worse than the cortex does.
• Clinically: fever, flank pain, CVA tenderness plus lower-tract symptoms. WBC casts are the finding that proves renal parenchymal involvement rather than bladder infection — casts can only form in tubules.
• Repeated or chronic pyelonephritis scars the interstitium, and because nephrons cannot be replaced, that scarring is a permanent step toward chronic kidney disease — the "vicious cycle."
• Hydronephrosis is a pressure disease, not an infection. exactly: "retrograde increases in hydrostatic pressure involving the renal pelvis and calyces produce hydronephrosis," and "acute, complete obstructions cause an increase in pressure that is transmitted to the proximal tubule and decreases glomerular filtration" — to zero if obstruction is complete. Obstruction anywhere from calyx to urethra raises pressure retrograde → the collecting system dilates → the medulla is compressed. Concentrating ability is lost first (the medullary gradient is the most pressure-sensitive function), then GFR falls as back-pressure opposes filtration.
• You the frame for it even without the word: postrenal AKI from obstruction of the urinary collecting system anywhere from the calyces to the outflow from the bladder, most commonly kidney stones.

Framework from

Listed in this lecture's outline as normal anatomy of the endocrine system. Worth having as one list, because later lectures assume it.

Listed in this lecture's outline as terminology of endocrinology. These words are how exam stems are phrased, so misreading one costs the question regardless of what you know.

• Architecture 1 — the axis. Hypothalamic releasing hormone → anterior pituitary trophic hormone → peripheral gland hormone, with long-loop negative feedback from the target hormone onto both upper levels and short-loop feedback from the pituitary hormone onto the hypothalamus.
• Architecture 2 — direct feedback on a non-hormonal variable. No pituitary at all: the gland senses the variable itself. PTH senses calcium; insulin senses glucose; ADH senses osmolality. This is the category PTH belongs to.
• Architecture 3 — neuroendocrine. The adrenal medulla is a modified sympathetic ganglion driven by preganglionic fibers. The posterior pituitary stores hormones it does not make: ADH and oxytocin are synthesized in hypothalamic neurons and travel down axons.
• The anterior pituitary has no such neural connection — it is reached by the hypothalamic-hypophysial portal vessels, a private circulation, not the systemic blood.
• Also worth naming: paracrine (acts on neighbouring cells) and autocrine (acts on the secreting cell itself).

• Suspect too much → try to suppress it. Suspect too little → try to stimulate it. A normal gland obeys; a pathological one does not. That single sentence generates most endocrine testing.
• Suppression tests: dexamethasone suppression for Cushing syndrome; oral glucose tolerance for acromegaly (GH should suppress and doesn't); saline suppression for primary aldosteronism.
• Stimulation tests: cosyntropin (ACTH) stimulation for adrenal insufficiency; GnRH stimulation to separate central from peripheral precocious puberty; insulin tolerance test for GH and ACTH reserve.
• Free vs total. Total hormone tracks binding protein, not activity. Pregnancy and estrogen raise TBG, so total T4 rises while free T4 and the patient are normal. Same logic for calcium: correct for albumin, or measure ionized calcium.
• Timing and pulsatility. Cortisol has a diurnal rhythm; GH, LH and PTH are pulsatile. A single random level can be meaningless — which is why 24-hour collections, midnight salivary cortisol, and dynamic testing exist.
• The measurement side — hormone concentrations are assayed by immunoassay.

Also in parathyroid glands (structure and function), hyperparathyroidism, hypoparathyroidism .

• Four glands, immediately behind the upper and lower poles of the thyroid, each ~6 × 3 × 2 mm and looking like dark brown fat. They are hard to find at surgery because they often look like just another lobule of the thyroid gland.
• Chief cells secrete PTH. Oxyphil cells are present in adults and their function is uncertain — probably depleted chief cells.
• Synthesis chain: preprohormone 110 aa → prohormone 90 aa → hormone 84 aa, packaged in secretory granules.
• Why assays say "intact PTH": the kidney clears the whole 84-aa hormone within minutes but fails to clear many fragments for hours, so a large share of measured activity is fragments.
• Regulation is direct, by ionized calcium, through the calcium-sensing receptor (CaSR) on the chief cell. No trophic pituitary hormone is involved — this is Architecture 2 from the section above, and it is one of the fastest loops in the body.
• Magnesium cuts both ways. Moderate hypomagnesemia stimulates PTH; severe hypomagnesemia blocks PTH release, producing functional hypoparathyroidism — which is why hypocalcemia that will not correct with calcium needs magnesium.

One sentence to hang it on: PTH raises calcium and drops phosphate.

• Bone, rapid phase (minutes–hours): osteolysis. The osteocytic membrane system — osteocytes and osteoblasts connected by processes throughout bone — separates bone fluid from ECF and pumps calcium out of it. PTH activates that pump, releasing calcium phosphate salts without resorbing the matrix.
• Bone, slow phase (days–weeks): osteoclastic resorption, which does destroy matrix.
• Kidney: increases calcium reabsorption (thick ascending limb and distal tubule) and decreases phosphate reabsorption (proximal tubule) → phosphaturia.
• Intestine: indirect. PTH stimulates renal 1α-hydroxylase → calcitriol → calbindin in intestinal epithelium → calcium absorption. Note the calbindin effect takes about 2 days to develop and persists for weeks.

• Secondary precisely: high levels of PTH occur as a compensation for hypocalcemia rather than as a primary abnormality of the parathyroid glands. In CKD the chain is failed 1α-hydroxylation → low calcitriol → low calcium absorption, plus phosphate retention.
• Why mild primary disease presents as stones, not bones. patients with mild hyperparathyroidism show few signs of bone disease but have an extreme tendency to form kidney stones, because the mobilized and absorbed calcium and phosphate must be excreted, raising urinary concentrations until calcium phosphate precipitates.
• Severe chronic disease → osteoclastic resorption → weakened bone, cavities filled with multinucleated osteoclasts (osteitis fibrosa cystica).
• The danger line: calcium above about 17 mg/dL risks "parathyroid poisoning," with death possible in a few days.

• Commonest cause is surgical, and exactly why: before the glands' importance was recognized, total or subtotal thyroidectomy frequently resulted in removal of the parathyroid glands as well.
• There is real reserve. Removing half the glands usually causes no abnormality; removing three of four causes only transient hypoparathyroidism, because remaining tissue hypertrophies.
• Labs: LOW calcium, HIGH phosphate, LOW PTH — the mirror image of primary hyperparathyroidism.
• Symptoms are neuromuscular irritability from hypocalcemia: perioral numbness, paresthesia, carpopedal spasm, Chvostek and Trousseau signs, laryngospasm, seizures, and a prolonged QT. The tetany but not the eponyms.
• Pseudohypoparathyroidism is end-organ resistance to PTH: low calcium and high phosphate like hypoparathyroidism, but PTH is HIGH. The PTH level is the only thing that separates them.

• Three layers: perimetrium (peritoneal serosa), myometrium (thick smooth muscle, arranged in figures of eight around the vessels — which is what makes post-partum contraction hemostatic), and endometrium (functionalis + basalis).
• Parts: fundus, body, isthmus, cervix. The uterine cavity is continuous with the tubes above and the cervical canal below.
• Normal position is anteverted and anteflexed — the whole uterus tips forward on the vagina (anteversion) and the body bends forward on the cervix (anteflexion). It rests on the bladder.
• Supports, in order of importance — this is examinable and counter-intuitive: the pelvic diaphragm (levator ani) and perineal body do the real work; the transverse cervical (cardinal) and uterosacral ligaments anchor the cervix; the round ligament maintains anteversion but is not a major support; the broad ligament is a peritoneal fold, not a ligament at all.
• The cervix has two epithelia and that is the whole point. "the point at which the columnar epithelium of the cervix meets the squamous epithelium of the vagina is called the transformation zone, or the squamous-columnar junction," and it "is the usual site of cervical dysplasia or carcinoma in situ." Endocervix = simple columnar, mucus-secreting. Ectocervix = stratified squamous, continuous with the vagina. Where they meet is the squamocolumnar junction; the zone of active metaplasia between the original and current junction is the transformation zone.
• Cervical mucus is cyclical: under estrogen it becomes thin and stringy and aligns along the canal to guide sperm; progesterone makes it thick and hostile.

Older material calls this dysfunctional uterine bleeding (DUB); the current scheme is PALM-COEIN, which exists because "menorrhagia" and "metrorrhagia" meant different things to different clinicians. Frames AUB by pattern (heavy menstrual, intermenstrual) and etiology.

• Describe bleeding by four axes, not by old eponyms: frequency, regularity, duration, volume. "Heavy menstrual bleeding" replaced menorrhagia; "intermenstrual bleeding" replaced metrorrhagia.
• The commonest COEIN entry by far is O — ovulatory dysfunction, and you already know its mechanism from WH 1: no corpus luteum → no progesterone → unopposed estrogen → erratic breakdown.
• the six evaluation goals, including "identifying risk of medical conditions that may impact bleeding (eg, inherited bleeding disorders, endocrine disease)" and "assessing the contribution of medications, including hormonal contraceptives, anticoagulants, and natural product supplements."
• Coagulopathy is under-diagnosed: up to 20% of adolescents with heavy menstrual bleeding have an underlying bleeding disorder, most often von Willebrand disease.

• The definition: leiomyomas are "benign tumors that develop from smooth muscle cells in the myometrium," and are the most common benign tumors of the uterus; most remain small and asymptomatic. Prevalence rises between 30 and 50 and decreases with menopause; myomas develop in about 30% of white and 50% of Black women by age 50, with incidence in Black and Asian women 2–5× higher.
• On examination, irregular, NONTENDER nodularity of the uterus on bimanual exam, confirmed by sonography or MRI.
• Leiomyoma (fibroid) — a benign monoclonal tumor of myometrial smooth muscle, each arising from a single cell, which is why a uterus can hold many fibroids of different sizes. Estrogen- and progesterone-dependent: they grow through reproductive life and regress after menopause. The commonest tumor of the female pelvis.
• Location determines the symptom — this is the examinable part:
  • Submucosal — distorts the cavity → heavy bleeding and infertility, out of proportion to size
  • Intramural — within the wall → bulk symptoms, bleeding
  • Subserosal — outward → pressure on bladder or bowel; may be pedunculated and can torse
• Degeneration when a fibroid outgrows its blood supply: hyaline (commonest), red (carneous) degeneration in pregnancy causing acute pain, cystic, calcific.
• Adenomyosis — "the presence of endometrial glands and stroma within the uterine myometrium." On bimanual exam the uterus is diffusely enlarged, globular, and most tender just before or after menstruation, with secondary dysmenorrhea that worsens as disease progresses. Is unresponsive to hormone treatment. The classic picture is a diffusely enlarged, globular, tender uterus in a multiparous woman in her 40s, with heavy bleeding and dysmenorrhea.

Complete moles are 46,XX (85%), of paternal origin with no evidence of a fetus; partial moles show an embryo or gestational sac, are triploid, slower-growing, and "often present clinically as spontaneous pregnancy loss"; and partial moles tend to follow a benign course, while complete moles have a greater tendency to become choriocarcinoma — which develops in 2–3%. Also. GTD nowhere.

• the essentials of diagnosis: amenorrhea, irregular uterine bleeding beginning at 6–16 weeks, serum β-hCG >40,000 mIU/mL, passage of grapelike clusters of enlarged edematous villi, and ultrasound showing a heterogeneous echogenic image with no fetus or placenta.
• Frequency 1:1500 pregnancies in North America, highest in Asian patients; risk factors are prior pregnancy loss, prior mole, and age under 21 or over 35. About 10% need further treatment after evacuation.
• Bilaterally enlarged cystic ovaries may be palpable — them to "ovarian hyperstimulation due to excess β-hCG," and notes preeclampsia-eclampsia may develop in the second trimester of an untreated mole.

HPV infection accounted for 75% of CIN cases in a 1000-woman case-control study, caused 80% of cervical cancers, and is implicated in almost all cases of CIN; also that about one in eight young women will have cervical dysplasia by age 20. The molecular mechanism: "E6 binds to p53… and promote[s] its degradation; E7 binds and inactivates p53 and Rb proteins," with progression to HSIL.

• HPV infects the basal cells of the transformation zone through a micro-abrasion. Most infections are transient and cleared within 1–2 years — transient infection is not disease.
• The word that matters in the objective is "persistent." Only infection that persists allows the viral genome to integrate into host DNA, and integration disrupts the viral E2 gene, which normally represses E6 and E7.
• E6 degrades p53 (loses apoptosis and the G1 damage checkpoint). E7 inactivates Rb (releases E2F, driving unchecked S-phase entry). Two tumor suppressors down at once — that is why HPV is oncogenic and why the high-risk types (16 and 18, ~70% of cervical cancer) differ from low-risk types (6 and 11 → warts, no integration).
• The progression is slow and reversible early: infection → CIN 1 (mostly regresses) → CIN 2 → CIN 3 → invasive carcinoma, typically over 10–20 years. That long window is the entire reason screening works.
• Screening — and note the two guidelines disagree. one set of recommendations begins screening at age 21, while the American Cancer Society recommends primary HPV testing every 5 years beginning at age 25. If a stem asks a starting age, the answer depends on whose guideline — say which you are using.
• Cofactors that favor persistence: smoking, immunosuppression (HIV), high parity, long-term oral contraceptive use.

• Ovary: suspended by the suspensory ligament of the ovary (carrying the ovarian vessels — the pedicle that twists in torsion) and the ligament of the ovary to the uterus. It is the one intraperitoneal pelvic organ with no peritoneal covering — the ovulated oocyte is released into the peritoneal cavity.
• Ovarian arteries arise from the abdominal aorta (not the internal iliac) because the gonad developed high and descended — the venous drainage is asymmetric for the same reason: right ovarian vein → IVC, left ovarian vein → left renal vein.
• Vagina: a fibromuscular tube with rugae, related anteriorly to bladder and urethra, posteriorly to rectum and the rectouterine pouch. The fornices surround the cervix.
• Vaginal mucosa is non-keratinized stratified squamous with NO glands — lubrication comes from cervical mucus, transudate, and the greater vestibular (Bartholin) glands.
• The estrogen–glycogen–lactobacillus–pH axis — vaginal defenses "are greatest when estrogen levels are high and the vagina contains a normal population of Lactobacillus acidophilus… Any condition that causes vaginal pH to rise, such as douching, low estrogen levels, or destruction of L. Acidophilus by antibiotics, lowers vaginal defenses against infection.": estrogen loads the epithelium with glycogen → lactobacilli ferment it to lactic acid → pH 3.8–4.5 → colonization resistance. You the first link: estrogen converts the epithelium from cuboidal to stratified, considerably more resistant to trauma and infection.
• Vulva = mons pubis, labia majora, labia minora, clitoris, vestibule, and the vestibular glands. The vestibule receives the urethral and vaginal openings and the Bartholin ducts.

Note the Bartholin gland as the female homologue of the male Cowper gland, both from the urogenital sinus.

• Bartholin cyst — the commonest vulvar cyst. Mechanism is pure duct obstruction: the greater vestibular gland keeps secreting behind a blocked duct at 4 and 8 o'clock in the vestibule. Sterile and often painless; becomes a painful abscess if it infects. Typically reproductive age, because the gland is estrogen-dependent.
• Skene duct cyst — same mechanism, paraurethral glands, beside the urethral meatus.
• Epidermal inclusion cyst — the commonest vulvar mass overall; keratin trapped by trauma or episiotomy.
• Cyst of the canal of Nuck — a persistent processus vaginalis in the female. Same embryology as the male hydrocele you learned in GU 1.
• How the five insults in the objective damage vulvovaginal tissue: hormonal — loss of estrogen thins the epithelium and raises pH; infectious — candida (thick discharge, pH normal), bacterial vaginosis (pH >4.5, clue cells), trichomonas; inflammatory/dermatologic — lichen sclerosus (thin white atrophic skin, itch, a small squamous carcinoma risk), lichen planus, contact dermatitis; trauma — childbirth, straddle injury; each converges on a breached barrier plus altered pH.

Cervicitis sits between vaginitis and vulvitis — read all three together, since the objective is really about telling them apart.

• Cervicitis is inflammation of the ENDOcervix — the columnar, mucus-secreting epithelium. That single anatomical fact is what separates it from vaginitis, which is disease of the squamous vaginal epithelium.
• Two signs define it: mucopurulent endocervical discharge, and a friable cervix that bleeds on gentle contact with a swab. Both come directly from an inflamed, fragile columnar surface.
• Infectious causes — Chlamydia trachomatis and Neisseria gonorrhoeae are the two to name; also Mycoplasma genitalium, trichomonas and HSV (which gives ulceration rather than mucopus).
• Non-infectious causes — chemical or mechanical irritation, a retained foreign body, and radiation.
• Why it matters more than the symptoms suggest: the endocervix is the gateway to the upper tract. Untreated chlamydial or gonococcal cervicitis ascends to pelvic inflammatory disease, and PID scars the fallopian tubes — the mechanism behind tubal factor infertility and ectopic pregnancy. You the endpoint from the fertility side: salpingitis causes fibrosis in the tubes, thereby occluding them, and he names it a common cause of female sterility.
• Often asymptomatic — which is the entire justification for screening young sexually active women for chlamydia rather than waiting for symptoms.

• Functional cysts are cycle accidents, and you already know the cycle.
  • Follicular cyst — a dominant follicle fails to rupture and keeps accumulating fluid. Thin-walled, unilocular, usually resolves in 4–8 weeks. Recall the mature follicle is 1–1.5 cm at ovulation — so anything much larger and persistent is no longer physiological.
  • Corpus luteum cyst — hemorrhage into the corpus luteum after ovulation. Occurs in the luteal half of the cycle, may rupture and cause acute pain with hemoperitoneum. The corpus luteum reaches 1.5 cm normally.
  • Theca lutein cysts — bilateral, from very high hCG: molar pregnancy, ovulation induction.
• Non-functional but benign: endometrioma ("chocolate cyst) from endometriosis, which as one of the most common causes of female sterility"; and mature cystic teratoma (dermoid) — the commonest ovarian neoplasm in young women, containing tissue from all three germ layers, and the one most likely to torse because it is heavy.
• Malignancy — three families by cell of origin:
  • Epithelial (~90% of ovarian cancer), mostly high-grade serous, and now thought to arise largely from the fallopian tube fimbria rather than the ovarian surface. Older women. BRCA1/2 and Lynch syndrome raise risk.
  • Germ cell — young women and adolescents; dysgerminoma, yolk sac tumor. Marker-producing (LDH, AFP, hCG).
  • Sex cord–stromal — hormone-producing. this one directly: a rare granulosa cell tumor that secretes large quantities of estrogens, causing hypertrophy of the uterine endometrium and irregular bleeding — and he notes that bleeding is often the first and only indication that such a tumor exists, more often after menopause than before. Sertoli–Leydig tumors do the reverse and virilize.
• Why ovarian cancer presents late: the ovary sits free in the peritoneal cavity with no capsule to breach and no lumen to obstruct, so shed cells spread transcoelomically across the peritoneum before any local symptom appears. Bloating, early satiety and urinary frequency are the vague late symptoms. There is no effective screening test — CA-125 is used for monitoring, not detection.

• The pelvic diaphragm is the levator ani + coccygeus. Levator ani has three parts: puborectalis (slings around the anorectal junction and creates the anorectal angle), pubococcygeus, iliococcygeus. The pubococcygeus and puborectalis are the most medial and the most often torn in childbirth.
• The perineal body is the fibromuscular node between vagina and anus — the calls it the final support of the pelvic viscera, linking muscles that extend across the pelvic outlet, like crossing beams supporting the overlying pelvic diaphragm.
• Endopelvic fascia — the paracolpium suspends the vagina; tearing it removes the support that holds the bladder and urethra in place.
• The mechanism of prolapse, verbatim in effect: stretching or tearing of the levator ani and pelvic fascia during childbirth, or disruption of the perineal body by trauma, inadequately repaired episiotomy, inflammation or infection, removes support from the pelvic floor — and prolapse follows.
• The four contributors named in your objective, each mapped: childbirth — direct muscle and fascial tearing; aging — loss of muscle bulk and estrogen-dependent connective tissue; raised intra-abdominal pressure — chronic cough, obesity, constipation, heavy lifting, each a repeated downward load; connective-tissue weakness — collagen disorders and genetic predisposition.
• Naming by compartment: cystocele (bladder into the anterior vaginal wall), urethrocele, rectocele (rectum into the posterior wall), enterocele (small bowel into the pouch), uterine/vault prolapse. Staged by POP-Q, referenced to the hymenal ring.

The mechanism below matches the objective almost word for word.

• The mechanism, verbatim — this is the objective: torsion is "almost always associated with ovarian enlargement, generally due to ovarian cysts or masses. The enlargement causes the ovary to twist, creating a fulcrum around which the oviduct revolves. Initial blockage of venous return causes congestion, leading to decreased distal arterial blood flow, which produces ischemia and necrosis of the ovary."
• Read that order again, because it is the whole answer: venous obstruction → congestion and edema → reduced arterial inflow → ischemia → necrosis. The veins fail first because they are thin-walled and low-pressure; the swelling that follows is what finally defeats the artery.
• Adnexal torsion — ovary AND oviduct together — is more common than torsion of the ovary alone.
• Nearly 70% occur on the RIGHT, for two anatomical reasons: the utero-ovarian ligament is longer on the right, and the sigmoid colon on the left limits space for movement.
• Risk factors: pregnancy (enlarged corpus luteum), large ovarian cysts or tumors, polycystic ovaries, chemical induction of ovulation (ovarian hyperstimulation syndrome), and tubal ligation. It occurs at all ages — infants, adolescents and postmenopausal women included.
• Presentation is less classic than textbooks suggest. Classically sudden, severe, unilateral lower abdominal pain, often after exertion — but half of patients report gradual, intermittent pain, and atypical presentations are common. Nausea and vomiting in 70%.
• The exam is unreliable too: classically unilateral adnexal tenderness with a latero-uterine mass, but nearly 30% have BILATERAL adnexal tenderness and a minority have no tenderness at all.
• The number that should change your behavior: 50% of patients are initially misdiagnosed.
• Imaging: transvaginal ultrasound with Doppler is the primary modality, but it is not 100% sensitive or specific. The commonest finding is an ovary larger than 4 cm from cyst, tumor or edema.
• In children and adolescents the rule flips: torsion is more likely to occur in an otherwise NORMAL ovary, without a cyst or mass — which is part of why pediatric torsion is so often diagnosed late and the ovary lost. Incidence peaks in the first year of life, at menarche, and during pregnancy.

• PCOS is one of the most common endocrine disorders in women, affecting approximately 6%, and it is associated with marked increases in ovarian androgen production and insulin resistance. That covers one of your objective's three components.
• The self-reinforcing loop — this is the answer to the objective:
  • Insulin resistance → compensatory hyperinsulinemia.
  • Insulin acts synergistically with LH on theca cells → more androgen; and insulin suppresses hepatic sex hormone-binding globulin → more free testosterone. Two hits on androgen from one hormone.
  • Androgen excess causes follicular arrest — many small antral follicles, none becoming dominant → anovulation.
  • Anovulation → no corpus luteum → no progesterone → loss of the progesterone brake on GnRH pulse frequency → faster GnRH pulses favor LH over FSH → a raised LH:FSH ratio → still more theca androgen. The loop closes.
• Consequences follow directly from that loop: hyperandrogenism (hirsutism, acne), oligo/amenorrhea, infertility, and — because estrogen is unopposed by progesterone — endometrial hyperplasia and carcinoma risk.
• frames PCOS as a problem of persistent anovulation linked to hyperinsulinemia, and lists its presenting frequencies: menstrual disturbance 66%, infertility 73%, hyperandrogenism 48%, obesity 38%. Rotterdam criteria: 2 of 3 — oligo/anovulation, clinical or biochemical hyperandrogenism, polycystic ovarian morphology on ultrasound. Note that cysts are neither necessary nor sufficient, which is why the name is misleading.

• The bladder is smooth muscle in three interlacing layers, together called the detrusor. Contraction of the detrusor alone can raise bladder pressure to 40–60 mm Hg — the single step that empties the bladder.
• The trigone is the triangle between the two ureteric orifices and the internal urethral orifice; its mucosa is smooth, unlike the rugated rest of the bladder.
• Ureters enter obliquely through the bladder wall, running several centimeters beneath the mucosa. Rising intravesical pressure compresses that intramural tunnel closed — a passive flap-valve that prevents reflux.
• The internal sphincter is detrusor and elastic tissue at the bladder neck — smooth muscle, involuntary. Its natural tone keeps urine out of the posterior urethra.
• The external sphincter is skeletal muscle in the urogenital diaphragm — voluntary, under conscious control, and can hold urine even against strong involuntary contractions.

• It is a spinal reflex, but it is under cerebral veto. Stretch receptors in the bladder wall — especially the posterior urethra — send signals via the pelvic nerves to the sacral cord, which returns parasympathetic outflow to the detrusor.
• It is self-regenerative: contraction stretches the receptors further, which strengthens the contraction. The cycle repeats, each wave larger, until the bladder either empties or the reflex fatigues and the bladder relaxes for minutes to an hour before trying again.
• Two brain centers, opposite jobs:
  • Facilitatory and inhibitory centers in the brain stem (mainly the pons)
  • Inhibitory centers in the cerebral cortex, which keep the reflex partially inhibited except when micturition is desired
• How voluntary voiding actually works, in the sequence: contract the abdominal muscles to raise pressure, which forces extra urine into the bladder neck and posterior urethra, stretching those walls and exciting the stretch receptors — which triggers the reflex — and simultaneously inhibit the external sphincter.

• Compliance is why filling is nearly pressure-free. the cystometrogram: as the first 30–50 mL enters, pressure rises to 5–10 cm H₂O; between 30 and 300 mL the pressure curve is almost flat — the "law of Laplace" plateau of a hollow organ with plastic tone. Fibrosis (radiation, chronic obstruction, chronic infection) destroys compliance, so pressure rises early and steeply.
• Capacity is normally 300–400 mL. The first desire to void appears near 150 mL; a marked sense of fullness near 400 mL.
• Sensation travels with the parasympathetic pelvic nerves. Lose it (diabetic neuropathy, cauda equina) and the bladder overfills silently — a large residual with no urge.
• Outlet resistance must exceed detrusor pressure to store, and fall below it to void. Continence is therefore a pressure competition, not a single structure.

three neurogenic bladders by where the lesion is. Learn them by lesion site, not by name.

• The overflow mechanism, stated plainly: when the bladder is chronically overfilled and stretched, urine dribbles out a few drops at a time — the classic overflow incontinence of a high post-void residual.

Older material does not use the term OAB and treats this under neurogenic bladder instead.

• The wording used: "Hallmark symptom: urgency — a sudden, compelling desire to pass urine that is difficult to defer." Other symptoms: frequency, nocturia, ± urgency urinary incontinence.
• Pathophysiology, as taught: a multifactorial disorder of bladder storage that "may involve detrusor overactivity, altered bladder sensory/afferent signaling, and neurologic dysfunction" — and it is diagnosed clinically rather than by demonstrating a specific underlying mechanism.
• Usually accompanied by frequency (>8 voids/day), nocturia, and with or without urgency incontinence — hence "OAB wet" and "OAB dry."
• Diagnosis, as taught: "initial evaluation = history + physical examination + urinalysis." Do NOT routinely order cystoscopy, imaging or urodynamics — only diagnostic uncertainty or red flags (hematuria, recurrent UTI, neurologic symptoms) prompt them.
• Management ladder, as taught: behavioral first (bladder training, timed voiding, pelvic floor muscle training, fluid management, reduce irritants) → antimuscarinics or β3 agonists → refractory: onabotulinumtoxinA, sacral neuromodulation, or percutaneous tibial nerve stimulation.
• Mechanism — detrusor overactivity: involuntary detrusor contractions during the filling phase, from loss of central inhibition (stroke, MS, Parkinson, dementia), afferent hypersensitivity, or idiopathic urothelial signaling.
• Why the drugs are what they are: detrusor contraction is parasympathetic via muscarinic M3 receptors → antimuscarinics block it. Detrusor relaxation during filling is sympathetic via β3 → β3 agonists (mirabegron) enhance it. The pharmacology falls straight out of the innervation table above.

Your Bladder lecture covers urge, stress and overflow incontinence by name. tabulates the neurogenic causes — upper vs lower motor neuron lesions, and which produce overflow versus urgency. Only overflow; the only stress.

• Effects on health, function and quality of life — the second half of that objective, and the half people forget: falls and fractures (rushing to the toilet at night), skin breakdown and UTI, sleep loss, social withdrawal and depression, caregiver burden, and it is a leading contributor to nursing-home placement.

• 0. The follicle is the unit. Closed follicles 100–300 μm across, lined by cuboidal cells, filled with colloid whose main constituent is thyroglobulin. Blood flow is about five times the weight of the gland per minute — among the highest in the body.
• 1. Iodide trapping. The sodium-iodide symporter (NIS) on the basolateral membrane co-transports 1 iodide with 2 sodium, powered indirectly by Na⁺-K⁺ ATPase. It concentrates iodide ~30× plasma, up to 250× when maximally active. TSH stimulates it.
• 2. Efflux into the follicle across the apical membrane by pendrin, a chloride-iodide counter-transporter.
• 3. Thyroglobulin secretion. A glycoprotein of MW ~335,000 containing about 70 tyrosine residues, secreted into the colloid.
• 4. Oxidation of iodide to nascent iodine by thyroid peroxidase plus hydrogen peroxide, at the apical membrane. Block or genetically lose peroxidase and the rate of formation of thyroid hormones falls to zero.
• 5. Organification — iodine binds tyrosine residues within thyroglobulin, forming MIT then DIT, in seconds to minutes.
• 6. Coupling. DIT + DIT → T4. MIT + DIT → T3 (about one-fifteenth of the product). DIT + MIT the other way → reverse T3, which has no known function in humans.
• 7. Storage, then release. The thyroid is unique among endocrine glands in storing large amounts of hormone — up to 30 T4 molecules per thyroglobulin, enough for 2–3 months of normal requirement. Release requires pinocytosis of colloid back into the cell, then proteases free T4 and T3.

• Output is 93% T4 and 7% T3, but almost all T4 is converted to T3 in the tissues, and T3 is about four times as potent — present in smaller amounts and for a much shorter time.
• T4 is the reservoir; T3 is the active hormone. Peripheral 5'-deiodinase makes T3; the alternative deiodination makes inactive reverse T3, and illness or starvation shifts conversion toward rT3.
• Bound in plasma mainly to thyroxine-binding globulin. This is why total T4 rises in pregnancy and on estrogen while free T4 and the patient stay normal — the Endo 1 free-vs-total rule.
• The axis: hypothalamic TRH → pituitary TSH → follicular cell cAMP → every step above, from iodide trapping to proteolysis, plus growth of the gland itself. Feedback is primarily free thyroid hormone onto the anterior pituitary, with evidence of hypothalamic feedback too, and the summary is that it maintains an almost constant concentration of free thyroid hormones.

Also in hyperthyroidism, thyrotoxicosis, Graves disease; hypothyroidism ; thyroid structure and function.

• Graves' disease is the commonest form and is autoimmune. Thyroid-stimulating immunoglobulins (TSIs) bind the TSH receptor and cause continual cAMP activation. The key detail: TSIs stimulate for as long as 12 hours, versus a little over 1 hour for TSH — a receptor agonist that never lets go.
• Therefore TSH is LOW — often essentially zero — in almost all Graves' patients, because the hormone excess suppresses the pituitary. A high T4 with a high TSH is a different disease entirely (TSH-secreting adenoma or resistance).
• The gland grows 2–3× with hyperplasia and follicular infolding, and can secrete at 5–15 times the normal rate.
• Toxic adenoma is the contrast case: a single autonomous nodule, not autoimmune, and it suppresses the rest of the gland because its hormone output shuts off TSH — so the scan shows one hot nodule and a cold remainder.
• Symptoms, all predictable from a raised metabolic rate: excitability, heat intolerance, sweating, weight loss despite appetite, diarrhea, muscle weakness, nervousness, fatigue with inability to sleep, hand tremor. BMR runs +30 to +60.
• Exophthalmos is a separate autoimmune process, not a metabolic one. Edematous swelling of retro-orbital tissue and degeneration of extraocular muscle; immunoglobulins reacting with eye muscle are found, highest in patients with high TSI. Occurs to a major degree in about a third of patients.
• Diagnosis: the most accurate test is free T4. TSH is suppressed. TSI is high in Graves' but low in adenoma — the test that separates them.

• Hashimoto's thyroiditis is the mirror image of Graves': autoimmunity that destroys rather than stimulates. Thyroiditis → progressive deterioration → fibrosis → diminished or absent secretion.
• Endemic colloid goiter from iodine deficiency — the mechanism is worth tracing because it explains a big gland with low hormone: no iodine → no hormone → no negative feedback → TSH rises → the gland is driven to grow and secretes enormous quantities of thyroglobulin colloid into the follicles. A huge goiter that is still hypothyroid.
• Effects are the inverse of hyperthyroidism, with BMR falling 40–50% below normal in complete absence of secretion. Fatigue, somnolence (sleep of 12–14 hours a day), cold intolerance, weight gain, constipation, slowed mentation, muscle sluggishness, bradycardia, decreased cardiac output.
• Myxedema — the characteristic bagginess under the eyes and puffy face is not ordinary edema: greatly increased quantities of hyaluronic acid and chondroitin sulfate bound with protein form excess interstitial gel, which is why it does not pit.
• Atherosclerosis: hypothyroidism raises blood cholesterol because of altered fat metabolism — so long-standing hypothyroidism accelerates arterial disease.
• Cretinism — extreme hypothyroidism in fetal life or infancy. The point about it is the skeletal one: bone growth is inhibited more than soft tissue growth, so the child is disproportionately short and obese-appearing, and neurological damage is permanent unless treated within weeks of birth.
• Treatment: a single daily oral dose of thyroxine is enough because of its long half-life.

• Two inputs, as in the male: psychic and local. Desire rises with sex hormone levels and peaks near ovulation, probably from the high preovulatory estrogen.
• Afferent path: stimulation of vulva, vagina and perineum — the glans of the clitoris is especially sensitive — travels via the pudendal nerve and sacral plexus to the sacral cord, then to the cerebrum. Local reflexes are integrated in the sacral and lumbar cord.
• Erection and lubrication are PARASYMPATHETIC. Erectile tissue around the introitus and in the clitoris is almost identical to the erectile tissue of the penis, controlled by parasympathetics through the nervi erigentes. Arterial dilation is mediated by acetylcholine, nitric oxide and vasoactive intestinal polypeptide.
• Lubrication has three sources: the Bartholin glands beneath the labia minora (parasympathetically driven), vaginal epithelial mucus, and a small contribution from male urethral glands.
• Orgasm is analogous to male emission and ejaculation: rhythmic perineal muscle contraction from spinal reflexes, possible oxytocin release increasing uterine contractions, and cervical canal dilation for up to 30 minutes — all plausibly aiding sperm transport, since women are known to be somewhat more fertile after intercourse than after artificial insemination. Then resolution.

• 15–20 lobes radiating from the nipple, each drained by a lactiferous duct. Each lobe is made of lobules containing the alveoli (acini) that actually secrete milk.
• The terminal duct lobular unit is the functional unit — and clinically the origin of most breast lesions. "cysts develop more commonly in terminal ducts and lobules."
• Two cell layers line the ducts and alveoli: an inner secretory epithelium and an outer myoepithelial layer that contracts under oxytocin — "a layer of epithelial cells capable of secreting milk and a layer of subepithelial cells capable of contracting. exactly this action — oxytocin causes myoepithelial cells" surrounding the alveoli to contract, expressing milk into the ducts.
• Suspensory (Cooper's) ligaments run from dermis to deep fascia. The mechanism of each carcinoma sign: nipple retraction from shortening of the mammary ducts, skin pitting from obstruction of the subcutaneous lymphatics, arm edema from axillary lymphatic obstruction, local pain from tumor involvement of the pectoralis fascia.
• Lymphatic drainage drives staging: most goes to the axillary nodes — which is why axillary obstruction produces arm edema.
• Stroma matters: estrogen deposits large quantities of fat in the stroma — breast mass is substantially fat, which is why size does not predict milk capacity.

• Four more hormones are required for ductal growth and are easy to forget: growth hormone, prolactin, adrenal glucocorticoids and insulin — all protein-metabolism hormones.

• Puberty: thelarche is estrogen-driven ductal growth plus fat deposition — the first sign of puberty in girls.
• Menstrual cycle: luteal-phase progesterone causes lobuloalveolar proliferation and fluid retention → cyclical premenstrual swelling and tenderness, resolving with menstruation. The swelling partly to secretory development and partly to increased tissue fluid.
• Pregnancy: "far greater growth occurs during the high-estrogen state of pregnancy, and only then does the glandular tissue become completely developed for production of milk."
• Lactation: the numbers — about 1.5 L/day at peak, with a metabolic drain of roughly 50 g fat, 100 g lactose and 2–3 g calcium phosphate daily; without dietary calcium the mother's parathyroid glands enlarge and bone decalcifies. Also, lactation suppresses gonadotropins, which is why ovulation is often absent for the first months.
• Menopause: fibrous tissue increases progressively until menopause and regresses thereafter — glandular involution and fatty replacement, which is why mammographic density falls with age and mammography becomes more sensitive.

• Estrogen initiates growth of the breast and its milk-producing apparatus and is responsible for the mature external form — but is careful: it does not complete the job of converting the breasts into milk-producing organs.
• Progesterone completes lobule and alveolar development and causes the cells to become secretory.
• SERMs at the breast are ANTAGONISTS — both tamoxifen and raloxifene. That is the whole basis of tamoxifen in ER-positive breast cancer and of risk reduction in high-risk women.
• The tissue-selectivity table you need is short: tamoxifen — breast antagonist, endometrium agonist, bone agonist. Raloxifene — breast antagonist, endometrium antagonist, bone agonist. Aromatase inhibitors are different again: they cut estrogen synthesis rather than block the receptor, and work only after menopause, when peripheral aromatization is the main source.

The territory: galactorrhea, benign and fibrocystic change, fibroadenoma, nipple discharge, fat necrosis, breast abscess, mastalgia, the palpable breast mass, gynecomastia, and carcinoma of the female and male breast.

• Galactorrhea = milky discharge, usually bilateral and from multiple ducts, occurring outside pregnancy and lactation. Distinguish it from physiologic lactation (appropriate to context) and from pathologic nipple discharge — which is unilateral, from a single duct, and bloody or serous, and points at papilloma or carcinoma rather than at prolactin.
• The mechanism is loss of dopamine inhibition. you the workup as an algorithm — galactorrhea and amenorrhea are worked up together, starting with urine hCG, then serum prolactin, then TSH, with hyperprolactinemia defined at >100 ng/mL and a lateral sella turcica film if prolactin is high. Prolactin is the one anterior pituitary hormone under tonic inhibition — dopamine from the hypothalamus. Anything that cuts the dopamine signal raises prolactin: dopamine antagonists (antipsychotics, metoclopramide), stalk compression by any sellar mass, prolactinoma, primary hypothyroidism (high TRH stimulates prolactin), pregnancy, chest wall stimulation, renal failure.
• Gynecomastia = true glandular proliferation of male breast tissue — a firm, concentric, rubbery disc beneath the areola, often tender. Pseudogynecomastia is fat alone: soft, diffuse, no discrete subareolar disc.
• You the principle behind it: the primordial breasts of females and males are exactly alike, and under appropriate hormones the male breast can develop sufficiently to produce milk in the same manner as the female breast. Male breast tissue is not absent — it is unstimulated.
• So gynecomastia is a RATIO problem, not an absolute one. A rise in estrogen relative to androgen at the breast drives proliferation. The example: a testicular tumor containing placental tissue secretes estrogens and causes the condition called gynecomastia.
• Working the ratio explains every cause: more estrogen — cirrhosis (reduced clearance plus increased aromatization), obesity (adipose aromatase), hCG-secreting or Leydig/Sertoli tumors, exogenous estrogen. Less androgen — hypogonadism, Klinefelter, aging, spironolactone and ketoconazole (synthesis and receptor blockade), anabolic steroid use (suppresses LH, and excess substrate is aromatized). Physiologic peaks: newborn (maternal estrogen), puberty (transient estrogen-first surge), elderly (falling testosterone plus rising adipose aromatase).

• About 3 cm long, 4 cm wide, 2 cm deep — the calls it "firm, walnut-size," the largest accessory gland of the male reproductive system, and it surrounds the prostatic urethra.
• It has a fibrous capsule enclosed in a dense prostatic sheath continuous with the puboprostatic ligaments, and it is embedded in the prostatic venous plexus.
• The three zones are the examinable part:
  • Transition zone — surrounds the urethra proximally. ~5% of volume, but the site of BPH.
  • Central zone — surrounds the ejaculatory ducts. Rarely diseased.
  • Peripheral zone — the largest, posterior and lateral. ~70% of volume, and the site of ~70–80% of carcinoma — and it is the part palpable on rectal examination.
• Histologically it is a tubuloalveolar gland in a fibromuscular stroma — the stroma matters, because BPH is stromal and epithelial, and because the smooth muscle in it is what α-blockers relax.
• Growth is androgen-dependent: the gland is essentially quiescent until puberty, then under testosterone enlarges markedly, reaching an almost stationary size by age 20 and holding it to about 50.

• Superiorly: the base of the prostate is continuous with the bladder neck — there is no clean plane between them, which is why prostatic enlargement raises the bladder floor.
• Through it: the prostatic urethra runs from base to apex, closer to the anterior surface. Its posterior wall bears the urethral crest with the seminal colliculus, flanked by the prostatic sinuses into which the prostatic ductules open.
• The ejaculatory ducts — formed by union of the ductus deferens with the duct of the seminal gland — enter the posterosuperior prostate and open onto the seminal colliculus, beside the prostatic utricle. So the reproductive and urinary tracts converge inside the prostate.
• Inferiorly: the apex sits on the external urethral sphincter and the urogenital diaphragm — the anatomical reason prostate surgery risks stress incontinence.
• Posteriorly: the rectum, separated only by the rectovesical septum — which is why the peripheral zone is palpable per rectum, and why advanced disease can invade the rectum.
• Anteriorly: the retropubic space and the prostatic venous plexus, which drains to the internal vertebral venous plexus — the classic route for vertebral metastasis.

• Prostatic fluid is thin and MILKY, containing calcium, citrate ion, phosphate ion, a clotting enzyme and a profibrinolysin.
• It is ALKALINE, and that is its job. Vaginal secretions are acidic (pH 3.5–4.0) and sperm are not optimally motile until pH rises to about 6.0–6.5. The alkaline prostatic fluid neutralizes the acidity of the other seminal fluids and of the vagina, and thereby enhances the motility and fertility of the sperm.
• The clot-then-liquefy sequence: the prostatic clotting enzyme acts on fibrinogen from the seminal vesicles to form a weak coagulum that holds semen in the deep vagina; within 15–30 minutes the profibrinolysin becomes fibrinolysin and lyses the clot, releasing highly motile sperm.
• Contributions to semen: vas deferens ~10%, seminal vesicles ~60% (fructose, citric acid, prostaglandins, fibrinogen), prostate ~30%, bulbourethral glands a small amount. Average pH ~7.5.
• Seminal vesicle fructose is the sperm's fuel, and its prostaglandins may aid fertilization by making cervical mucus more receptive and by causing reverse peristalsis in the uterus and tubes.

• Testosterone is the circulating hormone; DHT is the prostatic one. much of the testosterone entering target cells is converted by 5α-reductase to dihydrotestosterone, and it is DHT that binds the cytoplasmic receptor — this conversion occurs especially in the prostate gland.
• DHT binds the androgen receptor with higher affinity than testosterone and dissociates more slowly, so the same circulating testosterone produces a much stronger prostatic signal.
• Developmentally, DHT drives formation of the prostate, penis and scrotum — which is why 5α-reductase deficiency gives normal Wolffian ducts but a hypoplastic prostate.
• Lifelong dependence: after about 50, in some men the prostate involutes along with decreased testicular testosterone production. Remove androgen and the gland shrinks — the basis of androgen-deprivation therapy.
• Control comes from above: hypothalamic GnRH → pituitary LH → Leydig cells → testosterone, with testosterone feeding back negatively on both. FSH acts on Sertoli cells for spermatogenesis, not on the prostate.

• What the standard texts actually say is thin. "a benign prostatic fibroadenoma frequently develops in the prostate in many older men and can cause urinary obstruction. This hypertrophy is caused not by testosterone but instead by abnormal overgrowth of prostate tissue." That framing does not develop the mechanism the objective asks for.
• The definition, worth memorizing as written: BPH is a "nonmalignant proliferation of stromal and epithelial tissue in the prostatic transition zone," which "may cause prostate enlargement and bladder outlet obstruction." It then makes a distinction most students miss: BPH, prostate enlargement, obstruction, and LUTS are related but are not exactly the same thing.
• The pathophysiology chain, verbatim: "Androgen exposure, particularly dihydrotestosterone (DHT), promotes stromal and glandular growth… DHT → prostate growth → bladder outlet obstruction → increased urinary resistance, detrusor muscle hypertrophy, and decreased bladder compliance." That single line answers both this objective and the outlet-obstruction one below.
• Risk factors: age, Black race, obesity, diabetes, hypertension, sedentary lifestyle, high alcohol intake, and familial clustering.
• The three drivers named in your objective:
  • Aging — prevalence rises steeply from the 40s; histologic BPH is near-universal by 80.
  • DHT — the permissive factor. It is required, but the level is not raised; the gland's sensitivity and local 5α-reductase type 2 activity are what change. Men with congenital 5α-reductase deficiency never develop BPH — the cleanest proof that DHT is necessary.
  • Stromal and epithelial hyperplasia — a true increase in cell number (hyperplasia, not hypertrophy, despite the old name), with stroma proliferating out of proportion to epithelium, giving the characteristic firm nodules.
• Note the discrepancy and hold both: the enlargement is caused not by testosterone. That is true in the sense that testosterone levels do not rise — but DHT is nonetheless required. If a stem asks, the modern answer is DHT-dependent, not androgen-excess.

• The material does not use those words, though it describes both halves. Static component = the physical bulk of transition-zone tissue compressing the prostatic urethra. It is why prostate size correlates with obstruction — and it is what 5α-reductase inhibitors reduce, slowly.
• Dynamic component = α₁-adrenergic smooth muscle tone in the prostatic stroma and bladder neck. It is why symptoms fluctuate with stress and decongestants, why a small gland can obstruct badly, and why α-blockers work within days while finasteride takes months.
• The symptoms separate into three groups — storage (frequency, urgency, nocturia), voiding (hesitancy, weak stream, intermittency, straining) and post-void (incomplete emptying, dribbling) — and flags dysuria, fever, gross hematuria, pelvic/perineal pain or neurologic symptoms as reasons to consider another diagnosis.
• Downstream consequences run through the GU 2 physiology you already know: obstruction → detrusor must generate higher pressure → detrusor hypertrophy and trabeculation → reduced compliance and detrusor overactivity (so BPH produces storage symptoms, not only voiding ones) → eventually decompensation with high residual and overflow incontinence → back-pressure → hydronephrosis and postrenal injury.
• The names the anatomical direction of trouble: the enlarging transition zone projects into the bladder and impedes urination by distorting the prostatic urethra.

Three topics sit together here: BPH, PSA and prostate cancer, and prostatitis.

• Acute bacterial prostatitis — usually ascending uropathogens (E. Coli). Fever, perineal and low back pain, obstructive symptoms, and an exquisitely tender, boggy prostate. Do not perform vigorous prostatic massage — it can seed bacteremia.
• Chronic bacterial prostatitis — the classic cause of recurrent UTI in a man, because the gland is a reservoir the antibiotic penetrates poorly.
• Chronic pelvic pain syndrome is by far the commonest form and is non-bacterial — pain without infection.
• Prostate cancer — cancer of the prostate gland is a different problem from BPH, and accounts for 2–3% of all male deaths; it is androgen-dependent, so it can be inhibited by removing the testes or by estrogen administration, and about 10% of men develop it.
• The adds the exam findings: the malignant gland is hard and often irregular or nodular on DRE, in contrast to the smooth, symmetric, rubbery enlargement of BPH.
• Metastasis is characteristically to bone, and characteristically osteoblastic (sclerotic) — unusual among carcinomas, which are typically lytic. The route is the prostatic venous plexus to the internal vertebral venous plexus, hence the lumbar spine and pelvis.

• Fed state = insulin. Glucose is taken up and stored — glycogen in liver and muscle, triglyceride in adipose, protein synthesis everywhere. Insulin is, in the phrase, a hormone associated with energy abundance.
• Fasting state = glucagon, then the counter-regulatory hormones. Glycogenolysis, then gluconeogenesis, then lipolysis and ketogenesis.
• The single most important design constraint: glucose is the only nutrient the brain, retina and gonadal germinal epithelium can normally use in sufficient quantity. Everything about glucose regulation exists to protect the brain.
• The four defenses, in the order they engage:
  • 1. The liver buffers — it takes up glucose after a meal and returns it between meals, so swings are damped before any hormone acts.
  • 2. Insulin and glucagon — the two-way feedback. Insulin dominates normally; glucagon becomes valuable in starvation and exercise.
  • 3. Sympathetic outflow — severe hypoglycemia acts directly on the hypothalamus → epinephrine → hepatic glucose release.
  • 4. Growth hormone and cortisol — over hours and days, they reduce glucose utilization and shift the body to fat.
• A subtlety makes explicit: during the interdigestive period it is important that the pancreas NOT secrete insulin — otherwise the scant glucose would go into muscle leaving the brain without a nutritive source.

• Synthesis: preproinsulin → proinsulin → cleaved to insulin plus C peptide, both secreted. About one-sixth of secreted product remains unconverted proinsulin, which has almost no insulin activity.
• Very short half-life: insulin circulates almost entirely unbound with a plasma half-life of about 6 minutes and is cleared in 10–15 minutes, mostly by the liver.
• The secretion mechanism — worth knowing step by step: glucose enters the β cell via GLUT2 → phosphorylated by glucokinase, the rate-limiting glucose sensor → oxidized to ATP → ATP closes K⁺ channels → membrane depolarizes → voltage-gated Ca²⁺ channels open → calcium influx triggers exocytosis.
• The receptor: a tetramer of two α subunits (outside, bind insulin) and two β subunits (span the membrane). Binding causes autophosphorylation of the β subunits, activating a tyrosine kinase → phosphorylation of insulin-receptor substrates (IRS).
• Effects are staged in time: within seconds, glucose uptake rises in muscle and adipose by GLUT4 translocation; within minutes, enzyme phosphorylation states change; over hours to days, gene transcription changes.
• The brain, liver and exercising muscle are the exceptions — brain uptake is insulin-independent (GLUT1/GLUT3), and exercising muscle takes up glucose without insulin. This is why hypoglycemia hits the brain first and why exercise lowers glucose in type 1 diabetes.

• Secreted by alpha cells when glucose falls; the "hyperglycemic hormone." Its two major effects on the liver are glycogenolysis and increased gluconeogenesis.
• It is extraordinarily potent: as little as 1 µg/kg raises blood glucose about 20 mg/dL in 20 minutes.
• Mechanism: glucagon → cAMP → protein kinase A → phosphorylase activation → glycogen split to glucose-1-phosphate → dephosphorylated and released. Note it acts on liver, not muscle, because muscle lacks glucose-6-phosphatase and cannot export glucose.
• Regulation: hypoglycemia is the main stimulus; high amino acids also stimulate it — which prevents a protein meal from causing hypoglycemia, since amino acids also stimulate insulin.

Also in : diabetes mellitus, type 1, type 2; hypoglycemia, diabetic ketoacidosis, hyperosmolar hyperglycemic nonketotic syndrome, Somogyi effect .

the definition: diabetes mellitus is "a syndrome of impaired carbohydrate, fat, and protein metabolism caused by either lack of insulin secretion or decreased sensitivity of the tissues to insulin." Note it is not a glucose disease — it is a fuel-metabolism disease.

• Type 1's three sequelae, in the order: (1) increased blood glucose, (2) increased use of fats for energy and cholesterol formation by the liver, (3) depletion of the body's proteins.
• Why an untreated type 1 patient loses weight while eating constantly: failure to use glucose for energy → increased utilization and decreased storage of protein and fat → rapid weight loss and asthenia despite polyphagia.
• Where type 2's resistance actually lies: obese subjects have somewhat fewer insulin receptors, but most of the resistance is post-receptor — "abnormalities of the signaling pathways that link receptor activation with multiple cellular effects," likely related to toxic lipid accumulation in skeletal muscle and liver.

• HbA1c — glucose binds hemoglobin irreversibly, and once hemoglobin is glycated, it remains that way for the life of the cell. Since red cells live about 120 days, HbA1c reflects the average glucose over roughly the previous three months.
• Glucose tolerance test — after 1 g/kg oral glucose, a normal person rises from ~90 to 120–140 mg/dL and returns below baseline within about 2 hours. In diabetes the rise is much greater, the fall takes 4–6 hours, and it fails to fall below the control level.
• The type-discriminating step: measure plasma insulin — low or undetectable in type 1, increased in type 2.
• Fasting glucose in diabetes is almost always above 115 mg/100 ml and often above 140.
• Acetone breath — acetoacetic acid is converted to volatile acetone, so type 1 diabetes can sometimes be diagnosed simply by smelling acetone on the breath.

• Current diagnostic thresholds — use these: HbA1c ≥6.5%; fasting plasma glucose ≥126 mg/dL; 2-hour OGTT ≥200 mg/dL; or random ≥200 with classic symptoms. Prediabetes: A1c 5.7–6.4%, fasting 100–125.
• the underlying principle: in the normal 120-day red cell lifespan glucose joins hemoglobin, and "once a hemoglobin molecule is glycosylated, it remains that way." When HbA1c misleads: anything that shortens red cell life falsely lowers it (hemolysis, recent transfusion, blood loss); iron deficiency and reduced turnover falsely raise it. The logic follows directly from the "life of the cell" statement.

• The chain, in the terms: shift from carbohydrate to fat metabolism → release of keto acids (acetoacetic and β-hydroxybutyric) into plasma faster than tissues can oxidize them → metabolic acidosis → with dehydration, severe acidosis... Leads rapidly to diabetic coma and death unless the patient is treated immediately with large amounts of insulin.
• The compensations are the ones from acid–base: rapid deep breathing (Kussmaul) blows off CO₂ but depletes bicarbonate stores; the kidneys decrease bicarbonate excretion and generate new bicarbonate.
• The numbers for diabetic coma — worth memorizing as a picture: glucose 180 → >400 mg/dL; keto acids 1 → 30 mEq; bicarbonate 27 → 5 mEq; pH 7.4 → 6.9. Below pH ~7.0, acidotic coma and death can occur within hours.
• Why DKA is a type 1 disease and HHS a type 2 one — one mechanism. Suppressing lipolysis takes much less insulin than promoting glucose uptake. A type 2 patient retains just enough insulin to restrain hormone-sensitive lipase, so no ketones form — but not enough to control glucose, which climbs far higher and drives an osmotic diuresis to profound dehydration. Hence HHS: glucose often >600, osmolality >320, minimal ketosis, worse dehydration and worse mortality. Type 1 has no insulin, so lipolysis is unrestrained and ketosis dominates at a lower glucose.
• The potassium trap. In DKA, acidosis and insulin deficiency drive potassium out of cells, so serum potassium reads normal or high while total body potassium is severely depleted. Insulin drives it back — so potassium falls fast during treatment, and must be replaced before or alongside insulin.

• The five features of the metabolic syndrome: (1) obesity, especially abdominal fat; (2) insulin resistance; (3) fasting hyperglycemia; (4) lipid abnormalities — raised triglycerides, low HDL; (5) hypertension. He adds that all of them are closely related to accumulation of excess adipose tissue in the abdominal cavity around the visceral organs.
• The formal criteria (any 3 of 5): waist >102 cm men / >88 cm women; triglycerides ≥150; HDL <40 men / <50 women; BP ≥130/85; fasting glucose ≥100.
• Why VISCERAL fat and not just fat — three mechanisms: it drains via the portal vein, delivering free fatty acids straight to the liver; it is more lipolytically active; and it is more inflammatory, infiltrated by macrophages.
• Adipokines — adipose is an endocrine organ, not a storage depot: leptin (rises with fat mass; obesity is a state of leptin resistance), adiponectin (insulin-sensitizing and anti-inflammatory, and uniquely it falls as fat mass rises), TNF-α and IL-6 (impair insulin signaling — the molecular link between inflammation and resistance), resistin, and PAI-1 (prothrombotic).
• The other causes of insulin resistance in the table, and they are all worth knowing because each is a stem: excess glucocorticoids (Cushing or steroid therapy), excess growth hormone (acromegaly), pregnancy and gestational diabetes, PCOS, lipodystrophy, insulin receptor antibodies or mutations.

• Where: fertilization "normally takes place in the ampulla of one of the fallopian tubes."
• Sperm transport is not just swimming. transport is aided by contractions of the uterus and tubes stimulated by prostaglandins in the male seminal fluid and by oxytocin released from the woman's posterior pituitary during orgasm. Of nearly half a billion sperm deposited, only a few thousand reach each ampulla.
• Two barriers, in order: the sperm must first penetrate the corona radiata (the granulosa cells still attached to the ovum), then bind and penetrate the zona pellucida.
• The timing you should be able to recite: the fertilized ovum enters the uterine cavity 3–4 days after ovulation and implants 7–9 days after ovulation. In between, uterine secretions — them "uterine milk" — nourish the dividing ovum.
• Implantation is invasive from the start: trophoblastic cells on the surface of the blastocyst digest the endometrium and absorb its stored nutrients, which is what makes the secretory endometrium's glycogen and lipid load matter.
• Why implantation timing constrains everything downstream: the corpus luteum has a fixed ~12-day life, so the blastocyst must implant and produce hCG before it involutes. Implant late and the luteal rescue fails — one mechanism of early pregnancy loss.

• The framing of "the pill": appropriate estrogen or progestin given in the first half of the cycle suppresses the preovulatory LH surge, and without that surge ovulation does not occur. He notes the failure rate of hormonal suppression is about 8–9% per year in practice.
• Combined hormonal contraceptives (estrogen + progestin) — the objective names these first. Primary mechanism: suppression of ovulation by negative feedback on FSH and LH, abolishing the mid-cycle surge. Secondary: thickened cervical mucus, thinned endometrium.
• Progestin-only methods — the mechanism shifts. Ovulation suppression is inconsistent, so the dominant effects are thickened cervical mucus (hostile to sperm penetration — the reverse of the thin, sperm-guiding estrogen mucus you learned in WH 1) and endometrial atrophy.
• Levonorgestrel-releasing intrauterine system — the third item your objective names. It acts locally: profound endometrial suppression and thick cervical mucus, with little systemic suppression of ovulation. That local action is why it also treats heavy menstrual bleeding — and why as a route to deliver progestin directly to the uterus in menopausal hormone therapy.

• HCG is the rescue signal. It has almost exactly the same properties as LH, is secreted by the placenta, and prolongs the corpus luteum for the first 2–4 months of pregnancy — preventing the involution that would otherwise trigger menstruation.
• Then the placenta takes over. Placental estrogens and progesterone rise steadily, and after about the fourth month progesterone is largely placental rather than luteal.
• Human chorionic somatomammotropin (hCS/hPL) — a growth-hormone-like placental hormone that shifts maternal metabolism toward fat utilization, sparing glucose for the fetus. This is the mechanism behind the insulin resistance of pregnancy — and the table lists pregnancy and gestational diabetes among the causes of insulin resistance.
• Structural changes that support the pregnancy: the uterus grows from about 50 g to 1100 g, the breasts approximately double, and the vagina enlarges with a wider introitus.

• Average weight gain: 25–35 pounds.
• Amniotic fluid is normally 500 mL to 1 liter; its water turns over every 3 hours, electrolytes about every 15. Much of it is fetal urine, absorbed via fetal gut and lungs.

• Uterine excitability rises toward term from two directions — hormonal and mechanical.
• Hormonal: the estrogen-to-progesterone ratio rises. Progesterone inhibits uterine contractility (the same effect that protected implantation); estrogen increases it. Oxytocin receptors on the myometrium increase greatly toward term, so the same oxytocin concentration produces a far larger response.
• Mechanical: stretch of the uterine musculature increases contractility, and stretch or irritation of the cervix is a particularly potent stimulus.
• Labor is a positive feedback loop — this is the part to be able to draw: cervical stretch → reflex oxytocin release from the posterior pituitary and stronger uterine contraction → the fetal head is pushed harder against the cervix → more stretch → more oxytocin. The cycle escalates until delivery breaks it.
• Abdominal muscle contraction adds a second force once labor is established — a spinal reflex plus voluntary bearing down.

• Contractions begin at the fundus and spread downward, strongest at the top and weak in the lower segment — so each contraction forces the fetus toward the cervix.
• They must be intermittent. Strong contractions impede or sometimes even stop blood flow through the placenta and would cause death of the fetus if the contractions were continuous. the consequence directly: overuse of oxytocin can cause uterine spasm rather than rhythmic contractions and fetal death.
• Frequency escalates from about once every 30 minutes early to once every 1–3 minutes at delivery.
• First stage = progressive cervical dilation until the opening equals the fetal head. 8–24 hours in a first pregnancy, often only minutes after many pregnancies.
• Second stage = passage through the birth canal, from full dilation to delivery. 1 minute to 30+ minutes depending on parity. The membranes usually rupture as the cervix completes dilation.
• Third stage = delivery of the placenta, over the following 10–45 minutes.
• Presentation: the head is first in more than 95% of births; buttocks or feet first is a breech presentation.
• Labor pain has two sources with two nerve supplies — worth knowing because it explains why regional anesthesia is staged. First stage: cramping from hypoxia of uterine muscle as contraction compresses its vessels, carried by visceral sensory hypogastric nerves. Second stage: far more severe pain from cervical, perineal and vaginal stretching, carried by somatic nerves.

• The placenta separates by shearing. For 10–45 minutes the uterus keeps contracting to a smaller size, which shears the placenta off its implantation site — and opens the placental sinuses, causing bleeding.
• Average blood loss is about 350 mL, and the mechanism that limits it is anatomical: the myometrial smooth muscle fibers are arranged in figures of eight around the blood vessels, so uterine contraction after delivery constricts the very vessels that supplied the placenta. Vasoconstrictor prostaglandins at the separation site add further spasm.
• Involution: the uterus falls to less than half its immediate postpartum weight within one week, and can reach pre-pregnancy size by 4 weeks if the mother lactates — because lactation suppresses gonadotropins and ovarian hormones.
• Lochia: the placental site autolyzes, producing a discharge that is first bloody then serous, lasting about 10 days, after which the endometrium re-epithelializes.
• Recall the reserve: the mother carries 1–2 liters of extra blood at term, and normally loses only about a quarter of it at delivery — which is why a healthy woman tolerates blood loss that would be dangerous outside pregnancy.

• Three erectile bodies: paired corpora cavernosa dorsally and a single corpus spongiosum ventrally, which surrounds the spongy urethra and expands distally as the glans. The spongiosum stays comparatively soft during erection — which is what keeps the urethra patent.
• Four urethral segments in the male: preprostatic → prostatic → intermediate (membranous) → spongy. The intermediate part is the shortest, narrowest and least distensible — and it passes through the external urethral sphincter.
• Two anatomical facts that generate disease: the male urethra is long and has two curves and three narrowings, which is why catheterization is harder than in the female and why strictures and instrumentation injuries occur where they do.

• Erection is PARASYMPATHETIC, from the sacral cord via the nervi erigentes. The parasympathetic signals dilate the penile arteries while compressing the veins, so the erectile bodies fill under near-arterial pressure.
• The transmitter chain: parasympathetic fibers release nitric oxide, which raises cyclic GMP, relaxing the trabecular smooth muscle of the cavernous sinusoids. Phosphodiesterase type 5 degrades cGMP — which is precisely why PDE5 inhibitors work, and why they need the parasympathetic signal to be intact to work at all.
• Emission is SYMPATHETIC (L1–L2): peristalsis of the vas deferens and contraction of the seminal vesicles and prostate deliver semen into the internal urethra. Ejaculation then adds rhythmic contraction of the pudendal-innervated bulbospongiosus and ischiocavernosus.
• Bladder-neck closure during emission is sympathetic too — which is why α-blockers and prostate surgery cause retrograde ejaculation. Retrograde ejaculation is a recognized complication of TURP.

• The causes: neurologic, vascular, endocrine, and psychological — and he notes it rises sharply with age. Under sexual dysfunction and impotence, .
• Your objective names four mechanisms — map each to a cause:
  • Impaired arterial inflow — atherosclerosis, diabetes, hypertension. The commonest organic cause, and the reason ED is a marker of systemic vascular disease: the penile arteries are small and declare disease before the coronaries do.
  • Excessive venous outflow — venous leak; the sinusoids fill but cannot hold pressure.
  • Nerve dysfunction — diabetic autonomic neuropathy, pelvic surgery, spinal cord injury.
  • Tissue fibrosis — replacement of compliant cavernous tissue; Peyronie disease is the named example.
• Endocrine and drug causes sit alongside those four: hypogonadism, hyperprolactinemia, thyroid disease; antihypertensives, antidepressants, antiandrogens including the 5α-reductase inhibitors you met in GU 3.

• Urethritis — inflammation of the urethra, most often from sexually transmitted organisms. In men the cardinal features are dysuria and urethral discharge. Note the parallel with cervicitis in WH 2: both are inflammation of the tract's gateway, both frequently gonococcal or chlamydial, and both ascend — to epididymitis in men, to PID in women.
• Urethral stricture — fibrotic narrowing of the urethral lumen, from trauma, instrumentation, or healed infection (classically gonococcal). The physiology that follows is the GU 2 obstruction sequence you already know: raised outlet resistance → detrusor hypertrophy → reduced compliance → incomplete emptying, high residual and infection.
• Where strictures form is anatomical: the fixed, narrow intermediate (membranous) and bulbar segments take the brunt of straddle injury and instrumentation.

• Two jobs, two temperatures. The testis makes sperm (seminiferous tubules, Sertoli cells) and testosterone (Leydig cells). The scrotum keeps it below core temperature — via the pampiniform plexus acting as a countercurrent heat exchanger and the cremaster and dartos muscles adjusting position.
• The processus vaginalis is the key to four diagnoses. It precedes the testis through the inguinal canal; its reflected fold becomes the visceral and parietal layers of the tunica vaginalis, and the connecting canal normally obliterates at or shortly after birth.
• Cryptorchidism — in 97% of male newborns both testes are in the scrotum at birth; most of the rest descend within 3 months; about 1% remain undescended, with a 3–5% incidence of renal anomalies. Undescended testes fail to produce mature spermatozoa. The key qualifier: orchiopexy does not decrease the potential for malignancy — it does facilitate examination and tumor detection.

• The definition: "an abnormal dilation of a vein within the spermatic cord," classically described as a "bag of worms."
• The numbers: occurs in about 10% of males, most often after puberty, and 95% are LEFT-sided.
• Why the left: the left testicular vein drains at a right angle into the left renal vein, at higher pressure and over a longer column; the right drains obliquely straight into the IVC. Note this is the same asymmetry you learned for the ovarian veins in WH 2.
• Two red flags explicitly: the sudden development of a varicocele in an older man is a late sign of RENAL TUMOR; and a unilateral RIGHT-sided varicocele is rare and suggests compression or obstruction of the inferior vena cava by tumor or thrombus.
• Why it matters functionally: the dilated plexus raises testicular temperature and interferes with spermatogenesis — a cause of infertility.

• Hydrocele = fluid within the tunica vaginalis, the closed peritoneal sac left behind by the processus vaginalis. The bedside discriminator: if the testicle is clearly visible and the mass transilluminates, it is a hydrocele.
• Communicating vs non-communicating — the distinction your objective asks for:
  • Communicating — the processus vaginalis remains patent, so peritoneal fluid moves in and out. It therefore changes size with position and activity, is typically congenital, and carries hernia risk because bowel can follow the same path.
  • Non-communicating — the canal is closed; fluid arises from within the sac. The gives the congenital version: irregular obliteration leaves small cysts along the course which later secrete fluid. In adults it follows inflammation, trauma or tumor and is constant in size.
• Spermatocele — a cyst of the epididymis. The algorithm: a mass clearly in the epididymis is an epididymal cyst or spermatocele; a mass within the testis demands scrotal ultrasound plus α-fetoprotein and β-hCG.
• The rule that governs all of them: a mass that does not transilluminate, or is within the testis itself, is a tumor until imaging says otherwise.

• The definition: torsion is "one of several conditions that cause an acute scrotum — testicular pain and swelling — and specifically a condition in which the testis rotates on its vascular pedicle." Torsion "twists the arteries and veins in the spermatic cord."
• The sequence your objective asks for is the same one you learned for the ovary: the twist obstructs the thin-walled veins first → congestion and edema → rising intratesticular pressure → arterial compromise → ischemia → hemorrhagic infarction. The figure shows testes "dark red and partially necrotic owing to hemorrhagic infarction."
• Anatomic and developmental risk factors — the second half of your objective:
  • Bell-clapper deformity — the tunica vaginalis inserts high on the cord rather than anchoring the posterior testis, so the testis hangs free and can rotate. It is usually bilateral, which is why the other side is fixed at surgery.
  • Cryptorchidism — an incompletely descended testis lacks normal fixation.
  • Peak incidence in the neonatal period and around puberty, when rapid testicular growth increases the mass on a mobile pedicle.
• Differentiating the acute scrotum is done based on physical examination and history — a comparison table (the table) covering torsion, epididymitis (, where urinalysis often shows white blood cells) and orchitis.
• The imaging rule: if symptoms have lasted more than 6–8 hours, consider testis scan or color Doppler ultrasound to confirm.

"Fournier" appears in none of them, and has no necrotizing fasciitis section. Written from my own knowledge — verify this one against lecture.

• What it is: a necrotizing fasciitis of the perineal, genital and perianal region — a surgical emergency with high mortality.
• Why it spreads so fast — the mechanism your objective asks for: it is polymicrobial, typically mixed aerobes and anaerobes acting synergistically. The organisms produce enzymes (collagenase, hyaluronidase, heparinase) that dissolve fascial planes and thrombose the small subcutaneous vessels. Thrombosis causes ischemic necrosis of the overlying skin and blocks antibiotic delivery — so the infection outruns both the immune system and the drug.
• The clinical trap: because the destruction runs along fascia beneath apparently viable skin, pain is out of proportion to visible findings early on. Crepitus, dusky skin and systemic toxicity are late.
• Risk factors: diabetes (the strongest), immunosuppression, alcohol use disorder, obesity, and any local breach — perianal abscess, instrumentation, trauma.
• Treatment principle follows the mechanism: antibiotics cannot reach thrombosed tissue, so it is emergent surgical debridement plus broad-spectrum cover — the same logic as the obstructed infected urinary tract in GU 1.

• Cortex outside, medulla inside — two embryologically and functionally different organs in one capsule. The cortex is mesodermal and makes steroids; the medulla is neural crest, a modified sympathetic ganglion, and makes catecholamines.
• The zones, outside — G–F–R makes Salt, Sugar, Sex:
  • Zona glomerulosa — thin, just under the capsule, about 15% of the cortex. The crucial detail: these are the only cells in the adrenal capable of secreting significant aldosterone, because they alone contain aldosterone synthase.
  • Zona fasciculata — the thick middle layer, cortisol (and some androgens).
  • Zona reticularis — inner, adrenal androgens (DHEA, DHEAS) — the layer whose maturation is adrenarche, which you met in WH 1.
• Why the enzyme localization matters: because only the glomerulosa can make aldosterone, and because ACTH controls the fasciculata and reticularis but NOT the glomerulosa (which answers to angiotensin II and potassium), an ACTH problem gives a cortisol problem with preserved aldosterone. That single fact separates primary from secondary adrenal insufficiency.

• Cortisol's headline actions: raises blood glucose by stimulating gluconeogenesis and reducing peripheral glucose use; catabolizes protein everywhere except the liver; mobilizes fatty acids; and is essential for resisting stress and inflammation — a section to that last point.
• The permissive effect: cortisol is required for catecholamines to produce full vasoconstriction — which is why adrenal crisis presents with hypotension refractory to pressors until steroid is given.

• The distinction precisely, and it is a favorite question: Cushing SYNDROME refers to chronic hypercortisolism from any cause. Cushing DISEASE is specifically hypercortisolism caused by excessive ACTH, from a pituitary adenoma. Every Cushing disease is a Cushing syndrome; the reverse is not true.
• Sort the causes by ACTH, because that is what the tests measure:
  • ACTH-dependent — pituitary adenoma (Cushing disease), or ectopic ACTH from a tumor. ACTH is high or inappropriately normal; both adrenals hypertrophy.
  • ACTH-independent — adrenal adenoma, carcinoma, or exogenous glucocorticoid (by far the commonest cause overall). ACTH is suppressed; the contralateral adrenal atrophies.
• Features follow directly from cortisol's actions: hyperglycemia and insulin resistance (gluconeogenesis — and the table lists excess glucocorticoids among the causes of insulin resistance); proximal muscle wasting and thin skin with striae (protein catabolism); central obesity with a moon face and dorsocervical fat pad (fat redistribution); osteoporosis; poor wound healing and infection risk (anti-inflammatory action); and hypertension with hypokalemia via the 11β-HSD2 mechanism above.
• Testing follows the Endo 1 rule — suspect excess, try to SUPPRESS. Dexamethasone suppression; a normal axis suppresses, an autonomous one does not.

• The description: "a small tumor of the zona glomerulosa cells occurs and secretes large amounts of aldosterone" — or hyperplastic cortices secrete aldosterone rather than cortisol. As hyperaldosteronism, , primary or secondary.
• The list of effects, worth memorizing as a set: hypokalemia, mild metabolic alkalosis, a slight increase in extracellular fluid and blood volume, a modest rise in plasma sodium (usually less than 4–6 mEq/L), and almost always hypertension.
• The detail that catches people out: sodium rises only modestly despite massive sodium retention, because water follows it — so the patient is hypertensive and hypokalemic with a nearly normal sodium. Do not expect hypernatremia.
• The clinical vignette: "occasional periods of muscle paralysis caused by the hypokalemia" — a depressant effect of low extracellular potassium on nerve fiber transmission.
• Primary vs secondary in one lab: renin. Primary = autonomous adrenal → renin suppressed. Secondary = the adrenal responding correctly to a renin stimulus (renal artery stenosis, heart failure, cirrhosis) → renin high.

• Addison disease is PRIMARY adrenal insufficiency — the gland itself has failed. secondary insufficiency (from lack of ACTH) is "much more common." adrenocortical hypofunction at.
• Mineralocorticoid deficiency does the damage. lack of aldosterone greatly decreases renal tubular sodium reabsorption, so sodium, chloride and water are lost in the urine — giving greatly decreased extracellular fluid volume and hyponatremia, plus hyperkalemia and mild acidosis because potassium and hydrogen are not secreted in exchange for sodium.
• Glucocorticoid deficiency adds hypoglycemia, weakness, weight loss, and the inability to withstand stress.
• Hyperpigmentation is the sign that localizes the lesion. In primary failure, loss of cortisol feedback drives ACTH sky-high, and ACTH is cleaved from POMC — the same precursor as MSH — so melanocytes are stimulated. Secondary insufficiency has low ACTH, so there is no hyperpigmentation.
• The other discriminator is potassium. Secondary insufficiency spares the glomerulosa, which does not need ACTH — so aldosterone is preserved and the patient is not hyperkalemic and not volume-depleted in the same way. Primary: hyperkalemic and hyperpigmented. Secondary: neither.
• Testing follows the Endo 1 rule — suspect too little, try to STIMULATE. Cosyntropin (ACTH) stimulation.

• The medulla is a sympathetic ganglion that lost its axons. Preganglionic fibers synapse directly on chromaffin cells, which secrete epinephrine (~80%) and norepinephrine into the blood instead of onto a target. Medullary hypofunction at and hyperfunction at .
• Medullary hypofunction is essentially not a clinical problem — the sympathetic nervous system compensates. That asymmetry is worth noticing: you can lose the medulla and be fine, but losing the cortex kills.
• Pheochromocytoma is a catecholamine-secreting tumor of chromaffin cells. The classic triad is episodic headache, palpitations and diaphoresis, on a background of hypertension that is often paroxysmal.
• Why the hypertension is episodic — the tumor releases in bursts, and between bursts chronic catecholamine exposure downregulates adrenoceptors, so the baseline can look near-normal.
• The pharmacological trap worth knowing: block α before β. Giving a β-blocker first removes β₂-mediated vasodilation and leaves α-mediated vasoconstriction unopposed — precipitating a hypertensive crisis.
• Pheochromocytoma in one more place worth noting: in its table of hypercalcemia associations — a pointer toward the MEN syndromes, where pheochromocytoma travels with medullary thyroid carcinoma and hyperparathyroidism.

• The architecture: fetal chorionic villi project into maternal blood sinuses. Fetal capillaries run inside each villus; maternal blood bathes the outside. The two circulations never mix — they are separated by the placental membrane.
• The surface area is surprisingly small — the total villous surface of the mature placenta is only a few square meters, many times less than the pulmonary membrane. Exchange works anyway because the same diffusion physics apply as in the lung.
• Permeability rises through pregnancy. Early on the membrane is thick and the area is small, so conductance is low; both improve steadily until about the last month, when the placenta begins to involute and conductance falls again.
• Maternal placental blood flow is about 625 mL/min in the last month.
• Rupture is rare but real: the membrane can break, letting fetal cells into the mother. Severe fetal hemorrhage into the mother uncommon — but it is the exact event behind Rh sensitization below, and the names the test that quantifies it: the Kleihauer–Betke test, which exploits the different acid resistance of fetal and adult hemoglobin.

• Start with the problem. Maternal PO₂ in the placental sinuses is only about 50 mm Hg, and fetal blood leaving the placenta reaches only about 30 mm Hg. By adult standards that is hypoxic. Three mechanisms rescue it:
• 1 · Fetal hemoglobin (HbF) carries more oxygen at any given PO₂ — its curve is shifted left. HbF has γ chains instead of β, which bind 2,3-BPG poorly — less BPG binding means higher affinity.
• 2 · Fetal hemoglobin CONCENTRATION is about 50% greater than the mother's — this an even more important factor.
• 3 · The DOUBLE Bohr effect. Fetal blood arriving at the placenta is CO₂-rich. CO₂ diffuses out into maternal blood. That makes fetal blood more alkaline (raising its O₂ affinity) and maternal blood more acidic (lowering hers, so she releases O₂). "the Bohr shift operates in one direction in the maternal blood and in the other direction in the fetal blood… therefore it is called the double Bohr effect," and it is twice as important here as in the lungs.
• Total placental diffusing capacity for oxygen at term ≈ 1.2 mL O₂/min/mm Hg.

• The design problem: the fetal lung is fluid-filled and useless for gas exchange, and the fetal liver is immature. So oxygenated blood must bypass both.
• The route, in the order: umbilical vein → ductus venosus (bypassing the liver) → inferior vena cava → right atrium → foramen ovale → left atrium → left ventricle → arteries of the head and forelimbs. Superior vena caval blood (deoxygenated, from the head) is instead directed down through the tricuspid valve → right ventricle → pulmonary artery → ductus arteriosus → descending aorta → umbilical arteries → placenta.
• The flow split: about 55% of the blood pumped by the fetal heart goes through the placenta, leaving only 45% for all fetal tissues. Only 12% goes through the lungs — versus virtually all of it immediately after birth.

• Growth is late-weighted. Organ systems are essentially laid down in the first trimester; the third trimester is when mass is added, which is why prematurity costs weight and reserve rather than organ existence.
• Iron: maternal iron crosses the placenta and about one-third of the fetus's iron is stored in the liver, to be drawn on for months after birth. That store is why exclusive breastfeeding is tolerable for a while and why prematurity predicts iron deficiency.
• Vitamins with specific fetal jobs: B12 and folate for red cells and nervous tissue; vitamin C for bone matrix and connective tissue; vitamin D — needed by the fetus for bone growth but "even more important" for the mother's calcium absorption, with the surplus stored in the fetal liver; vitamin E for early embryonic development.
• Vitamin K and the newborn: vitamin K is added to the mother's diet so the baby has enough prothrombin to prevent hemorrhage — particularly brain hemorrhage — from the birth process. This is the physiology behind the newborn vitamin K injection.
• HCS/hPL is the growth driver from the maternal side — it shifts the mother to fat metabolism and spares glucose for the fetus (WH 4). Fetal growth restriction is therefore usually a supply problem, not a fetal one: placental perfusion, maternal nutrition, or maternal vascular disease. Makes the same point from the other direction — infants of diabetic mothers with vascular disease, hypertension or preeclampsia have IUGR, because limited nutrient delivery compromises the growth of the infant.

• The frequency: about 5% of pregnant women.
• The originating lesion is a FAILURE OF SPIRAL ARTERY REMODELING. Normally "the trophoblasts invade the spiral arteries of the uterine endometrium and completely remodel the maternal arteries into much larger blood vessels with low resistance to blood flow." In preeclampsia "the maternal spiral arteries fail to undergo these adaptive changes… and blood supply to the placenta is insufficient."
• The ischemic placenta then poisons the maternal endothelium. It releases antiangiogenic proteins — soluble Flt-1 (s-Flt1) and soluble endoglin — plus inflammatory cytokines (TNF-α, IL-6). These "impair function of the maternal vascular endothelium and cause hypertension, proteinuria, and the other systemic manifestations."
• The renal signature, and why it is diagnostic: plainly that in preeclampsia renal blood flow and GFR are DECREASED — exactly opposite to the changes that occur in the normal pregnant woman.
• Eclampsia is the same disease with seizures. the definition: "seizures with findings of preeclampsia."

• Management principles worth knowing: magnesium sulfate for seizure prophylaxis once severe preeclampsia is diagnosed and delivery is planned (4–6 g load over 15–20 min, then 2–3 g/h). Treat BP ≥160/110 down to 140–150/90–100 — and note the warning that going lower may induce placental insufficiency through reduced perfusion.
• Safe antihypertensives in pregnancy: labetalol, nifedipine, methyldopa; IV hydralazine in 5–10 mg increments every 20 min acutely. ACE inhibitors, ARBs and mineralocorticoid receptor antagonists are teratogenic and contraindicated.

• The premise: at least 30 common antigens (and hundreds of rare ones) sit on RBC membranes. Only two groups commonly cause transfusion reactions: the O-A-B system and the Rh system.
• Agglutinogens and agglutinins are reciprocal. If you lack the A antigen you develop anti-A agglutinins; if you lack B you develop anti-B. Type O has no agglutinogens but BOTH anti-A and anti-B agglutinins.
• US frequencies O 47%, A 41%, B 9%, AB 3%.
• The consequence: O = universal RBC donor (no antigens to be attacked); AB = universal recipient (no agglutinins to attack). For plasma it inverts — AB plasma is universal, because it contains neither agglutinin.

• Six Rh antigens exist — C, D, E, c, d, e — and each is called an "Rh factor." Type D is the one that matters: widely prevalent and considerably more antigenic than the other Rh antigens. Rh positive means D-positive.
• The critical difference from ABO: Rh agglutinins are NOT spontaneous. An Rh-negative person must first be massively exposed to an Rh antigen before making significant anti-Rh. Anti-Rh agglutinins then develop slowly, peaking 2–4 months later. Hence the first exposure sensitizes; the second one does the damage.
• Prevalence: about 15% of people of European and North American descent, and much lower proportions of African and Asian descent, are Rho(D)-negative. The global figures are ~95% Rh-positive.
• Erythroblastosis fetalis (hemolytic disease of the newborn): the mother is Rh-negative, the father Rh-positive, the baby inherits Rh-positive. The mother makes anti-Rh agglutinins, which cross the placenta and agglutinate the fetus's red cells.
• Why the disease is named as it is: hemolysis drives the liver and spleen to resume making red cells, so many nucleated blastic forms are pushed into the circulation — erythro-blast-osis.
• The clinical picture: anemic at birth, and jaundiced because macrophages convert released hemoglobin to bilirubin. Maternal agglutinins persist in the infant for another 1–2 months, destroying more cells.
• When sensitization happens — the list: fetal red cells enter the maternal circulation "during small fetomaternal bleeding episodes in the early third trimester or during delivery, abortion, ectopic pregnancy, placental abruption, or other instances of antepartum bleeding. Once produced, the antibody remains in the mother's circulation and poses the threat of hemolytic disease for subsequent Rh-positive fetuses."

• The origin is embryonic. Primordial germ cells migrate into the testes and become spermatogonia, sitting in two or three layers on the inner surface of the seminiferous tubules. They stay dormant until puberty, when they begin mitotic division.
• The sequence to memorize, with the own cell divisions:
  • Spermatogonium — proliferates by mitosis (self-renewing, so the supply never runs out)
  • → Primary spermatocyte (diploid) — crosses into the Sertoli cell layer and enlarges
  • → meiosis I → two secondary spermatocytes
  • → meiosis II (a few days later) → spermatids
  • → spermiogenesis (differentiation, no division) → spermatozoa
• Direction of travel: spermatogonia migrate among the Sertoli cells toward the central lumen, whose cytoplasm surrounds them the whole way. So the sequence is also a map: earliest cells at the basement membrane, most mature at the lumen.
• The number to know: the entire process takes about 74 days. That is why a toxic insult (fever, chemotherapy, heat) shows up in the semen 2–3 months later, and why any fertility intervention needs at least that long to be judged.
• Maturation happens after the testis. Sperm need several days to traverse the 6-meter epididymal tubule. Sperm taken from the seminiferous tubules or early epididymis are non-motile and cannot fertilize; after 18–24 hours in the epididymis they gain the capability of motility, though inhibitory proteins hold it back until ejaculation.
• Output: the two testes form up to 120 million sperm per day.

• Why the blood–testis barrier exists: meiosis creates haploid cells the immune system has never seen — they first appear long after self-tolerance is established. Isolate them, or they get attacked. Break the barrier (trauma, vasectomy, mumps orchitis) and antisperm antibodies can follow.
• The full list of hormones required for spermatogenesis — worth reading as a checklist of ways it can fail: testosterone (germinal cell growth), LH (drives Leydig testosterone), FSH (drives Sertoli cells; without it spermiogenesis fails), estrogens from Sertoli cells, and growth hormone for background metabolic function — "in its absence, as in pituitary dwarfs, spermatogenesis is severely deficient or absent, thus causing infertility."

• The statement of the axis: feedback is via "(1) testosterone, which can inhibit hypothalamic GnRH secretion and pituitary LH responsiveness to GnRH; and (2) testicular inhibin that inhibits pituitary FSH and, possibly, circulating estrogens. And then the sentence that frames the whole lecture: Any disruption along the H-P-T axis may lead to hypogonadism or infertility."
• GnRH is pulsatile, and the pulsatility is the signal — continuous GnRH downregulates the pituitary rather than stimulating it, which is exactly how GnRH agonists are used to achieve androgen deprivation in prostate cancer (GU 3). Same molecule, opposite effect, purely because of timing.
• Contrast with the female axis (WH 1): the male axis is a pure negative-feedback loop with no positive-feedback surge. There is no LH surge because there is nothing to ovulate — sperm production is continuous rather than cyclical.

• The three-nerve version of Point and Shoot: Parasympathetic = Point, Sympathetic = Shoot (emission), Somatic = the final Squirt. Your objective explicitly asks you to differentiate all three.

• The chain: parasympathetic fibers release nitric oxide → NO activates guanylyl cyclase → cGMP rises → trabecular smooth muscle of the cavernous sinusoids relaxes → sinusoids fill and compress the subtunical veins → erection.
• PDE5 degrades cGMP, ending the signal. PDE5 inhibitors (sildenafil, tadalafil) block that degradation — they do not generate cGMP, so they require intact parasympathetic NO release. That is why they fail after radical prostatectomy with nerve injury, and why they fail without arousal.
• Testosterone's role is upstream and permissive: it maintains libido and supports NO synthase expression in cavernous tissue. So hypogonadism blunts both desire and the erectile response — but replacing testosterone in a man with normal levels does not improve erections, because the deficit is not there.
• The dangerous interaction: PDE5 inhibitors plus nitrates (which are NO donors) stack two steps of the same pathway and can cause profound hypotension. Absolute contraindication.

• The framework — spermatogenesis requires adequate FSH and LH, sufficient Leydig testosterone, sufficient Sertoli function (androgen-binding protein, growth factors, inhibin B), and adequate spermatogonia. Remove any one and fertility falls.
• Inadequate gonadotropin secretion may be caused by hypothyroidism, hyperadrenocortisolism, hyperprolactinemia, or hypogonadotropic hypogonadism — gonadotropins are low because of feedback inhibition or idiopathic hyposecretion. Note that three of those four are endocrine problems you have already studied — this objective is a payoff for Endo 2, 4 and 5.
• Defects in TESTICULAR RESPONSE give the mirror pattern: decreased testosterone and inhibin B, and therefore — by normal feedback — HIGH circulating gonadotropins.
• Sperm count: average ejaculate ~3.5 mL containing about 120 million sperm/mL (normal range 35–200 million). "When the number of sperm in each milliliter falls below about 20 million, the person is likely to be infertile."
• Structural and anatomical causes you already know: varicocele (raised testicular temperature — GU 4), cryptorchidism (undescended testes fail to produce mature spermatozoa — GU 4), obstruction (post-infectious epididymal scarring, vasectomy), and Klinefelter syndrome, which in the workup of delayed puberty.
• The note on cryptorchidism is subtler than it looks: "many, if not most, cases of cryptorchidism are caused by abnormally formed testes that are unable to secrete enough testosterone" — so the surgery is unlikely to be successful in those patients. The undescent is a symptom of a bad testis as often as it is the cause of one.

• The causes of ED, verbatim: neurologic, vascular, endocrine, and psychological, rising sharply with age. Your objective names five categories — map them:
• Ageing: gradual decline in testosterone and in NO-mediated vasodilation; longer refractory period; reduced libido. Unlike menopause, it is gradual and incomplete — spermatogenesis continues into old age.
• Cardiovascular disease: the dominant organic cause. Endothelial dysfunction is endothelial dysfunction wherever it occurs — and because penile arteries are small, they declare it first. ED is a predictor of coronary events, not merely a consequence.
• Endocrine: hypogonadism (low desire and low NOS), hyperprolactinemia (suppresses GnRH — connects straight to Endo 5), thyroid disease, diabetes (both autonomic neuropathy and vascular disease, which is why diabetic ED is often the hardest to treat).
• Medications: antihypertensives (especially thiazides and non-selective β-blockers), SSRIs (delayed ejaculation and reduced desire), antiandrogens and 5α-reductase inhibitors (GU 3), α-blockers (retrograde ejaculation rather than ED), alcohol and opioids.
• Psychological: the discriminator worth knowing is preserved nocturnal and early-morning erections, which indicate the machinery works and point to a psychogenic or situational cause.

• Anterior pituitary (adenohypophysis) originates from Rathke pouch, "an ectodermal evagination of the oropharynx," which migrates up to join the neurohypophysis. Remnants of Rathke pouch may persist and form colloid cysts — and, left lower down, the origin of craniopharyngioma.
• Posterior pituitary (neurohypophysis) is NOT A GLAND. it is "only the distal axon terminals of the hypothalamic magnocellular neurons." The cell bodies sit in the paired supraoptic and paraventricular nuclei of the hypothalamus.
• So the two lobes are controlled completely differently:
  • Anterior: controlled hormonally, by releasing and inhibitory hormones carried down the hypothalamic–hypophysial portal vessels.
  • Posterior: controlled neurally — the hormone is made in the hypothalamus and simply transported down the axon and stored.
• Anterior cell types, named by product — the replacement for the old acidophil/basophil/chromophobe scheme: somatotrophs (GH), lactotrophs (PRL), thyrotrophs (TSH), corticotrophs (ACTH), gonadotrophs (LH and FSH). Lineage is set by transcription factors — notably Prop1 and Pit1 — and abnormalities in these "have been associated with the development of hypopituitarism."
• Posterior hormones: vasopressin (ADH) and oxytocin, both nonapeptides, synthesized as larger precursors with a neurophysin carrier and — for vasopressin only — a glycopeptide called copeptin. Granules travel down the axon; peptidases cleave the prohormone en route.

• The description of the portal system: hypothalamic releasing and inhibitory hormones are "conducted… to the anterior pituitary through minute blood vessels called hypothalamic-hypophysial portal vessels," where they act on the glandular cells.
• Why a PORTAL system at all? It delivers hypothalamic hormones to the pituitary in high local concentration without diluting them in the systemic circulation. Nanogram quantities suffice. It also means cutting the stalk cuts the signal — which is the anatomical basis of stalk effect below.
• The hypothalamus is where the nervous and endocrine systems meet. receives pain signals, emotional signals, and olfactory input — which is the mechanism behind stress-, exercise- and emotion-driven endocrine change.
• Three-tier architecture (from Endo 1): hypothalamus → pituitary → target gland → hormone → long-loop negative feedback on both upper tiers. Short-loop feedback runs pituitary → hypothalamus.

• GH is diabetogenic — the word. Excess GH can produce metabolic disturbances similar to those found in patients with type 2 diabetes. His clinical discriminator is elegant: acromegalic patients are usually LEAN with little visceral fat, whereas type 2 diabetics are usually overweight with excess visceral fat driving the resistance. The proposed mechanism is GH-driven lipolysis raising free fatty acids, which impairs insulin's action on liver and muscle.

• The rule: "Hyperpituitarism generally is caused by a pituitary adenoma," and anterior hypofunction results from infarction, removal or destruction, or space-occupying lesions — adenomas or aneurysms — that compress normal secreting cells.
• The number that changes how you read an MRI report: 10% to 20% of the general population harbor non-functional, asymptomatic pituitary microadenomas, and that patients with microadenomas "may have normal neuroradiologic studies." So diagnosis "should be based on both endocrine and radiologic criteria."
• Micro vs macro: <10 mm = microadenoma (usually presents by hormone excess); ≥10 mm = macroadenoma (presents by mass effect as well).
• Mass effect is anatomical. "the optic chiasm lies 5 to 10 mm above the diaphragma sellae and anterior to the stalk, and the lateral walls of the sella are in direct apposition to the cavernous sinuses." Upward growth therefore compresses the chiasm — bitemporal hemianopia, because the crossing fibers from the nasal retinae carry the temporal visual fields. Lateral growth invades the cavernous sinus and can take out CN III, IV, V₁, V₂ and VI.
• The ordering detail: GH-secreting cells are the most sensitive to pressure — so GH is typically the first axis lost when a mass compresses the gland.

• Causes infarction of the gland, removal or destruction, or compression by adenoma or aneurysm. Functional hypopituitarism is seen in anorexia nervosa; starvation; or severe, systemic illness — a real distinction, because that version is reversible.
• The adult causes: craniopharyngiomas or chromophobe tumors compressing the gland to destruction, or thrombosis of the pituitary blood vessels.
• The warning about tempo: "the clinical features of hypopituitarism are often subtle, and years may pass before pituitary insufficiency is recognized following an ischemic insult."
• The classic order in which axes fail with progressive compression: GH → gonadotropins → TSH → ACTH → prolactin. supports the first step directly (GH-secreting cells are most sensitive to pressure). The practical point: ACTH is lost last but matters most — and when you replace hormones, give glucocorticoid BEFORE thyroxine, because thyroxine raises metabolic demand and can precipitate adrenal crisis in someone who is also cortisol-deficient.
• Sheehan syndrome — postpartum pituitary necrosis. The mechanism is a payoff from WH 4: the pituitary hypertrophies during pregnancy (lactotroph expansion) without a matching rise in its blood supply, so it is uniquely vulnerable to peripartum hemorrhage and hypotension. Classically presents as failure to lactate, then amenorrhea.

• Vasopressin is the water-retaining hormone in all mammals and, along with thirst, the primary regulator of osmolality.
• Osmoreceptors are exquisitely sensitive; baroreceptors are not. the figure shows osmoreceptor response to as little as a 1% change in osmolality, whereas volume or pressure must fall by 10–15% before plasma vasopressin measurably rises.
• The whole dynamic range of urine concentration is covered by a tiny hormone range — maximally dilute to maximally concentrated urine spans a plasma vasopressin of roughly 1 to 5 pg/mL.
• The renal mechanism — ADH binds membrane receptors → adenylyl cyclase → vesicles carrying aquaporin water pores insert into the luminal membrane of the collecting duct. Without ADH those membranes are "almost impermeable to water," giving "extreme dilution of the urine, a condition called central diabetes insipidus."

• The four causes of polyuria, which is the cleanest way to hold the DI differential: (1) primary ingestion of excess fluid — primary polydipsia; (2) abnormally decreased synthesis and secretion of vasopressin — hypothalamic (central) DI; (3) increased metabolism of vasopressin — the mechanism of gestational DI, since placental vasopressinase accelerates clearance; (4) decreased end-organ response — nephrogenic DI.
• Why DI hides until it is severe — the sentence worth quoting: "considerable loss of ability to secrete vasopressin can occur before there is much loss of ability to concentrate the urine, and even greater loss before there is a noticeable increase in urine volume." The complaint is volume, not concentration.
• Gestational DI in the words: a patient with pre-existing partial hypothalamic DI or mild nephrogenic DI may be adequate before pregnancy, but "during pregnancy the metabolism of vasopressin is accelerated" and she manifests DI — which resolves when the pregnancy ends. This is a WH 5 crossover.
• Diagnosis: water deprivation test — if urine fails to concentrate, DI is confirmed; then give desmopressin. Central DI concentrates the urine; nephrogenic DI does not. Primary polydipsia concentrates with deprivation alone. Copeptin assays are replacing this.
• SIADH diagnostic caveat explicitly: to diagnose SIADH the individual must have normal adrenal and thyroid function — because hypothyroidism and adrenal insufficiency both cause hyponatremia and would otherwise be mistaken for it.
• SIADH causes worth having: small cell lung carcinoma (ectopic ADH), CNS disease (stroke, hemorrhage, meningitis), pulmonary disease (pneumonia), drugs (SSRIs, carbamazepine, cyclophosphamide), and pain, nausea and the postoperative state.

• With the job description — the alimentary tract supplies water, electrolytes, vitamins and nutrients, and doing that requires four things: (1) movement of food, (2) secretion of digestive juices and digestion, (3) absorption, (4) circulation of blood to carry away what was absorbed — all controlled by nervous and hormonal systems. Every GI disease in the course is a failure of one of those four.
• The wall, outside in: serosa → longitudinal muscle → circular muscle → submucosa → mucosa, plus sparse muscularis mucosae in the deeper mucosa.
• GI smooth muscle behaves as a SYNCYTIUM. Fibers are 200–500 µm long and connected by gap junctions, so an electrical signal spreads through a whole sheet rather than firing one cell. That is why the gut contracts in rings and waves rather than in twitches.
• The two muscle layers do different jobs: circular muscle narrows the lumen (the contractile ring of peristalsis), longitudinal muscle shortens the segment. Both are needed — the ring pushes, the shortening pulls the bowel over the bolus.

• Two kinds of electrical activity, and they do different things. Slow waves are undulating changes in resting membrane potential — they are NOT action potentials and mostly do not themselves cause contraction. Spike potentials are true action potentials, and they are what actually excites contraction.
• The pacemaker is the interstitial cells of Cajal — specialized cells forming a network interposed between the smooth muscle layers, with synapse-like contacts onto muscle. They undergo cyclic membrane-potential changes via unique ion channels that produce inward pacemaker currents.
• Slow-wave frequencies you should know: stomach ~3/min, duodenum ~12/min, ileum 8–9/min.
• The threshold rule: resting potential is −50 to −60 mV; spike potentials appear whenever a slow-wave peak rises above about −40 mV. The higher the slow-wave peak, the more spikes and the stronger the contraction — 1 to 10 spikes/second.
• What moves the baseline: DEPOLARIZING (more excitable) — stretch, acetylcholine, parasympathetic stimulation. HYPERPOLARIZING (less excitable) — norepinephrine, sympathetic stimulation.

• The gut has its own brain. the enteric nervous system can function independently of extrinsic nerves, though sympathetic and parasympathetic stimulation can greatly enhance or inhibit its output.
• Two plexuses, two jobs — and this pairing is examined constantly:
  • Myenteric (Auerbach's) plexus — lies between the longitudinal and circular muscle layers; controls mainly gastrointestinal MOVEMENT.
  • Submucosal (Meissner's) plexus — lies in the submucosa; controls mainly SECRETION and local blood flow.
  Myenteric = Movement (both start with M, and it sits in the muscle). Submucosal = Secretion (both start with S).
• Neurotransmitters: more than 25, but the two rules that matter are simple — acetylcholine most often EXCITES GI activity; norepinephrine almost always INHIBITS it, as does adrenal epinephrine arriving via the blood. Also on the list and worth noting: vasoactive intestinal polypeptide (VIP) and nitric oxide — the inhibitory transmitters whose loss defines achalasia.
• Extrinsic control follows the general autonomic logic: parasympathetic (vagus above the splenic flexure, pelvic nerves below) = rest and digest = increased motility and secretion. Sympathetic = fight or flight = inhibited motility, constricted sphincters, reduced blood flow. That is also why sympathetic surge from pain, surgery or shock produces an ileus.

• Muscle type changes down its length — 's: the esophageal muscle coat is striated in the upper two-thirds and innervated by the vagus, and smooth in the lower third, innervated by the splanchnic plexus. That anatomy is why stroke, myasthenia and muscular dystrophy cause OROPHARYNGEAL dysphagia (striated muscle, voluntary phase), whereas achalasia and scleroderma cause ESOPHAGEAL dysphagia (smooth muscle).
• The three stages of swallowing: voluntary (bolus pushed into the pharynx) → pharyngeal (involuntary; the airway is closed and the upper sphincter opens) → esophageal (transport).
• Swallowing takes priority over breathing. "The swallowing center specifically inhibits the respiratory center of the medulla during this time, halting respiration at any point in its cycle."
• Two kinds of esophageal peristalsis:
  • PRIMARY — a continuation of the pharyngeal wave. Reaches the stomach in 8–10 seconds, or 5–8 seconds upright because gravity helps.
  • SECONDARY — triggered by distension of the esophagus by retained food when primary peristalsis fails. Continues until the esophagus empties. Generated partly by the myenteric plexus itself — which is why, even after paralysis of the brain stem swallowing reflex, food fed by tube… still passes readily into the stomach.
• Receptive relaxation runs ahead of the wave. A wave of relaxation carried by myenteric inhibitory neurons precedes the peristaltic wave, relaxing not only the sphincter but the whole stomach and even the duodenum, so they are prepared to receive the bolus.
• The lower esophageal sphincter is not a discrete muscle but the circular muscle of the last ~3 cm, tonically constricted at an intraluminal pressure of about 30 mm Hg, while the mid-esophagus stays relaxed.

• The bedside question that sorts them: difficulty with solids only, progressing to liquids suggests a mechanical narrowing (the lumen is shrinking). Difficulty with solids AND liquids from the start suggests a motility problem — the pump is broken, and liquids need a working pump just as much.

• The definition: "a condition in which the lower esophageal sphincter fails to relax during swallowing," so swallowed food fails to pass into the stomach.
• The lesion is neural, not muscular. pathophysiological studies show damage in the neural network of the myenteric plexus in the lower two-thirds of the esophagus, so the musculature "remains spastically contracted" and the plexus "has lost its ability to transmit a signal to cause 'receptive relaxation'. and adds the histology: a decrease in the number of myenteric ganglion cells and atrophy of smooth muscle cells."
• The three mechanisms that impair swallowing — worth listing separately, because it is more than just a tight sphincter: (1) decreased peristalsis of the middle esophagus, (2) loss of tone in the LES, (3) decreased relaxation of the LES after swallowing.
• Why it dilates: food accumulates above the obstruction and distends the esophagus; as hydrostatic pressure rises, food is slowly forced past the obstruction. When severe, the esophagus cannot empty for many hours instead of the normal few seconds, and over months it dilates enormously — megaesophagus.
• Treatments follow the mechanism — mechanical dilation of the sphincter and myotomy, a longitudinal incision that widens the passage. Botulinum toxin works for the same reason atropine blocks peristalsis: the residual tone is cholinergic.

• Physiologic vs pathologic: the LES "may relax spontaneously and transiently 1 to 2 hours after eating," and the acid is normally neutralized and cleared by peristalsis within 1 to 3 minutes. Reflux that causes no symptoms is physiologic reflux; when a combination of factors produces an inflammatory response, it is reflux esophagitis.
• The mechanism: "Normally the resting tone of the LES maintains a zone of high pressure that prevents gastro-esophageal reflux. In individuals who develop reflux esophagitis, this pressure tends to be lower than normal." Anything raising abdominal pressure — vomiting, coughing, lifting, bending — overcomes it.
• Clinical manifestations: heartburn, regurgitation of acidic chyme, upper abdominal pain within 1 hour of eating, worse lying down or with raised intra-abdominal pressure. Note the caveat: "symptoms may be present when no acid is in the esophagus."
• The tissue consequences, in sequence: hyperemia → increased capillary permeability → edema → tissue fragility → erosion and ulceration, with fibrosis, basal cell hyperplasia and elongated papillae. "Precancerous lesions (Barrett esophagus) can be a long-term consequence."
• Complications you can derive from that sequence: fibrosis → stricture → mechanical dysphagia; Barrett = intestinal metaplasia, squamous epithelium replaced by columnar because columnar tolerates acid better — an adaptation that becomes a cancer risk (adenocarcinoma of the distal esophagus).
• Management follows the pressure logic: antacids neutralize; elevating the head of the bed 6 inches uses gravity; weight reduction and stopping smoking reduce abdominal pressure and raise sphincter tone; proton pump inhibitors are more effective than H₂ blockers or prokinetics for severe disease; laparoscopic fundoplication is the commonest surgical treatment.

• Definition: a hiatal hernia is a type of diaphragmatic hernia — "the protrusion of the upper part of the stomach through the diaphragm and into the thorax."

• The embryology behind the congenital versions — 's: the stomach begins as a fusiform dilation of the foregut in the primitive thoracic region, and "growth to lengthen the esophageal region is essential for positioning the stomach in the abdominal cavity below the diaphragm."
  • If that lengthening does not occur at all → diaphragmatic hernia, with the stomach remaining in the thorax and compressing the lungs (hence the pulmonary hypoplasia that kills these babies).
  • If the esophagus fails to lengthen sufficiently → the stomach is pulled up into the esophageal hiatus → congenital hiatal hernia.
• Esophageal atresia and tracheo-esophageal fistula — the other foregut defect worth knowing, because it comes from the same partition. The tracheo-esophageal septum divides the foregut into a ventral respiratory primordium and a dorsal esophagus; the defect "results either from spontaneous posterior deviation of the tracheo-esophageal septum or from some mechanical factor pushing the dorsal wall of the foregut anteriorly." In its commonest form (90%) the proximal esophagus ends as a blind sac and the distal part connects to the trachea just above the bifurcation.
• Why atresia causes polyhydramnios: the fetus cannot swallow amniotic fluid. Compare WH 5 — fluid volume depends on fetal swallowing and urination, so a proximal GI obstruction gives POLYhydramnios and a renal/urinary problem gives OLIGOhydramnios.

• Start from the pressure. Portal venous pressure is normally 3 mm Hg; portal hypertension is a rise to at least 10 mm Hg.
• The anatomy that makes it possible: the portal veins carry blood from the GI tract, pancreas and spleen to the liver, through the sinusoids, into the hepatic veins and then the inferior vena cava. Those three components are the portal venous system.
• Portal hypertension is caused by anything that obstructs or impedes flow through any part of that system — within the liver by "thrombosis, inflammation, or fibrosis of the sinusoids, as occurs in cirrhosis, viral hepatitis, or schistosomiasis"; or by hepatic vein thrombosis obstructing outflow.
• Varices are the escape route. When portal pressure exceeds caval pressure, blood is shunted through collateral veins connecting the portal and caval systems — the figure names them: esophageal (via the coronary/left gastric and azygos), short gastrics, veins of Sappey (periumbilical), and hemorrhoidal. Those collaterals are thin-walled and submucosal, so they bleed.
• The other three consequences of portal hypertension, from the same figure: ascites — hydrostatic pressure forces water out of these vessels and into the peritoneal cavity (a transudative effusion); hepatic encephalopathy — because blood that is shunted through collateral vessels to the systemic circulation bypasses hepatic detoxification; and jaundice and hepatorenal syndrome.
• Varices sit at the top of the UPPER GI bleeding list, alongside bleeding ulcer and Mallory-Weiss tear.
• Why the BUN rises in an upper GI bleed — the own chain, and a favorite question: blood in the gut is digested as protein, raising blood urea nitrogen. So a raised BUN with a normal creatinine points upstream.

• Gross organization, outside in: fibrous renal capsule → cortex → medulla, which is arranged into pyramids. Renal columns of cortex extend down between the pyramids; the apex of each pyramid projects into a minor calyx, which joins to form major calyces and then the renal pelvis.
• The nephron is the functional unit — glomerulus in Bowman capsule (together the renal corpuscle) → proximal convoluted tubule → loop of Henle (descending and ascending limbs) → distal tubule → collecting duct.
• Mesangial cells sit between and support the glomerular capillaries. They are contractile and phagocytic, like monocytes, and produce vasoactive substances that influence filtration. That is why they are central to glomerulonephritis — a contractile, phagocytic, immune-active cell inside the filter.

• Read the table as a strategy, not a list. The proximal tubule is bulk reclamation — it takes back most of everything, unregulated. The loop builds the medullary gradient, which is the tool. The distal tubule and collecting duct are fine control — and they are the only segments that answer to hormones (aldosterone, ADH, PTH). Diuretics that act proximally are weak because distal segments compensate; loop diuretics are powerful because they destroy the gradient everything downstream depends on.

• The numbers to hold: GFR ≈ 125 mL/min = 180 L/day. Filtration fraction ≈ one-fifth — normally, about one-fifth of the fluid in the glomerular capillaries filters into Bowman's capsule.
• Filtration is Starling forces applied to a capillary with an arteriole at BOTH ends — that is the whole trick of the glomerulus. Constricting the afferent arteriole reduces both flow and GFR; constricting the efferent arteriole raises glomerular pressure and GFR while reducing flow.
• Filtering concentrates the protein left behind. because about a fifth of the plasma filters out, the plasma proteins that do not filter become concentrated, raising glomerular colloid osmotic pressure along the capillary and progressively opposing further filtration. Raising the filtration fraction concentrates them more and self-limits GFR.
• Autoregulation via tubuloglomerular feedback: the kidney "links changes in the sodium chloride concentration at the macula densa with the control of renal arteriolar resistance." The purpose is "to ensure a relatively constant delivery of sodium chloride to the distal tubule" — so GFR is sometimes autoregulated at the expense of renal blood flow.
• Renin release — the three triggers, worth memorizing as a set: (1) decreased blood pressure in the afferent arteriole, which reduces stretch of the juxtaglomerular cells; (2) decreased NaCl concentration in the distal convoluted tubule; and (3) sympathetic stimulation of β-adrenergic receptors on the juxtaglomerular cells. The third trigger is why β-blockers lower renin.
• Pressure natriuresis: raising arterial pressure increases renal excretion of salt and water — this crucial in the regulation of body fluid volumes and arterial pressure. It is the long-term controller of blood pressure, and it means sustained hypertension requires a kidney that has reset it.
• The kidney's non-excretory jobs — them under renal hormones: activation of vitamin D (Endo 1 — the 1α-hydroxylation step PTH drives) and production of erythropoietin. This is why chronic kidney disease gives anemia and renal bone disease, not just uremia.

• Three kidney systems, cranial to caudal, overlapping:
  • Pronephros — week 4, 7–10 solid cell groups in the cervical region forming vestigial nephrotomes. "Rudimentary and non-functional"; gone by the end of week 4.
  • Mesonephros — "may function for a short time during the early fetal period."
  • Metanephros — "forms the permanent kidney," from the ureteric bud plus the metanephric mesoderm.
• The interaction that makes a kidney is reciprocal induction: GDNF produced by the metanephric mesoderm produces branching and growth of the ureteric bud. Mutations in genes regulating GDNF signaling cause renal hypoplasia or agenesis — the names SALL1 (Townes–Brocks), PAX2 (renal coloboma syndrome) and EYA1 (branchio-oto-renal syndrome). This is the "genetic contribution" your objective asks for.
• The kidney ASCENDS, and the ascent explains almost every anomaly. It starts in the pelvis and moves cranially, driven by diminution of body curvature and by growth of the body in the lumbar and sacral regions. Along the way it is vascularized by successively higher aortic branches; the lower ones usually degenerate — but some persist, which is the origin of accessory renal arteries.

• Both PKDs are ciliopathies — "linked to mutations in genes that encode proteins localized in cilia" and important for ciliary function. The tubular cilium senses flow; lose that sensing and the tubule cannot judge its own diameter, so it dilates into a cyst. That is also why ADPKD comes with extrarenal cysts (liver, pancreas) and berry aneurysms — cilia are everywhere.

• The compartment figures for a 70 kg adult: total body water ≈ 60% of body weight (42 L), split into intracellular ≈ 40% (28 L) and extracellular ≈ 20% (14 L). The ECF further splits into interstitial ≈ 11 L and plasma ≈ 3 L.
• The blood numbers: blood volume is about 7% of body weight, or 5 liters; about 60% of blood is plasma and 40% red cells. Measured hematocrit is normally about 0.40 in men and 0.36 in women.
• Blood volume = plasma volume ÷ (1 − hematocrit) — the worked example: 3 L plasma at a hematocrit of 0.40 gives 5 L total.
• Osmosis is the only way water moves. for each milliosmole gradient of an impermeant solute, about 19.3 mm Hg of osmotic pressure is exerted across the cell membrane — and if a cell at 282 mOsm/L were placed in pure water the potential pressure would exceed 5400 mm Hg. Small changes in extracellular impermeant solute cause large changes in cell volume.
• Isotonic / hypotonic / hypertonic: a cell in a solution of impermeant solutes at 282 mOsm/L neither shrinks nor swells.
• The two-variable rule that runs the whole subject: SODIUM determines where water goes; WATER determines the sodium concentration. Total body sodium sets ECF volume (edema vs dehydration, controlled by aldosterone and pressure natriuresis). Total body water sets serum sodium concentration (controlled by ADH and thirst). So a serum sodium is a water report, not a sodium report — which is why hyponatremia occurs in fluid overload and hypernatremia in a dehydrated patient with a normal total body sodium.
• The hormones, in one place: ADH → water (Endo 5); aldosterone → sodium retention and potassium secretion (Endo 4); ANP/BNP and urodilatin → natriuresis and diuresis, opposing the other two; angiotensin II → efferent constriction, sodium reabsorption, aldosterone and thirst.

• Each day the body makes about 80 mEq of NONVOLATILE acid, mainly from protein metabolism. They are "nonvolatile because they are not H₂CO₃ and therefore cannot be excreted by the lungs" — renal excretion is the primary route.
• 1 · BUFFERS — instantaneous. The bicarbonate buffer system is quantitatively the most important in the extracellular fluid: a weak acid (H₂CO₃) and a bicarbonate salt (NaHCO₃). CO₂ + H₂O ⇌ H₂CO₃ is slow unless carbonic anhydrase is present — and it is abundant in lung alveolar walls and renal tubular epithelium, i.e. Exactly the two organs that regulate acid–base.
• Why the bicarbonate system works despite a bad pK. Its pK is 6.1, well away from a pH of 7.4 — normally a poor buffer. It dominates anyway because both of its components are independently regulated: CO₂ by the lungs, HCO₃⁻ by the kidneys. It is an open system.
• The Henderson–Hasselbalch equation, in the final form:
  pH = 6.1 + log ( HCO₃⁻ ÷ (0.03 × PCO₂) )
  Read it as a ratio. pH depends on HCO₃⁻ over PCO₂ — the numerator is metabolic/renal, the denominator is respiratory. Every acid–base disorder and every compensation is an attempt to protect that ratio.
• Buffers work together: "any condition that changes the balance of one of the buffer systems also changes the balance of all the others, because the buffer systems actually buffer one another by shifting H⁺ back and forth." The other buffers are phosphate (important in tubular fluid and intracellularly), proteins (the largest intracellular buffer), and bone in chronic acidosis.
• 2 · RESPIRATORY — minutes. "The second line of defense… is control of extracellular fluid CO₂ concentration by the lungs." Increased ventilation removes CO₂ and lowers H⁺; decreased ventilation raises both. Normal PCO₂ is 40 mm Hg, corresponding to about 1.2 mmol/L dissolved CO₂.
• The respiratory response is a feedback loop, and it is asymmetric. Alveolar ventilation rises four to five times normal as pH falls from 7.4 to 7.0 — but the response to alkalosis is much weaker, because you can only slow breathing so far before hypoxia forces you to breathe again.
• 3 · RENAL — hours to days, but the only one that ELIMINATES acid. The kidney has two tasks: reabsorb the filtered bicarbonate and excrete the nonvolatile acid. The first is "quantitatively more important" — the kidneys filter about 4320 mEq of HCO₃⁻ per day (180 L × 24 mEq/L) and reabsorb nearly all of it.

• The definitions, exactly: disorders from "a primary change in extracellular fluid HCO₃⁻ concentration" are metabolic; acidosis from a primary decrease in HCO₃⁻ is metabolic acidosis, alkalosis from a primary increase is metabolic alkalosis. "Acidosis caused by an increase in PCO₂ is called respiratory acidosis, whereas alkalosis caused by a decrease in PCO₂ is termed respiratory alkalosis."

• The rule that makes the table unnecessary: in a primary disorder, pH and the primary variable move in the direction that explains the pH. In compensation, HCO₃⁻ and PCO₂ move in the SAME direction as each other — because compensation is always an attempt to restore the ratio, not to oppose it. If HCO₃⁻ and PCO₂ are moving in opposite directions, you are looking at two primary disorders, not compensation.
• Compensation never fully corrects. If the pH is back to exactly 7.40, suspect either a mixed disorder or that you are looking at a chronic process with a second one on top. The body settles for "less abnormal," not "normal."

the physiology; the algorithm is convention. Normal values: pH 7.35–7.45 · PCO₂ 35–45 mm Hg · HCO₃⁻ 22–26 mEq/L.

• Step 1 — Is it acidemic or alkalemic? Look at pH alone. Below 7.35 = acidemia; above 7.45 = alkalemia. If pH is normal but PCO₂ or HCO₃⁻ is not, suspect a mixed or fully compensated picture.
• Step 2 — Which variable explains it? Ask which one has moved in the direction that would cause the observed pH. Acidemia with a high PCO₂ = respiratory. Acidemia with a low HCO₃⁻ = metabolic. Alkalemia with a low PCO₂ = respiratory. Alkalemia with a high HCO₃⁻ = metabolic.
• Step 3 — Is the compensation appropriate? Not merely present — appropriate in size. This is where most marks are lost.
  • Metabolic acidosis → Winter's formula: expected PCO₂ = 1.5 × HCO₃⁻ + 8 (± 2). If measured PCO₂ is higher than expected, there is an additional respiratory acidosis; if lower, an additional respiratory alkalosis.
  • Metabolic alkalosis: PCO₂ rises about 0.7 mm Hg for every 1 mEq/L rise in HCO₃⁻.
  • Acute respiratory: HCO₃⁻ moves about 1 mEq/L per 10 mm Hg change in PCO₂. Chronic respiratory: about 4 mEq/L per 10 mm Hg — because the kidney has had time. The size of the bicarbonate response tells you how long it has been going on.
• Step 4 — If there is a metabolic acidosis, calculate the ANION GAP: Na⁺ − (Cl⁻ + HCO₃⁻), normal 8–12 mEq/L. A raised gap means an unmeasured anion has been added (this is Ren 2's objective, but the calculation belongs here). Correct for albumin — add about 2.5 to the expected gap for every 1 g/dL the albumin is below 4, or a hypoalbuminemic patient's real gap will be missed.
• Step 5 — Does the picture fit the patient? An ABG that does not match the history is usually a clue to a second process, not a laboratory error.

• Functional divisions: cardia → fundus → body → antrum → pylorus. Also splits it physiologically into an orad portion (storage) and a caudad portion (mixing and emptying).
• Two gland types, and their territories are the key fact:
  • Oxyntic (gastric) glands — on the inside surfaces of the body and fundus, i.e. The proximal 80% of the stomach. They secrete hydrochloric acid, pepsinogen, intrinsic factor and mucus.
  • Pyloric glands — in the antrum, the distal 20%. They secrete mainly mucus, plus the hormone gastrin.
• The four cells of an oxyntic gland:
  • Mucous neck cells — mucus
  • Peptic (chief) cells — large quantities of pepsinogen
  • Parietal (oxyntic) cells — hydrochloric acid AND intrinsic factor
  • Enterochromaffin-like (ECL) cells — histamine
• Surface mucous cells coat the whole mucosa between glands with viscid mucus often more than 1 millimeter thick — a major shell of protection for the stomach wall.
• The alkaline half of the barrier: "at the same time that H⁺ is secreted, HCO₃⁻ diffuses into the blood, so gastric venous blood has a higher pH than arterial blood when the stomach is secreting acid." This is the alkaline tide.

• The numbers that make the point: stimulated parietal cells secrete about 160 mmol/L HCl at a pH of about 0.8. At that pH the H⁺ concentration is about 3 million times that of arterial blood, and concentrating it costs more than 1500 calories of energy per liter of gastric juice. Acid secretion is one of the most energetically expensive things the body does — which is why parietal cells are packed with mitochondria and why the process is so tightly regulated.
• The driving force is the H⁺-K⁺ ATPase — explicitly as the main driving force for hydrochloric acid secretion. The steps:
  • Water inside the parietal cell dissociates into H⁺ and OH⁻.
  • H⁺ is actively secreted into the canaliculus in exchange for K⁺, catalyzed by H⁺-K⁺ ATPase.
  • K⁺ delivered by the basolateral Na⁺-K⁺ ATPase leaks into the lumen and is recycled back by the H⁺-K⁺ ATPase.
  • The basolateral Na⁺-K⁺ ATPase keeps intracellular Na⁺ low, driving Na⁺ reabsorption from the canaliculus — so most K⁺ and Na⁺ in the canaliculus is reabsorbed and H⁺ takes their place.
• Every acid-suppressing drug you will prescribe maps onto this diagram. Proton pump inhibitors irreversibly inhibit the H⁺-K⁺ ATPase — the last common step, which is why they are the most effective. H₂ blockers act one step earlier, on the histamine receptor. Antacids act after the fact, in the lumen. That ordering is exactly why PPIs as more effective than H₂ blockers for severe disease.

• Phase 1 · CEPHALIC — occurs "even before food enters the stomach," from the sight, smell, thought or taste of food; the greater the appetite, the more intense the stimulation. Signals originate in the cerebral cortex and the appetite centers of the amygdala and hypothalamus, travel through the dorsal motor nuclei of the vagi, and account for about 30% of the acid secreted with a meal.
• Phase 2 · GASTRIC — food in the stomach excites long vagovagal reflexes, local enteric reflexes, and the gastrin mechanism. The stimuli are distension and peptides/amino acids in the lumen — and note that gastrin responds to protein, not to acid.
• Phase 3 · INTESTINAL — a small stimulatory component, but mostly INHIBITORY once chyme reaches the small bowel.
• The brakes secretin — especially important for control of pancreatic secretion but it opposes stomach secretion; plus glucose-dependent insulinotropic peptide (GIP), VIP and somatostatin, all with "slight to moderate" inhibitory effects.
• Why the brakes exist, in the words: "to slow passage of chyme from the stomach when the small intestine is already filled or already overactive" — and the enterogastric inhibitory reflexes reduce stomach motility at the same time as secretion.
• Between meals: the stomach secretes only a few milliliters per hour during the interdigestive period — almost entirely of the nonoxyntic type, composed mainly of mucus but little pepsin and almost no acid. Notably, "emotional stimuli may increase interdigestive gastric secretion," which to peptic ulcer development.
• Acid and pepsinogen travel together: in stomachs that have lost the ability to secrete normal amounts of acid, secretion of pepsinogen is also decreased, even though the peptic cells may otherwise appear normal.

• Storage first. Receptive relaxation (GI 1) lets the stomach accept a meal without a rise in pressure.
• The "pyloric pump." Most of the time gastric contractions are weak and only mix. But for about 20% of the time that food is in the stomach they become intense — strong peristaltic, very tight ringlike constrictions beginning in mid-stomach and spreading caudad, generating 50–70 cm H₂O of pressure, about six times as powerful as the mixing waves.
• As the stomach empties, these constrictions "begin farther and farther up the body of the stomach, gradually pinching off the food in the body and adding it to the chyme in the antrum."
• Segmentation in the small intestine is mixing, not propulsion, and its frequency is set by the slow waves from GI 1 — up to 12/min in duodenum and proximal jejunum, 8–9/min in the terminal ileum. The proof that it still needs neural background: "segmentation contractions become exceedingly weak when the excitatory activity of the enteric nervous system is blocked by atropine."
• Propulsion is slow, and this is a real number to hold: peristaltic waves rarely travel more than 10 cm, so net movement along the small intestine averages only 1 cm/min, meaning 3 to 5 hours from pylorus to ileocecal valve.
• Hormones that speed the small bowel: gastrin, CCK, insulin, motilin, serotonin. Hormones that slow it: secretin and glucagon.
• The gastroenteric reflex — distension of the stomach increases peristalsis in the small intestine, conducted through the myenteric plexus.

• Read the table as a defense problem. 1.5 L of pH-1 acid is dumped into a duodenum lined with cells that have no acid resistance. Three things save it: Brunner's glands (the most alkaline secretion in the body, and they sit in exactly the first few centimeters of duodenum), pancreatic bicarbonate, and bile. When that defense fails you get a duodenal ulcer. It also explains why 6.7 liters are secreted and almost all reabsorbed — and why a high-output fistula or severe diarrhea causes such rapid volume loss.

• Three levels of folding multiply the area nearly 1000-fold:
  • Valvulae conniventes (folds of Kerckring) — circular folds, ×3, "especially well developed in the duodenum and jejunum," protruding up to 8 mm into the lumen.
  • Villi — millions, projecting about 1 mm, all the way down to the ileocecal valve.
  • Microvilli (brush border) — on each enterocyte.
• Contrast with the stomach, which absorbs almost nothing — because it "lacks the typical villus type of absorptive membrane" and "the junctions between the epithelial cells are tight junctions." Only a few highly lipid-soluble substances — alcohol and some drugs such as aspirin — are absorbed there, and only in small quantities.
• The daily load, and the reserve: normal absorption is several hundred grams of carbohydrate, 100+ g of fat, 50–100 g of amino acids, 50–100 g of ions and 7–8 liters of water — but capacity is several kilograms of carbohydrate, 500 g of fat, 500–700 g of protein and 20+ liters of water. That enormous reserve is why malabsorption only becomes clinically obvious when a lot of small bowel is lost or diseased.
• Water moves only by osmosis, in either direction. When a hyperosmotic load leaves the stomach, water is pulled from plasma into the duodenal lumen within minutes to make the chyme isosmotic. That is the exact mechanism of dumping syndrome.

• Everything is absorbed as MONOSACCHARIDES — only a small fraction is absorbed as disaccharides.
• The split: glucose accounts for more than 80% of absorbed carbohydrate calories, because it is the final product of starch. The remaining 20% is almost entirely galactose (from milk) and fructose (from cane sugar).
• The luminal-to-blood route, by carrier — this is your "specific transporters" objective:
  • Glucose and galactose in: SGLT1, on the brush border. Secondary active transport — sodium binds SGLT1, which will not transport sodium to the cell interior until SGLT1 also combines with glucose, and then both move together.
  • Fructose in: GLUT5, on the brush border — facilitated diffusion, sodium-independent.
  • All three out: GLUT2, on the basolateral membrane, by facilitated diffusion into the paracellular space and blood.
• The energy source is the basolateral Na⁺-K⁺ ATPase, which depletes intracellular sodium. "the low concentration of sodium inside the cell literally 'drags' sodium to the interior of the cell, and glucose is dragged along with it." Without sodium transport, virtually no glucose can be absorbed.

• The cascade, in the figure: Proteins —(pepsin, stomach)→ proteoses, peptones, polypeptides —(trypsin, chymotrypsin, carboxypolypeptidase, elastase, pancreatic)→ polypeptides + amino acids —(peptidases, brush border)→ amino acids.
• Division of labor: "Trypsin and chymotrypsin split whole and partially digested proteins into peptides of various sizes but do NOT cause release of individual amino acids. However, carboxypolypeptidase splits some peptides into individual amino acids." Trypsin is by far the most abundant.
• Absorption is again sodium co-transport — sodium–amino acid co-transporters on the brush border alongside SGLT1 and the sodium–hydrogen exchanger, all providing secondary active absorption of glucose and amino acids, powered by the basolateral Na⁺-K⁺ ATPase.
• Di- and tripeptides are absorbed too, by PepT1, a H⁺-coupled carrier — and they are absorbed faster than free amino acids, which is why protein hydrolysates outperform amino acid mixtures clinically. Verify this one against lecture; the account stops at peptidases.

• The problem: lipases are water-soluble and can attack the fat globules only on their SURFACES. Everything about fat digestion follows from that one sentence.
• 1 · EMULSIFICATION. Agitation in the stomach begins it; most occurs in the duodenum under bile acids and lecithin. Reducing average particle diameter to under 1 micrometer is "an increase of as much as 1000-fold in total surface area." A small amount of triglyceride is digested in the stomach by lingual lipase — but less than 10% and generally unimportant.
• 2 · HYDROLYSIS. Pancreatic lipase is present in enormous quantities… enough to digest within 1 minute all triglycerides that it can reach. End products: free fatty acids and 2-monoglycerides. Enterocytes contain enteric lipase too, but it is usually not needed.
• 3 · MICELLE FORMATION — and this is the step people underrate. Hydrolysis is "highly reversible, so accumulating products quickly blocks further digestion." Bile salts remove them almost as fast as they form. Micelles are 3–6 nm spherical or cylindrical globules of 20–40 bile salt molecules, each with "a sterol nucleus that is highly fat-soluble and a polar group that is highly water-soluble." Without micelles, only 40% to 50% can be absorbed.
• 4 · RE-ESTERIFICATION AND EXPORT. Inside the enterocyte, fatty acids and monoglycerides are taken up by the smooth endoplasmic reticulum, re-formed into triglycerides, packaged as chylomicrons, released through the cell base, and flow "upward through the thoracic lymph duct" into the blood.
• The exception worth knowing: short- and medium-chain fatty acids (e.g. From butterfat) go directly into the portal blood, because they are "more water soluble and mostly are not reconverted into triglycerides," so they diffuse straight into villus capillaries. Hence MCT oil in fat malabsorption — it needs neither micelles nor lymphatics.

• The colonic bacteria also make vitamin B₁₂, thiamine and riboflavin, plus the gases of flatus — CO₂, hydrogen and methane.
• Feces are about three-quarters water; the solid quarter is roughly 30% dead bacteria, 10–20% fat, 10–20% inorganic matter, 2–3% protein and 30% undigested roughage. The brown color is stercobilin and urobilin, derivatives of bilirubin.

• Acute gastritis is "usually injury of the protective mucosal barrier by drugs, chemicals, or Helicobacter pylori." NSAIDs — aspirin, ibuprofen, naproxen, indomethacin — cause it "perhaps because they inhibit prostaglandins, which normally stimulate the secretion of mucus." Healing usually occurs spontaneously within a few days.
• Chronic gastritis, two types: type A (fundal) — the autoimmune, pernicious-anemia type described above, the most rare and severe, with antibodies to parietal cells, intrinsic factor and gastric cells, associated with diabetes, Addison disease and thyroid disease, and a risk factor for gastric carcinoma. Chronic antral gastritis is "approximately four times more frequent."
• Peptic ulcer definition: "a break, or ulceration, in the protective mucosal lining of the lower esophagus, stomach, or duodenum," exposing submucosa to gastric secretions and autodigestion. Erosions do not penetrate the muscularis mucosae; true ulcers extend through it and damage vessels (hemorrhage) or perforate.
• The two-cause framework: ulcer results from either (1) excess acid–pepsin secretion or (2) diminished ability of the gastroduodenal mucosal barrier to protect against it. H. Pylori does both: it burrows through the barrier and "releases ammonium that liquefies the barrier and stimulates secretion of hydrochloric acid." At least 75% of people with peptic ulcers have chronic H. Pylori infection.
• Risk factors smoking, H. Pylori, habitual NSAID or alcohol use; also emphysema, rheumatoid arthritis and cirrhosis.

• Duodenal ulcer pathophysiology is acid excess — increased parietal cell mass, increased acid and pepsinogen. Gastric ulcer pathophysiology is BARRIER FAILURE: "the primary defect is an abnormality that increases the mucosal barrier's permeability to hydrogen ions. Gastric secretion may be normal or less than normal." Contributors include decreased prostaglandin synthesis reducing mucus, duodenal reflux of bile from a lax pyloric sphincter, and ulcerogenic drugs.
• Dumping syndrome — "rapid emptying of hypertonic chyme from the surgically created residual stomach into the small intestine 10 to 20 minutes after eating," in 5–10% after partial gastrectomy or pyloroplasty. Mechanism: rapid emptying creates a high osmotic gradient → sudden shift of fluid from the vascular compartment into the lumen → plasma volume falls → tachycardia, hypotension, weakness, pallor, sweating, dizziness. It is the same osmotic physics for hyperosmotic chyme, made pathological by removing the pylorus.
• Maldigestion vs malabsorption — the line: maldigestion is deficiency of enzymes (pancreatic lipase, intestinal lactase) or inadequate bile salts; malabsorption is "the result of mucosal disruption caused by gastric or intestinal resection, vascular disorders, or intestinal disease."
• Lactase deficiency — "deficiency of disaccharidase at the brush border… a congenital defect in which a single enzyme, usually lactase, is lacking. Undigested lactose stays in the lumen and pulls water in: it is the most common cause of osmotic diarrhea."
• The four consequences of malabsorption, which double as a checklist of what the small bowel does: (1) severe nutritional deficiency with wasting; (2) OSTEOMALACIA from lack of calcium; (3) inadequate blood coagulation from lack of vitamin K; (4) macrocytic anemia of the pernicious anemia type from diminished B₁₂ and folate absorption.

• The frame: classify by TONICITY relative to 0.9% saline, then ask whether it is a gain or a loss. That gives six boxes and covers every fluid disorder you will be asked about.

• The subtlety worth extracting — makes it explicitly: within hypertonic disorders, sodium gain gives hypervolemia but water loss gives hypoVOLEMIA. Same tonicity, opposite volume status. Same thing again in the hypotonic row. Tonicity and volume are independent axes, and a stem that gives you a sodium and a volume status is testing exactly.
• Signs of isotonic volume DEPLETION: weight loss, dry skin and mucous membranes, decreased urine output, and hypovolemia — rapid heart rate, FLAT neck veins, normal or decreased blood pressure; severe states give hypovolemic shock.
• Signs of isotonic volume EXCESS: weight gain, decreased hematocrit and plasma protein concentration from dilution, distended neck veins, raised blood pressure, and edema from increased capillary hydrostatic pressure. The falling hematocrit is the giveaway — it distinguishes dilution from true anemia when nothing has bled.
• "Dehydration" is a word to use carefully — properly describes a water deficit, but is commonly used for combined sodium and water loss (isotonic dehydration). Pure water deficits are rare because most people have access to water; they occur in the comatose or paralyzed, in fever-driven hyperventilation, and most often from increased renal clearance of free water — impaired tubular function or the inability to concentrate urine, as in diabetes insipidus.

• The thresholds: hypernatremia when serum sodium exceeds 147 mEq/L; hyponatremia when it falls below 135 mEq/L.
• Hyponatremia mechanism: "sodium deficits usually cause hypo-osmolality with movement of water into cells." The symptoms are therefore neurological, because the skull will not expand — confusion, lethargy, seizures, coma.
• Hypernatremia mechanism: ECF hypertonicity pulls water out of cells, giving intracellular dehydration — again mostly neurological, plus thirst if the patient can perceive it.
• The correction rules, which are the clinically dangerous part:
  • Correct chronic hyponatremia SLOWLY — no faster than about 8 mEq/L in 24 hours. Too fast risks osmotic demyelination, because brain cells that have adapted by exporting osmoles cannot re-accumulate them quickly.
  • Correct chronic hypernatremia SLOWLY too — the brain has generated idiogenic osmoles, so rapid water replacement causes cerebral edema.
  • The exception is acute, symptomatic hyponatremia with seizures — that is treated urgently with hypertonic saline, because the risk of the disorder now exceeds the risk of the correction.

• The renal arithmetic, from the figure: 756 mEq/day filtered (180 L × 4.2 mEq/L); 65% reabsorbed in the proximal tubule, 27% in the loop, so only about 8% reaches the distal tubule. Then secretion by the principal cells of the late distal and cortical collecting tubules adds most of what is excreted, and intercalated cells reabsorb some back. Net excretion ≈ 12% of the filtered load, about 92 mEq/day, with 8 mEq lost in feces.
• The regulated step is SECRETION, not filtration. "The most important sites for regulating potassium excretion are the principal cells of the late distal tubules and cortical collecting tubules." The channels have names worth knowing: ENaC (sodium in), ROMK and BK (potassium out).
• Aldosterone drives potassium secretion two ways: it stimulates the Na⁺-K⁺ ATPase (sodium out of the cell, potassium in), and it increases the number of luminal potassium channels, raising permeability. Read that backwards and hyperkalemia in Addison disease, in ACE inhibitor use, and with potassium-sparing diuretics all fall out of one mechanism.
• And potassium closes the loop itself: increased potassium concentration stimulates aldosterone secretion by the adrenal cortex, which further stimulates potassium secretion. This is the direct feedback architecture from Endo 1 and Endo 4 — the glomerulosa answers to potassium and angiotensin II, not to ACTH.
• ACUTE acidosis DECREASES potassium secretion — the mechanism is that high H⁺ reduces Na⁺-K⁺ ATPase activity, lowering intracellular potassium and therefore luminal diffusion; it may also reduce the number of luminal potassium channels. But CHRONIC acidosis over several days INCREASES urinary potassium excretion. So acute acidosis raises serum potassium while chronic acidosis depletes total body potassium — which is exactly the DKA trap below.

• What the treatment list leaves out, and it matters: insulin, bicarbonate and resins either shift potassium or remove it, and none of them protects the heart in the meantime. IV calcium (gluconate or chloride) does not change the serum potassium at all — it stabilizes the myocardial membrane and is given first when the ECG is abnormal. Then shift, then remove.
• Note the reciprocal trap after a crush injury or burn, potassium floods out of damaged cells; if renal function holds, it is excreted — and then "as cell repair begins, HYPOkalemia develops without adequate intake." The same patient swings both ways within days.

• Total body calcium ≈ 1200 g, and 99% is in bone as hydroxyapatite.
• Of plasma calcium: about 50% is protein-bound (2.5 mEq/L) and about 40% is free/ionized (2.4 mEq/L). Total circulating calcium is 4.5–5.5 mEq/L, or 8.6–10.5 mg/dL.
• Only ionized calcium is physiologically active, which generates two corrections you will be asked to apply: low albumin lowers the TOTAL calcium without lowering the ionized fraction (add roughly 0.8 mg/dL per 1 g/dL the albumin is below 4); and alkalosis increases protein binding, lowering ionized calcium at an unchanged total — the mechanism of perioral tingling and carpopedal spasm during hyperventilation.

• The framing is honest about what it is: "the concentrations of anions and cations in plasma must be equal to maintain electrical neutrality. Therefore, there is no real anion gap in the plasma. However, only certain cations and anions are routinely measured… The anion gap — which is only a diagnostic concept — is the difference between unmeasured anions and unmeasured cations."
• The unmeasured species, named: "the most important unmeasured cations include calcium, magnesium, and potassium, and the major unmeasured anions are albumin, phosphate, sulfate, and other organic anions." The gap "will increase if unmeasured anions rise or if unmeasured cations fall."
• The worked example: 144 − 24 − 108 = 12 mEq/L, with a normal range of 8 to 16 mEq/L.

• The four general causes of metabolic acidosis: (1) failure of the kidneys to excrete metabolic acids; (2) formation of excess metabolic acids; (3) addition of acids by ingestion or infusion; (4) LOSS OF BASE from the body fluids, which has the same effect as adding an acid.
• The split is the one your objective asks for: "In metabolic acidosis a NORMAL anion gap is characteristic of conditions related to bicarbonate loss with retention of chloride to maintain an ionic balance. This is called hyperchloremic metabolic acidosis. An elevated anion gap" indicates increased noncarbonic acids.

• The specific entities, with the mechanism attached:
  • Diarrhea is probably the MOST FREQUENT cause of metabolic acidosis. Mechanism: loss of large amounts of sodium bicarbonate into the feces — the same effect as losing large amounts of bicarbonate in the urine. "can be serious and can cause death, especially in young children."
  • Vomiting cuts both ways, and this is a favorite question. "Vomiting of gastric contents alone would cause a loss of acid and a tendency toward ALKALOSIS… However, vomiting large amounts from deeper in the gastrointestinal tract causes loss of bicarbonate and results in metabolic ACIDOSIS."
  • Renal tubular acidosis — a defect in renal secretion of H⁺, reabsorption of HCO₃⁻, or both, of two types: impaired tubular HCO₃⁻ reabsorption (bicarbonate lost in urine) or inability of the H⁺ secretory mechanism to establish normal acidic urine (alkaline urine despite systemic acidosis). Causes include chronic renal failure, insufficient aldosterone (Addison disease), and Fanconi syndrome.
  • Diabetes mellitus: without insulin, "some of the fats are split into acetoacetic acid," metabolized for energy in place of glucose; blood levels rise very high, causing severe metabolic acidosis.

• Definition and causes: bicarbonate is increased, "usually caused by excessive loss of metabolic acids." the list: prolonged vomiting, gastrointestinal suctioning, excessive bicarbonate intake, hyperaldosteronism, and diuretic therapy. ingestion of alkaline drugs such as sodium bicarbonate for gastritis or peptic ulcer.
• Why vomiting-induced alkalosis will not self-correct — this is the mechanism to be able to recite. In hypochloremic metabolic alkalosis, "renal compensation is not very effective because the volume depletion and loss of electrolytes (Na⁺, K⁺, H⁺, Cl⁻) stimulate a PARADOXIC response by the kidneys. The kidneys increase sodium and bicarbonate reabsorption with excretion of hydrogen. Bicarbonate is reabsorbed because the ECF chloride concentration is decreased. When the potassium concentration is depleted, hydrogen moves to the intracellular space and is excreted to maintain electrochemical balance. The urine is ACIDIC, and the reabsorbed bicarbonate prevents correction of the alkalosis."
• Hence the treatment, which follows exactly from: "Correction is achieved when the ECF is expanded with a solution of sodium chloride and potassium. The volume replacement decreases the renal stimulus to reabsorb Na⁺, and chloride as an anion is replaced. Bicarbonate then can be" excreted. This is why it is called saline-responsive alkalosis — and why hyperaldosteronism, which is saline-RESISTANT, needs the aldosterone blocked instead.

Your fifth objective names five categories explicitly — renal, pulmonary, gastrointestinal, metabolic and toxicologic. Here they are, sorted that way.

• Salicylate poisoning belongs in two boxes at once, and that is exactly why it is a favorite vignette: it stimulates the respiratory center directly (respiratory alkalosis) and is itself an acid that uncouples oxidative phosphorylation (raised-gap metabolic acidosis). The classic adult picture is a mixed disorder with a near-normal pH — which is the situation Ren 1's rule was built for: if HCO₃⁻ and PCO₂ are moving in opposite directions, it is two primary disorders.
• Treatment, in principle: "The best treatment for acidosis or alkalosis is to CORRECT THE CONDITION THAT CAUSED the abnormality." Where that is not possible: for acidosis, sodium bicarbonate orally, or IV — though "because of the potentially dangerous physiological effects of such treatment, other substances are often used instead, such as sodium lactate and sodium gluconate," whose anions are metabolized leaving sodium bicarbonate behind. For alkalosis, ammonium chloride by mouth: the ammonia is converted by the liver to urea, "this reaction liberates HCl."

• The five headline functions, worth learning as the spine of this lecture: (1) filtration and storage of blood; (2) metabolism of carbohydrates, proteins, fats, hormones and foreign chemicals; (3) formation of bile; (4) storage of vitamins and iron; (5) formation of coagulation factors.
• Size: the largest organ, about 2% of body weight — roughly 1.5 kg in an adult.
• The functional unit is the LIVER LOBULE — a cylinder several millimeters long and 0.8–2 mm across; the human liver contains 50,000 to 100,000 of them.
• How the lobule is built: around a central vein draining to the hepatic veins and vena cava. Hepatic plates — usually two cells thick — radiate from the central vein "like spokes in a wheel." Between adjacent cells run bile canaliculi, which drain outward to bile ducts in the fibrous septa.
• Blood runs the other way. Portal venules in the septa receive blood mainly from the venous outflow of the gastrointestinal tract, which then flows through hepatic sinusoids between the plates and inward to the central vein. "Thus, the hepatic cells are exposed continuously to portal venous blood." Hepatic arterioles are also in the septa and many empty directly into the sinusoids.
• The sinusoids are lined by two cell types: ordinary endothelial cells and large Kupffer cells (reticuloendothelial macrophages).
• The liver is a blood RESERVOIR. Normal hepatic blood volume is about 450 mL — almost 10% of total blood volume. When right atrial pressure rises, the liver expands and can hold 0.5 to 1 liter extra, especially in cases of cardiac failure with peripheral congestion.
• And it makes half the body's lymph. Sinusoidal pores are so permeable that fluid and protein pass into the spaces of Disse; hepatic lymph has a protein concentration of about 6 g/dL, only slightly less than plasma, and "about half of all the lymph formed in the body under resting conditions arises in the liver."

• The blood-cleansing job, with a number that makes it real: portal blood cultured before the liver almost always grows colon bacilli, while systemic blood almost never does. Kupffer cells engulf a bacterium in less than 0.01 second on contact, and "probably less than 1% of the bacteria entering the portal blood from the intestines succeeds in passing through the liver."
• Carbohydrate — the "GLUCOSE BUFFER" function. Glycogen storage lets the liver remove excess glucose after a meal and return it when blood glucose falls. The evidence that it matters: "in a person with poor liver function, blood glucose after a carbohydrate-rich meal may rise two to three times as much as normal." Add conversion of galactose and fructose to glucose and gluconeogenesis, which occurs to a significant extent only when glucose falls below normal.
• Protein — four jobs, and the second one kills you if it fails: (1) deamination of amino acids; (2) formation of UREA to remove ammonia; (3) formation of plasma proteins; (4) interconversion of amino acids. "If the liver does not form urea, the plasma ammonia concentration rises rapidly and results in hepatic coma and death. Indeed, even greatly decreased blood flow through the liver" can do it. That last clause is the whole mechanism of encephalopathy from a portosystemic shunt — the hepatocytes may be alive but the blood is not reaching them.
• Fat: oxidation of fatty acids for energy, and synthesis of large quantities of cholesterol, phospholipids and most lipoproteins.
• Coagulation: the liver makes fibrinogen, prothrombin, and factors VII, IX and X — and "in the absence of vitamin K, the concentrations of all these substances decrease markedly and almost prevent blood coagulation." So a prolonged PT/INR in liver disease has two possible causes — synthetic failure or vitamin K deficiency from cholestasis — and giving vitamin K distinguishes them.
• Detoxification and excretion: the liver detoxifies or excretes into bile sulfonamides, penicillin, ampicillin, erythromycin; it chemically alters or excretes thyroxine and essentially all the steroid hormones — estrogen, cortisol, aldosterone. "Liver damage can lead to excess accumulation of one or more of these hormones… and therefore cause overactivity of the hormonal systems." That single sentence explains the gynecomastia, spider nevi, palmar erythema and testicular atrophy of cirrhosis — unmetabolized estrogen — and the secondary hyperaldosteronism that drives ascites.
• Storage — with real durations: vitamin A is stored in the greatest quantity, enough to prevent deficiency for 10 months; vitamin D for 3–4 months; vitamin B₁₂ for at least a year and perhaps several. Iron is stored as ferritin, formed when iron combines reversibly with apoferritin.