The pituitary gland sits in the sella turcica, a saddle-shaped depression in the sphenoid bone.

The diaphragma sellae is a dural fold forming the roof of the sella turcica with a central opening for the pituitary stalk.

The anterior pituitary (adenohypophysis) develops from Rathke’s pouch, an ectodermal outgrowth from the oral cavity roof.

The posterior pituitary (neurohypophysis) develops from neuroectoderm as a downgrowth from the diencephalon (infundibulum).

Craniopharyngioma is a benign tumor arising from remnants of Rathke’s pouch along the craniopharyngeal canal.

The pituitary gland receives blood from superior and inferior hypophyseal arteries, which are branches of the internal carotid artery.

The pituitary stalk (infundibulum) passes through the central aperture of the diaphragma sellae connecting hypothalamus to pituitary.

A pituitary tumor expanding superiorly compresses the optic chiasm, affecting crossing nasal retinal fibers causing bitemporal hemianopia (loss of peripheral vision bilaterally).

Chromophobes have poorly staining cytoplasm with few or no granules and may represent degranulated or stem cells.

Somatotrophs are acidophilic cells secreting growth hormone (GH) and constitute about 50% of anterior pituitary cells.

Lactotrophs (mammotrophs) are acidophilic cells that secrete prolactin.

Herring bodies are dilated axon terminals in the pars nervosa (posterior pituitary) containing oxytocin and ADH neurosecretory granules.

Pituicytes are glial-like supporting cells in the neurohypophysis (posterior pituitary) that support unmyelinated axons from hypothalamus.

Corticotrophs are basophilic cells that secrete ACTH (adrenocorticotropic hormone), which stimulates the adrenal cortex.

The adrenal glands sit on the superior poles of the kidneys at approximately the T12 vertebral level.

Zona glomerulosa, the outermost cortical layer, produces mineralocorticoids (aldosterone).

The adrenal medulla develops from neural crest cells (chromaffin cells) that migrate into the developing gland.

The right adrenal vein is short and drains directly into the IVC due to proximity.

Adrenal glands have a rich blood supply from three sources: superior suprarenal from inferior phrenic, middle suprarenal from aorta, and inferior suprarenal from renal arteries.

Chromaffin cells are modified postganglionic sympathetic neurons in the adrenal medulla that secrete catecholamines directly into blood.

The adrenal cortex develops from intermediate mesoderm (specifically, coelomic epithelium near the urogenital ridge).

The fetal zone is a large, transient zone producing DHEA for placental estrogen synthesis.

21-hydroxylase deficiency accounts for >90% of congenital adrenal hyperplasia cases, causing cortisol deficiency, aldosterone deficiency, and androgen excess leading to virilization.

Neural crest cells migrate into the adrenal cortex around the 7th week of gestation to form chromaffin cells of the medulla.

The thyroid develops from an endodermal diverticulum at the foramen cecum (junction of anterior 2/3 and posterior 1/3 of tongue) and descends via the thyroglossal duct.

The thyroid gland lies anterior to the 2nd to 4th tracheal rings (C5-T1 vertebral level).

The thyroid receives blood from superior thyroid artery (from external carotid) and inferior thyroid artery (from thyrocervical trunk).

The recurrent laryngeal nerve crosses the inferior thyroid artery (anterior or posterior) near the thyroid gland.

Follicular cells (thyrocytes) line the thyroid follicles and synthesize T3 (triiodothyronine) and T4 (thyroxine) stored as colloid.

The pituitary gland sits in the sella turcica of the sphenoid bone.

Rathke’s pouch is an ectodermal outpouching from the roof of the stomodeum that forms the adenohypophysis.

Somatotrophs are acidophilic cells that secrete growth hormone (somatotropin).

The hypophyseal portal system carries releasing hormones from the hypothalamus to the anterior pituitary.

The optic chiasma lies directly above the pituitary gland.

Acidophils have affinity for acidic dyes like eosin, appearing pink/red.

The posterior pituitary (neurohypophysis) stores and releases oxytocin and ADH, which are synthesized in hypothalamic nuclei (paraventricular and supraoptic).

Herring bodies are dilated axon terminals in the pars nervosa (posterior pituitary) containing neurosecretory granules of ADH and oxytocin.

Chromophobes are cells with little cytoplasm and no significant granules–they do not actively secrete hormones.

The infundibulum (pituitary stalk) connects the pituitary gland to the hypothalamus.

The adrenal medulla develops from neural crest cells (neuroectoderm), which also form sympathetic ganglia.

Zona glomerulosa is the outermost cortical layer and produces mineralocorticoids (aldosterone).

The adrenal gland receives blood from three sources: superior suprarenal artery (from inferior phrenic), middle suprarenal artery (from aorta), and inferior suprarenal artery (from renal artery).

The right adrenal vein is short and drains directly into the IVC.

Zona fasciculata, the middle and largest cortical layer, produces glucocorticoids, primarily cortisol.

Chromaffin cells are modified postganglionic sympathetic neurons in the adrenal medulla.

There is no distinct anatomical boundary between the adrenal cortex and medulla.

The fetal adrenal cortex has a large inner fetal zone (80%) that produces DHEA for placental estrogen synthesis.

The adrenal glands are enclosed within the renal fascia (Gerota’s fascia) along with the kidneys and perirenal fat.

The thyroid develops from an endodermal thickening at the foramen cecum (junction of anterior 2/3 and posterior 1/3 of tongue).

The thyroid follicle is the structural and functional unit, consisting of a single layer of follicular cells surrounding colloid (stored thyroglobulin).

Parafollicular cells (C cells) are derived from neural crest and secrete calcitonin, which lowers blood calcium.

The recurrent laryngeal nerve crosses near the inferior thyroid artery (variably anterior or posterior).

Colloid is composed primarily of thyroglobulin, a glycoprotein containing tyrosine residues that are iodinated to form T3 and T4.

The thyroid gland is enclosed in pretracheal fascia, which attaches to the larynx and trachea.

The thyroid isthmus typically overlies tracheal rings 2-4, just below the cricoid cartilage.

Berry’s ligament (ligament of Berry) is a posterior suspensory ligament attaching the thyroid to the cricoid cartilage and trachea.

Thyroglossal cysts occur along the thyroglossal duct path, most commonly in the infrahyoid midline region.

Superior parathyroids develop from the 4th pharyngeal pouch (with ultimobranchial body).

Typically four parathyroid glands exist–two superior and two inferior–located on the posterior surface of the thyroid gland.

The inferior thyroid artery supplies both superior and inferior parathyroid glands.

Chief cells (principal cells) are the main PTH-secreting cells.

Parathyroid glands are typically located on the posterior surface of thyroid lobes, within the thyroid capsule but outside the thyroid tissue.

Oxyphil cells contain numerous mitochondria, giving them an eosinophilic appearance.

Inferior parathyroids develop from the 3rd pharyngeal pouch with the thymus and descend together.

Parathyroid glands lie within the thyroid capsule (true capsule of the thyroid) but outside the thyroid parenchyma.

Islets of Langerhans are most concentrated in the tail of the pancreas.

Beta cells constitute 60-70% of islet cells and secrete insulin.

The exocrine pancreas is a compound acinar (serous) gland producing digestive enzymes.

Centroacinar cells are pale-staining cells extending into the center of acini–they are the beginning of the intercalated duct system.

The pancreas develops from dorsal and ventral pancreatic buds of the foregut endoderm.

The main pancreatic duct joins the common bile duct to form the hepatopancreatic ampulla, opening at the major duodenal papilla (of Vater).

Alpha cells (15-20% of islet cells) secrete glucagon, which raises blood glucose.

The pancreatic head receives blood from superior pancreaticoduodenal artery (from gastroduodenal) and inferior pancreaticoduodenal artery (from SMA).

Zymogen granules contain inactive enzyme precursors (trypsinogen, chymotrypsinogen, procarboxypeptidase, etc.) that are activated in the duodenum.

The tail of the pancreas extends to the splenic hilum within the splenorenal ligament.

The kidneys extend from T12 to L3 vertebral levels.

The nephron is the structural and functional unit, comprising the renal corpuscle (glomerulus + Bowman’s capsule) and renal tubule.

Renal arteries arise from the abdominal aorta at L1-L2 level, just below the SMA.

The left renal vein receives the left gonadal vein, left suprarenal vein, and sometimes the left inferior phrenic vein.

Perirenal fat (adipose capsule) lies between the renal capsule and renal fascia.

Juxtaglomerular cells are modified smooth muscle cells in afferent arterioles that secrete renin in response to decreased blood pressure.

The macula densa is a specialized region of the distal convoluted tubule adjacent to the afferent arteriole.

Podocytes are specialized epithelial cells forming the visceral layer of Bowman’s capsule.

The renal pelvis is the funnel-shaped expansion that collects urine from major calyces and continues as the ureter at the ureteropelvic junction.

The permanent kidney (metanephros) develops from intermediate mesoderm (metanephric blastema and ureteric bud).

In horseshoe kidney, the inferior poles are fused across the midline by an isthmus, typically at L3-L4 level.

Unilateral renal agenesis is more common in males (ratio 1.8:1).

Autosomal dominant polycystic kidney disease (ADPKD) is commonly associated with hepatic cysts (40-60% of patients).

Pelvic kidney occurs when the developing kidney fails to ascend from its origin in the pelvis to its normal lumbar position.

Duplicated ureter (duplex collecting system) results from early bifurcation of the ureteric bud.

Potter sequence (oligohydramnios sequence) results from bilateral renal agenesis causing absent fetal urine, leading to oligohydramnios.

The bladder develops from the upper part of the urogenital sinus (derived from the cloaca).

The trigone is a smooth triangular area on the posterior wall (base) of the bladder, bounded by the two ureteric orifices and the internal urethral orifice.

The bladder is supplied by superior vesical artery (from patent part of umbilical artery) and inferior vesical artery (from internal iliac).

The detrusor muscle (smooth muscle) is innervated by parasympathetic nerves from pelvic splanchnic nerves (S2-S4), which cause contraction during micturition.

The internal urethral sphincter is composed of smooth muscle fibers from the detrusor at the bladder neck, under autonomic control.

Transitional epithelium (urothelium) lines the bladder, ureters, and renal pelvis.

The prostate develops from multiple endodermal outgrowths of the prostatic urethra (part of urogenital sinus) under influence of fetal androgens.

BPH occurs primarily in the transitional zone surrounding the urethra, causing urinary obstruction.

The prostate lies inferior to the bladder neck, surrounding the prostatic urethra.

The prostate receives blood mainly from the inferior vesical artery (branch of internal iliac).

The ejaculatory ducts (formed by union of vas deferens and seminal vesicle duct) traverse the central zone to open into the prostatic urethra at the seminal colliculus.

The male urethra has four parts: pre-prostatic (intramural), prostatic, membranous, and spongy (penile).

The membranous urethra is the narrowest AND least distensible part, passing through the urogenital diaphragm.

The prostatic and membranous urethra are lined by transitional epithelium (continuous with bladder).

The female urethra opens at the external urethral orifice, located in the vestibule between the clitoris and vaginal opening.

An imaginary transverse line between the ischial tuberosities divides the perineum into the anterior urogenital triangle (containing external genitalia) and posterior anal triangle (containing anal canal).

The posterior pituitary (neurohypophysis) stores and releases ADH and oxytocin, which are synthesized in the hypothalamus.

Oxytocin causes contraction of myoepithelial cells in the mammary glands, resulting in milk ejection.

Dopamine is the “Prolactin-Inhibiting Factor” (PIF) released from the hypothalamus to keep prolactin levels in check.

Somatotropes are acidophilic cells that secrete GH.

Thyroid-Stimulating Hormone (TSH) binds to TSH receptors on thyroid follicular cells, stimulating synthesis and secretion of thyroid hormones.

The pineal gland secretes melatonin, which is essential for regulating circadian rhythms and the sleep-wake cycle.

Beta cells of the islets of Langerhans are responsible for synthesizing and secreting insulin in response to high blood glucose.

Diabetes mellitus causes hyperglycemia, leading to osmotic diuresis (excessive urine production or polyuria).

Melanocyte-stimulating hormone (MSH) is produced by the intermediate lobe, which is vestigial in adult humans.

ADH (Vasopressin) acts on V2 receptors in the collecting ducts to increase water permeability via aquaporin-2 channels.

Adrenocorticotropic hormone (ACTH) from the anterior pituitary stimulates the zona fasciculata of the adrenal cortex.

Glucagon stimulates the liver to break down glycogen into glucose (glycogenolysis) to raise blood sugar.

Aldosterone acts on the distal tubules and collecting ducts of the kidney to increase sodium reabsorption and potassium excretion.

Estrogen is responsible for the development of secondary sexual characteristics and maintenance of the reproductive tract in females.

Prolactin is the primary hormone responsible for the synthesis of milk in the mammary glands.

Thyroid hormones increase the basal metabolic rate by stimulating oxygen consumption and heat production in most tissues.

The zona glomerulosa is the outermost layer of the adrenal cortex and is specifically responsible for aldosterone production.

Somatostatin, also known as Growth Hormone Inhibiting Hormone (GHIH), inhibits the release of many hormones, including gastrin and gastric acid.

The nephron is the basic structural and functional unit where filtration, reabsorption, and secretion occur to form urine.

Approximately 65% of filtered sodium and water is reabsorbed in the proximal convoluted tubule via various transport mechanisms.

ADH binds to V2 receptors in the collecting duct, causing the insertion of AQP-2 water channels into the apical membrane.

Angiotensin-Converting Enzyme (ACE) is found in high concentrations in pulmonary capillaries and converts inactive Angiotensin I into the potent vasoconstrictor Angiotensin II.

JG cells are modified smooth muscle cells in the afferent arteriole that synthesize and store renin.

Aldosterone acts on principal cells in the collecting duct to increase sodium reabsorption and potassium secretion.

The macula densa cells monitor NaCl concentration in the distal tubule and signal the JG cells to adjust renin release.

The loop of Henle dips into the renal medulla, creating an osmotic gradient essential for urine concentration.

Glomerular filtration is a passive process driven by the high hydrostatic pressure in glomerular capillaries forcing fluid through the filtration membrane.

In healthy individuals, 100% of filtered glucose is reabsorbed in the proximal tubule by secondary active transport.

ANP is released by the heart in response to atrial stretch, inhibiting sodium reabsorption in the kidney to reduce blood volume.

The thick ascending limb is actively impermeable to water, which allows for the dilution of tubular fluid.

Sodium is the most abundant extracellular cation and the primary determinant of plasma osmolality.

The micturition reflex is an autonomic spinal cord reflex, though it can be inhibited or facilitated by higher brain centers.

The detrusor muscle is the smooth muscle layer of the bladder wall that contracts to expel urine.

The kidneys maintain stable blood flow and GFR despite changes in arterial blood pressure through intrinsic autoregulatory mechanisms like the myogenic response.

While urine pH can range from 4.5 to 8.0, the average normal urine pH is slightly acidic, around 6.0.

Aldosterone promotes potassium secretion into the tubular fluid in exchange for sodium reabsorption.

Creatinine is freely filtered and undergoes a small amount of active secretion in the tubules.

The collecting duct, under the influence of ADH, allows for water reabsorption to concentrate the urine.

Constriction of the afferent arteriole reduces blood flow to the glomerulus, thereby decreasing glomerular hydrostatic pressure and GFR.

The thick ascending limb actively reabsorbs ions but lacks aquaporins, making it impermeable to water.

Erythropoietin is produced by interstitial cells in the peritubular capillary bed of the kidney in response to hypoxia.

The basic micturition reflex is a spinal cord reflex integrated in the sacral segments (S2-S4).

GFR is increased by increasing glomerular hydrostatic pressure, achieved by afferent dilation (more flow in) or efferent constriction (more resistance to flow out).

Para-aminohippuric acid (PAH) is almost completely cleared from the renal plasma in a single pass; thus, PAH clearance approximates renal plasma flow.

The bladder wall is formed by smooth muscle (detrusor), which provides the contractile force for urination.

Parathyroid hormone (PTH) increases plasma calcium and decreases plasma phosphate levels.

GFR is approximately 125 mL/min (180 liters per day) in a healthy young adult.

Atrial Natriuretic Peptide (ANP) inhibits ADH release and promotes sodium and water excretion to reduce blood volume.

Urine is formed by the summation of glomerular filtration, tubular reabsorption, and tubular secretion.

PTH increases the activity of the 1-alpha-hydroxylase enzyme in the kidney, which converts inactive Vitamin D to its active form (calcitriol).

Sympathetic stimulation causes vasoconstriction of the renal arterioles, leading to a decrease in renal blood flow and GFR.

The proximal convoluted tubule is the main site of water reabsorption (isosthenuric reabsorption) due to its high permeability and tight junctions.

In the distal tubule and collecting duct, sodium is reabsorbed and potassium is secreted, a process primarily regulated by aldosterone.

The kidney maintains a constant GFR and renal blood flow despite variations in arterial pressure between 80 and 180 mmHg.

Parasympathetic fibers via pelvic nerves stimulate detrusor muscle contraction to expel urine during micturition.

A surge in Luteinizing Hormone (LH) mid-cycle triggers the rupture of the ovarian follicle and ovulation.

Human Chorionic Gonadotropin (hCG) is secreted by the developing embryo and mimics LH to maintain the corpus luteum for progesterone production.

Leydig cells (interstitial cells) are stimulated by LH to synthesize and secrete testosterone.

Testosterone is essential for the maturation of sperm, and FSH stimulates Sertoli cells to provide nourishment for sperm.

Estrogen promotes the development of female secondary sexual characteristics, such as breast development and fat distribution.

Fertilization usually occurs in the ampulla of the fallopian tube.

Colostrum is a thin, yellowish fluid produced during the first few days postpartum, rich in antibodies and protein.

An LH surge is necessary for ovulation to occur.

Seminiferous tubules are the site where spermatogonia undergo meiosis to become mature sperm.

Sertoli cells provide the nurturing environment and necessary nutrients for developing spermatids.

The proliferative phase (follicular phase) is driven by estrogen and causes rapid regrowth of the endometrium after menstruation.

The average menstrual cycle lasts 28 days, although variations between 21 and 35 days are considered normal.

Progesterone is essential to maintain the decidual lining of the uterus and inhibit uterine contractions during pregnancy.

Epididymis is where sperm acquire motility and are stored until ejaculation.

Seminal vesicles contribute about 60-70% of the semen volume, which is rich in fructose for sperm energy.

Testosterone is the primary androgen responsible for male sexual development and characteristics.

A pre-ovulatory surge of LH, FSH, and Estrogen is necessary for the final maturation of the oocyte and rupture of the follicle.

Menopause is caused by the exhaustion of the ovarian follicular pool, leading to low estrogen levels and cessation of menses.

Progesterone levels rise significantly during the secretory phase (luteal phase) produced by the corpus luteum.

Implantation typically occurs about 6-7 days after fertilization when the blastocyst reaches the endometrium.

Growing ovarian follicles secrete estrogen during the follicular phase of the menstrual cycle.

FSH (Follicle-Stimulating Hormone) initiates the development of ovarian follicles during the follicular phase.

Testosterone acts on Sertoli cells (and peritubular cells) to promote the differentiation and maturation of spermatogenic cells.

Seminal vesicles secrete fructose, which is the primary energy source for ejaculated sperm motility.

Sertoli cells secrete inhibin, which provides negative feedback on FSH secretion.

The luteal phase (post-ovulatory) is relatively constant in length at 14 days, following ovulation on day 14 of a 28-day cycle.

Oxytocin stimulates uterine smooth muscle contraction during labor via a positive feedback loop (Ferguson reflex).

The blood-testis barrier, formed by tight junctions between Sertoli cells, protects developing sperm (which are genetically different) from the immune system.

Progesterone exerts negative feedback on the anterior pituitary to inhibit LH secretion in the luteal phase.

Gonadotropin-Releasing Hormone (GnRH) from the hypothalamus stimulates the anterior pituitary to release both FSH and LH.

Theca interna cells produce androgens under LH stimulation, which are then converted to estrogen by granulosa cells.

The acrosome reaction releases enzymes that digest the zona pellucida of the ovum, allowing the sperm to fuse with the egg membrane.

Sertoli cells secrete inhibin B, which provides selective negative feedback to inhibit FSH secretion from the anterior pituitary.

The hypothalamic-pituitary-gonadal axis (GnRH from hypothalamus triggering FSH/LH from the pituitary) is the central regulatory mechanism for reproductive function in both males and females.

Endocrine signaling involves secretion of hormones into the bloodstream, allowing them to reach distant target organs.

Paracrine signaling involves local diffusion of signaling molecules to affect neighboring cells.

In autocrine signaling, a cell secretes a hormone that binds to receptors on its own surface.

Epinephrine is a first messenger (hormone) that binds to cell surface receptors. cAMP, IP3, and calcium ions are all intracellular second messengers generated after receptor activation.

Adenylyl cyclase converts ATP to cyclic AMP (cAMP).

IP3 binds to receptors on the endoplasmic reticulum, triggering release of stored calcium into the cytoplasm.

Guanylyl cyclase converts GTP to cyclic GMP (cGMP). cAMP is made by adenylyl cyclase.

Pheochromocytoma arises from chromaffin cells of the adrenal medulla.

Pheochromocytoma produces excess catecholamines–epinephrine and norepinephrine–causing hypertension, tachycardia, and sweating.

The classic triad is episodic headache, sweating, and palpitations (tachycardia).

Thyroid hormones (T3 and T4/thyroxine) require iodine for synthesis.

Follicular cells of the thyroid synthesize thyroglobulin, the scaffold for thyroid hormone synthesis.

Thyroid peroxidase (TPO) oxidizes iodide to iodine and attaches it to tyrosine residues on thyroglobulin (organification).

MIT (monoiodotyrosine) + DIT (diiodotyrosine) = T3 (triiodothyronine, 3 iodines).

T3 is 3-5 times more potent than T4 at nuclear receptors.

Beta cells of pancreatic islets of Langerhans produce insulin.

Proinsulin is cleaved by prohormone convertases to produce insulin (A and B chains) and C-peptide.

Elevated blood glucose is the primary stimulus for insulin release from beta cells.

Insulin binds to insulin receptor, a receptor tyrosine kinase.

GLUT4 is insulin-dependent, found in muscle and adipose tissue.

Insulin is anabolic–it promotes glycogenesis (glycogen synthesis), lipogenesis, and protein synthesis.

Hypoglycemia is defined as blood glucose <70 mg/dL.

Hypoglycemia triggers sympathetic response–tremors, sweating, tachycardia, anxiety.

Fasting plasma glucose ≥126 mg/dL on two separate occasions diagnoses diabetes mellitus.

Metabolic syndrome criteria include elevated fasting glucose, low HDL, elevated triglycerides, increased waist circumference, and hypertension.

Central (visceral/abdominal) obesity is more metabolically harmful than peripheral obesity.

BMI classification: <18.5 = underweight, 18.5-24.9 = normal, 25-29.9 = overweight, ≥30 = obese.

Leptin is the “satiety hormone” produced mainly by white adipose tissue.

Leptin binds to receptors in the hypothalamus (arcuate nucleus), suppressing appetite and promoting energy expenditure.

Congenital leptin deficiency causes severe early-onset obesity due to uncontrolled appetite.

Glycolysis is a cytoplasmic pathway converting glucose to pyruvate.

Glycolysis produces 4 ATP but consumes 2 ATP (hexokinase and PFK-1 steps), giving net 2 ATP.

PFK-1 is the committed, rate-limiting step of glycolysis (fructose-6-P → fructose-1,6-bisphosphate).

Aerobic glycolysis ends with pyruvate, which enters mitochondria for TCA cycle.

Lactate dehydrogenase (LDH) converts pyruvate to lactate, regenerating NAD+ for continued glycolysis without oxygen.

TCA cycle enzymes are located in mitochondrial matrix (except succinate dehydrogenase, which is in inner membrane).

One TCA cycle turn produces 3 NADH (at isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, and malate dehydrogenase).

Citrate synthase catalyzes the first reaction of TCA cycle: acetyl-CoA + oxaloacetate → citrate.

Isocitrate dehydrogenase is the rate-limiting step, regulated by ADP (activator) and ATP/NADH (inhibitors). α-ketoglutarate dehydrogenase is also regulated but not the main rate-limiter.

Fumarate is produced in the urea cycle (from argininosuccinate) and enters TCA cycle.

Liver is the primary site of gluconeogenesis (and kidney during prolonged fasting).

PEPCK converts oxaloacetate to phosphoenolpyruvate, bypassing the irreversible pyruvate kinase reaction of glycolysis.

Glucagon (from pancreatic alpha cells) stimulates gluconeogenesis and glycogenolysis during fasting to raise blood glucose.

Fatty acids cannot be converted to glucose in humans (acetyl-CoA cannot form pyruvate).

Normal arterial pH is 7.35-7.45. pH <7.35 is acidemia; pH >7.45 is alkalemia.

Bicarbonate (HCO3⁻/H2CO3) is the major extracellular buffer due to its abundance and connection to respiratory regulation (CO2).

Respiratory acidosis results from CO2 retention (hypoventilation), causing increased H2CO3 and decreased pH.

Metabolic acidosis shows low pH (<7.35) and low bicarbonate (<22 mEq/L) due to acid gain or bicarbonate loss.

Leydig cells (interstitial cells) in testes produce testosterone under LH stimulation.

Prolactin from anterior pituitary stimulates milk production (lactogenesis) in mammary glands.

Prolactinomas arise from lactotrophs, which are acidophils.

Craniopharyngiomas arise from remnants of Rathke’s pouch, which originates from surface ectoderm of the stomodeum (roof of primitive mouth).

The neurohypophysis (posterior pituitary) appears paler because it consists of unmyelinated axons from hypothalamic neurons (supraoptic and paraventricular nuclei) and supporting pituicytes (modified glial cells).

The hypophyseal portal system begins with the superior hypophyseal artery forming a primary capillary plexus in the median eminence where hypothalamic releasing/inhibiting hormones are released.

The adrenal cortex develops from coelomic epithelium (mesothelium) near the developing gonad during weeks 4-5.

Zona glomerulosa produces mineralocorticoids (aldosterone) and consists of cells arranged in rounded clusters or arches beneath the capsule.

Chromaffin cells (pheochromocytes) of the adrenal medulla contain catecholamines (epinephrine, norepinephrine) in membrane-bound granules.

The thyroid develops from endoderm at the foramen cecum (floor of pharynx between 1st and 2nd pharyngeal arches) during week 3-4.

Thyroid follicles are lined by simple cuboidal follicular cells (thyrocytes) surrounding a central lumen filled with colloid.

The superior parathyroids develop from the 4th pharyngeal pouch and have a short descent, so their position is relatively constant (posterior to middle thyroid).

Chief (principal) cells are the predominant parathyroid cells and secrete parathyroid hormone (PTH).

The inferior thyroid artery (branch of thyrocervical trunk) supplies both superior and inferior parathyroid glands in most cases (80%).

Both pancreatic buds arise from foregut endoderm.

Alpha cells produce glucagon and are located at the periphery of pancreatic islets, comprising 15-20% of islet cells.

Special stains like aldehyde fuchsin or modified Gomori stain differentiate islet cells: beta cells contain zinc-insulin complexes that stain blue/purple with these stains, while alpha cells (glucagon granules) stain red/pink.

Centroacinar cells are unique to the pancreas–they are small, pale-staining cells located within the center of acini, representing the extension of intercalated duct cells into the acinus.

The pancreatic head receives dual blood supply: superior pancreaticoduodenal arteries (from gastroduodenal artery/celiac trunk) and inferior pancreaticoduodenal arteries (from superior mesenteric artery).

Horseshoe kidney forms when the lower poles of metanephric kidneys fuse during the 5th-9th week as they ascend from the pelvis.

The metanephric mesenchyme (intermediate mesoderm) forms the nephrons–from Bowman’s capsule through the proximal convoluted tubule, loop of Henle, to the distal convoluted tubule.

The glomerular filtration barrier has three layers: (1) fenestrated capillary endothelium (lacks diaphragms, unlike other fenestrated capillaries), (2) glomerular basement membrane (GBM–fused basal laminae, contains type IV collagen, laminin, proteoglycans), (3) podocyte foot processes with filtration slits bridged by slit diaphragms (nephrin protein).

Proximal convoluted tubule (PCT) cells have a prominent brush border (microvilli for increased surface area) and basal striations (interdigitating lateral membranes with abundant mitochondria for ATP-dependent transport).

The JGA has three components: (1) macula densa–specialized DCT cells sensing sodium chloride concentration, (2) extraglomerular mesangial cells (lacis cells)–connecting macula densa to afferent arteriole, (3) juxtaglomerular (JG) cells–modified smooth muscle cells in afferent arteriolar wall containing renin granules.

The left renal vein is longer (crosses anterior to aorta) and receives the left gonadal vein (testicular/ovarian) inferiorly and the left suprarenal vein superiorly, plus the left inferior phrenic vein.

At the renal hilum, structures are arranged anterior to posterior as: Vein (most anterior), Artery (middle), and ureter/pelvis (most posterior and inferior).

Bilateral renal agenesis results from failure of the ureteric bud to develop or to induce the metanephric mesenchyme.

Ureteric buds arise from the caudal mesonephric (Wolffian) duct near its insertion into the cloaca.

The trigone is formed by absorption of the caudal mesonephric ducts into the developing bladder, giving it a mesodermal origin.

The detrusor muscle receives parasympathetic innervation via pelvic splanchnic nerves (nervi erigentes) from S2-S4 spinal segments, causing bladder contraction during micturition.

The bladder is lined by transitional epithelium (urothelium), which is specialized for distension.

The transition zone (surrounding the proximal urethra) is the site of benign prostatic hyperplasia (BPH), which causes urinary obstruction.

Prostatic glands have pseudostratified columnar epithelium with a layer of basal cells (stem cells for regeneration).

The prostatic (pelvic) plexus, part of the inferior hypogastric plexus, lies on the posterolateral surface of the prostate.

The prostate receives blood supply primarily from prostatic branches of the inferior vesical artery (branch of anterior division of internal iliac artery).

The male urethra has four parts: (1) preprostatic/intramural (within bladder wall), (2) prostatic (widest, through prostate), (3) membranous (shortest, narrowest, passes through urogenital diaphragm/external sphincter), (4) spongy/penile (longest, through corpus spongiosum).

Rupture of the membranous urethra (above the perineal membrane) causes urine to extravasate into the deep perineal pouch and may track into the retropubic space (of Retzius).

The female urethra is approximately 3-4 cm long (vs.

Posterior urethral valves are the most common cause of congenital lower urinary tract obstruction in males.

In females, ectopic ureters may open into the vagina, vestibule, or urethra below the external sphincter, causing continuous dribbling incontinence despite normal voiding (two drainage pathways).

The perineum is a diamond-shaped region bounded by the pubic symphysis anteriorly, tip of coccyx posteriorly, ischiopubic rami anterolaterally, sacrotuberous ligaments posterolaterally, and ischial tuberosities laterally.

The external anal sphincter is a voluntary skeletal muscle encircling the anal canal, supplied by the inferior rectal nerve (branch of pudendal nerve, S2-S4) and the perineal branch of S4.

The superficial perineal pouch (space) in females contains: bulb of vestibule (erectile tissue), crura of clitoris, greater vestibular (Bartholin’s) glands, ischiocavernosus and bulbospongiosus muscles, and branches of pudendal vessels/nerves.

The ischioanal fossa (ischiorectal fossa) is a fat-filled wedge-shaped space lateral to the anal canal and rectum.

The pudendal nerve (S2-S4) exits the pelvis through the greater sciatic foramen (inferior to piriformis), curves around the ischial spine and sacrospinous ligament, then re-enters the perineum through the lesser sciatic foramen.

The internal pudendal artery (from anterior division of internal iliac) is the main blood supply to the perineum.

The levator ani has three parts: pubococcygeus (pubovesicalis, puboprostaticus/pubovaginalis, puboanalis), puborectalis (forms U-shaped sling around anorectal junction maintaining continence), and iliococcygeus.

The puborectalis muscle forms a U-shaped sling around the anorectal junction, originating from the posterior pubic bone and looping behind the rectum without a posterior attachment.

The cardinal (transverse cervical/Mackenrodt’s) ligament is the primary support for the cervix and upper vagina, extending from the cervix/vaginal fornix to the lateral pelvic wall.

The ureter crosses inferior (under) to the uterine artery approximately 1.5-2 cm lateral to the supravaginal cervix at the level of the internal os, within the cardinal ligament.

The processus vaginalis is an outpouching of peritoneum that precedes testicular descent.

The gubernaculum is a fibrous cord connecting the testis to the scrotum that guides testicular descent.

Sertoli cells (sustentacular cells) are tall columnar cells within seminiferous tubules that support and nourish developing sperm.

The testicular artery arises directly from the abdominal aorta (below renal arteries) and descends through the inguinal canal.

The epididymis is lined by pseudostratified columnar epithelium with stereocilia (long, non-motile microvilli that absorb fluid).

The vas deferens has a characteristic structure: pseudostratified columnar epithelium (mucosa), a very thick muscular coat with three layers (inner longitudinal, middle circular, outer longitudinal), and an outer adventitia.

The seminal vesicles are paired glands posterior to the bladder that produce 60-70% of semen volume.

The prostatic utricle (Latin: “little uterus”) is a small blind pouch located at the verumontanum (colliculus seminalis) in the prostatic urethra, between the openings of the ejaculatory ducts.

The penis contains three erectile bodies: two corpora cavernosa (paired, dorsal, enclosed in thick tunica albuginea) and one corpus spongiosum (midline, ventral, contains penile/spongy urethra).

The tunica albuginea is a tough, thick sheath of dense irregular connective tissue (primarily type I collagen with some elastic fibers) that surrounds the corpora cavernosa.

The uterus, cervix, and upper two-thirds of the vagina develop from the paramesonephric (Müllerian) ducts.

A secondary follicle has multiple layers of granulosa cells (no longer a single layer as in primary follicle) and a developing antrum (fluid-filled cavity).

The corpus luteum (“yellow body”) forms from the remnants of the ovulated follicle.

The suspensory ligament (infundibulopelvic ligament) connects the ovary to the lateral pelvic wall and contains the ovarian vessels (artery from aorta, vein to IVC/renal vein), lymphatics, and autonomic nerves–must be ligated during oophorectomy.

The fallopian tube has dual blood supply: the ovarian artery (from aorta below renal arteries) supplies the lateral portion through tubal branches, while the uterine artery (from internal iliac) sends a tubal branch to the medial portion.

The fallopian tube is lined by simple columnar epithelium with two cell types: ciliated cells (beat toward uterus, propelling ovum and embryo) and peg/secretory cells (non-ciliated, produce nutrient secretions for ovum and sperm).

The uterine wall has three layers: endometrium (mucosa–simple columnar epithelium with underlying stroma containing glands), myometrium (thick smooth muscle in three layers), and perimetrium (serosa/visceral peritoneum–except lower anterior surface which has adventitia).

Day 21 is mid-secretory phase (days 15-28).

The ectocervix is lined by stratified squamous epithelium (non-keratinized), while the endocervical canal has simple columnar epithelium with mucus-secreting cells.

The vagina is lined by stratified squamous non-keratinized epithelium–similar to oral mucosa.

The vulva includes: mons pubis (fatty tissue over pubic symphysis), labia majora (homologous to scrotum), labia minora (no male homologue–derived from urogenital folds), vestibule (contains urethral and vaginal openings), clitoris (homologous to penis–has corpora cavernosa and glans), bulbs of vestibule (homologous to corpus spongiosum), greater vestibular glands (Bartholin’s–homologous to bulbourethral glands), and lesser vestibular glands (Skene’s–homologous to prostate).

The greater vestibular (Bartholin’s) glands are paired, pea-sized glands located deep in the posterior part of the labia majora, at approximately 4 and 8 o’clock positions relative to the vaginal orifice.

The uterine artery arises from the anterior division of the internal iliac artery.

The cervix and lower uterus drain primarily to external iliac and obturator lymph nodes (sentinel nodes for cervical cancer), then to common iliac and para-aortic nodes.

Uterine fibroids (leiomyomas) are benign tumors arising from smooth muscle cells of the myometrium.

The ovarian surface is covered by “germinal epithelium”–a misnomer as it doesn’t produce germ cells.

During fetal life, the adrenal cortex has a large inner fetal zone (80% of gland) that produces DHEA for placental estrogen synthesis.

The adrenal cortex (from mesoderm) develops before neural crest cells migrate into it to form the medulla.

Parathyroid glands appear yellow-brown (tan/mustard color), are soft, oval-shaped (approximately 5×3×1 mm), and lie on the posterior surface of the thyroid, outside its capsule but within the pretracheal fascia.

Parafollicular (C cells) originate from neural crest cells that migrate via the ultimobranchial body (from 4th/5th pharyngeal pouch) into the developing thyroid.

C cells are most concentrated at the junction of the upper and middle thirds of the lateral thyroid lobes–reflecting their origin from the ultimobranchial body that fuses at this location.

PTH acts on two nephron sites: (1) proximal convoluted tubule–inhibits phosphate reabsorption (phosphaturia) and stimulates 1α-hydroxylase (activating vitamin D); (2) distal convoluted tubule–increases calcium reabsorption (hypercalcemic effect).

Collecting ducts contain two cell types: (1) Principal cells (pale, with single cilium)–respond to aldosterone (sodium reabsorption, potassium secretion) and ADH (water reabsorption via aquaporins); (2) Intercalated cells (darker, with microvilli)–regulate acid-base balance.

Podocytes are specialized visceral epithelial cells with interdigitating foot processes (pedicels) that wrap around glomerular capillaries.

Juxtaglomerular (JG) cells are modified smooth muscle cells in the afferent arteriolar wall containing renin granules.

Multicystic dysplastic kidney results from abnormal interaction between the ureteric bud and metanephric mesenchyme, leading to abnormal induction of nephrons.

Potter facies results from oligohydramnios-induced fetal compression: low-set ears, flattened nose (from pressing against uterine wall), receding chin (micrognathia), prominent epicanthal folds, and wide-set eyes.

The Weigert-Meyer rule describes duplex kidney ureteral insertion: the upper pole ureter (from a ureteric bud arising higher on mesonephric duct) inserts inferomedially and may be ectopic (into bladder neck, urethra, or genital structures).

The detrusor muscle has three indistinct layers of smooth muscle: inner longitudinal, middle circular, and outer longitudinal.

The interureteric ridge (Mercier’s bar) is a muscular fold connecting the two ureteric orifices, forming the superior border of the trigone.

Epispadias (dorsal urethral opening) results from faulty positioning of the genital tubercle (more caudal than normal) or defective mesenchymal migration that fails to close the dorsal urethra.

Hypospadias results from incomplete fusion of the urethral folds over the urethral plate (ectodermal ingrowth that canalizes to form urethra).

The urethral folds fuse in males to form the ventral shaft of penis (covering the spongy urethra), while in females they remain unfused as the labia minora.

The pituitary gland lies in the sella turcica with the cavernous sinuses on either side.

The anterior pituitary (adenohypophysis) develops from Rathke’s pouch, an ectodermal upgrowth from the stomodeum (primitive oral cavity).

PAS-positive cells in the anterior pituitary are basophils, which include corticotrophs (ACTH), thyrotrophs (TSH), and gonadotrophs (FSH/LH).

The adrenal cortex (including zona glomerulosa, fasciculata, and reticularis) develops from intermediate mesoderm, specifically the urogenital ridge, which also forms the gonads.

The left adrenal vein drains into the left renal vein, making it shorter and requiring careful ligation during left adrenalectomy.

The zona reticularis (innermost cortical zone) receives blood via sinusoidal capillaries that have traversed the zona glomerulosa and fasciculata.

The thyroid gland descends from the foramen cecum at the base of the tongue, passing anterior to the hyoid bone and laryngeal cartilages to reach its final position at the C5-C7 vertebral level (overlying the 2nd-4th tracheal rings).

The external laryngeal nerve (branch of superior laryngeal nerve from vagus) runs with the superior thyroid artery before diverging to innervate the cricothyroid muscle.

Parafollicular C cells are derived from the ultimobranchial body, which originates from the fourth and fifth pharyngeal pouches (neural crest contribution).

The inferior parathyroid glands develop from the third pharyngeal pouch along with the thymus, explaining their variable position and occasional association with ectopic thymic tissue.

Oxyphil cells are larger than chief cells with abundant eosinophilic cytoplasm due to numerous mitochondria.

Superior parathyroid glands, developing from the fourth pharyngeal pouch, have a more predictable location posterior to the middle third of the thyroid lobe, approximately at the level of the cricoid cartilage.

Alpha cells constitute approximately 15-20% of islet cells and are predominantly located at the periphery of the islets (in humans, distribution is more heterogeneous than the traditional rodent model suggests).

Centroacinar cells are unique to the pancreas and represent the beginning of the intercalated duct system extending into the acinar lumen.

Annular pancreas results from abnormal rotation or bifid development of the ventral pancreatic bud.

The ventral pancreatic bud gives rise to the uncinate process and inferior part of the pancreatic head.

Podocytes (visceral epithelial cells of Bowman’s capsule) develop from the metanephric mesenchyme (metanephric blastema).

In horseshoe kidney, the inferior poles of the kidneys fuse across the midline (connected by an isthmus).

The thin limbs of the loop of Henle (both ascending and descending) are lined by simple squamous epithelium with few organelles, reflecting their passive transport functions.

In ADPKD, cysts can arise from any nephron segment, but most commonly originate from collecting ducts, which develop from the ureteric bud.

Ureteric peristalsis is initiated by atypical smooth muscle cells (pacemaker cells) located at the pelvi-ureteric junction.

The left renal vein receives the left gonadal vein, left suprarenal vein, and left inferior phrenic vein before draining into the IVC.

Kidney development requires reciprocal induction between the ureteric bud (outgrowth of mesonephric duct) and metanephric mesenchyme.

The detrusor muscle receives parasympathetic innervation from S2-S4 spinal segments via pelvic splanchnic nerves (nervi erigentes).

The external urethral sphincter (sphincter urethrae) is skeletal muscle under voluntary control, innervated by the pudendal nerve (S2-S4).

The prostate gland develops from the urogenital sinus (endoderm) under influence of dihydrotestosterone from fetal testes.

Posterior urethral valves are most commonly Type I valves located in the prostatic urethra distal to the verumontanum (the elevation where ejaculatory ducts open).

In duplex collecting systems, two ureteric buds arise from the mesonephric (Wolffian) duct.

The bladder trigone develops from incorporated mesonephric (Wolffian) duct tissue, which is mesodermal in origin.

The urachus is the remnant of the allantois, an outpouching of the yolk sac that extends into the connecting stalk.

Multicystic dysplastic kidney (MCDK) results from failure of the ureteric bud to properly induce differentiation of the metanephric mesenchyme.

The cavernous nerves (responsible for erection) arise from the inferior hypogastric (pelvic) plexus located lateral to the rectum, prostate, and bladder.

The deep transverse perineal muscle is located in the deep perineal pouch (urogenital diaphragm), not the superficial pouch.

The internal pudendal artery, a branch of the internal iliac artery, enters the perineum through the lesser sciatic foramen along with the pudendal nerve and internal pudendal vein in Alcock’s canal.

The external anal sphincter is innervated by the inferior rectal (inferior hemorrhoidal) branch of the pudendal nerve (S2-S4).

The pudendal nerve arises from S2, S3, S4 (anterior rami) and provides sensory innervation to the perineum (external genitalia, perineal skin) and motor innervation to the external urethral sphincter, external anal sphincter, and perineal muscles.

The ischiorectal (ischioanal) fossa has an anterior recess that extends above the urogenital diaphragm (deep perineal pouch) between the levator ani medially and obturator internus laterally.

The iliococcygeus (part of levator ani) arises from the tendinous arch of levator ani (arcus tendineus levator ani), a thickening of the obturator fascia extending from the pubis to the ischial spine.

Denonvilliers’ fascia (rectovesical septum) is the remnant of fusion of peritoneum from the rectovesical pouch and represents the fused layers derived from the embryological cloaca division by the urorectal septum.

Mediolateral episiotomy angles away from the midline to avoid damage to the external anal sphincter and anal canal located posteriorly in the perineal body.

Sertoli cells develop from the surface (coelomic) epithelium of the gonadal ridge, which proliferates to form sex cords that surround the primordial germ cells.

Leydig (interstitial) cells develop from the mesenchyme (intermediate mesoderm-derived) of the gonadal ridge.

The testis descends through the inguinal canal guided by the gubernaculum, accompanied by the processus vaginalis (an evagination of peritoneum).

The testicular artery arises directly from the abdominal aorta at the L2 level (reflecting the original retroperitoneal position of the developing testis).

Left varicocele is more common because the left testicular vein is longer, drains at a right angle into the left renal vein (higher resistance), and has less competent valves compared to the right testicular vein which drains obliquely into the IVC.

The ejaculatory ducts pass through the central zone of the prostate (approximately 25% of prostate volume) to open at the verumontanum (seminal colliculus) in the prostatic urethra.

The prostatic venous plexus communicates with the internal vertebral venous plexus (Batson’s plexus), a valveless system extending along the vertebral column.

The vas deferens develops from the mesonephric (Wolffian) duct under the influence of testosterone.

Stereocilia (long immotile microvilli) in the epididymis absorb testicular fluid and secrete substances necessary for sperm maturation and storage.

Erection is initiated by parasympathetic fibers from S2-S4 via pelvic splanchnic nerves, which synapse in the pelvic plexus and send cavernous nerves along the posterolateral aspect of the prostate to the corpora cavernosa.

In complete androgen insensitivity syndrome (CAIS), testes are present and produce both testosterone and anti-Müllerian hormone (AMH).

The ovarian artery arises from the abdominal aorta at approximately L2 level, reflecting the original retroperitoneal position of the developing ovary near the kidney.

The ureter passes approximately 2 cm lateral to the cervix and is crossed superiorly by the uterine artery (“water under the bridge” – ureter under the artery).

The uterus receives autonomic innervation from the inferior hypogastric (pelvic) plexus, containing both sympathetic (from hypogastric nerves) and parasympathetic (from pelvic splanchnic nerves) fibers.

The endocervical canal is lined by simple columnar (mucus-secreting) epithelium, which meets the stratified squamous epithelium of the ectocervix at the squamocolumnar junction (transformation zone).

The fallopian tube is lined by simple columnar epithelium with two cell types: ciliated cells (beating toward the uterus to propel the ovum) and non-ciliated secretory (peg) cells that provide nutrients for the gametes and early embryo.

The uterine artery (branch of internal iliac) runs along the lateral border of the uterus and gives off arcuate arteries that penetrate the myometrium.

The granulosa cells are separated from the theca cells by a basement membrane (membrana granulosa).

The vagina lacks glands in its wall.

Bartholin’s glands (greater vestibular glands) are paired, pea-sized glands located in the superficial perineal pouch posterolateral to the vaginal orifice at approximately the 4 and 8 o’clock positions.

The vagina develops from two sources: the upper vagina from the fused paramesonephric ducts (uterovaginal canal) and the lower vagina from the sinovaginal bulbs arising from the urogenital sinus.

A transverse vaginal septum occurs at the junction of the upper vagina (from the uterovaginal canal/paramesonephric ducts) and lower vagina (from sinovaginal bulbs/urogenital sinus).

The epoophoron (along with the paroophoron) is a vestigial remnant of the mesonephric (Wolffian) duct located in the mesosalpinx between the ovary and fallopian tube.