[EMBRYOLOGY] Chapter 16 Urogenital System

"Pronephros"

"The first, rudimentary and nonfunctional kidney system; 7-10 solid cell groups in the cervical region during week 4, fully disappeared by end of week 4."

"Mesonephros"

"Second kidney system; forms S-shaped excretory tubules with glomeruli from intermediate mesoderm (upper thoracic to L3), draining into the mesonephric duct; functions briefly in early fetal life."

"Metanephros"

"The definitive, permanent kidney; appears in week 5 and forms from two sources: metanephric mesoderm (nephrons) and the ureteric bud (collecting system)."

"Urogenital ridge"

"Structure formed by the mesonephros and the developing gonad lying together along the posterior abdominal wall."

"Mesonephric (Wolffian) duct"

"Longitudinal duct draining the mesonephros; persists in males to help form the male genital duct system, degenerates in females."

"Ureteric bud"

"Outgrowth of the mesonephric duct that penetrates metanephric mesoderm and gives rise to the ureter, renal pelvis, calyces, and collecting ducts."

"Metanephric mesoderm (blastema)"

"Mesenchymal tissue induced by the ureteric bud to form nephrons (excretory units) of the permanent kidney."

"WT1"

"Transcription factor expressed by metanephric mesenchyme that makes it competent to respond to ureteric bud induction; also regulates GDNF/HGF production; mutated in Wilms tumor."

"GDNF"

"Glial-derived neurotrophic factor produced by metanephric mesenchyme; binds RET receptor on the ureteric bud to stimulate its growth and branching."

"HGF (scatter factor)"

"Hepatocyte growth factor from metanephric mesenchyme; binds MET receptor on the ureteric bud to stimulate growth."

"FGF2 and BMP7"

"Growth factors from the ureteric bud that stimulate proliferation of metanephric mesenchyme and maintain WT1 expression."

"WNT9B and WNT6"

"Signals from the ureteric bud that upregulate PAX2 and WNT4 in metanephric mesenchyme, driving tubule formation."

"PAX2"

"Gene upregulated by WNT9B/WNT6 that promotes condensation of metanephric mesenchyme in preparation for tubule formation."

"WNT4"

"Gene that causes condensed metanephric mesenchyme to epithelialize and form tubules; also the master ovary-determining gene later in the chapter."

"Wilms tumor"

"Pediatric kidney cancer due to WT1 gene mutation (11p13); usually presents by age 5."

"WAGR syndrome"

"Wilms tumor, Aniridia, Gonadoblastoma, mental Retardation — caused by a microdeletion spanning both PAX6 and WT1 on chromosome 11."

"Denys-Drash syndrome"

"Triad of renal failure, ambiguous genitalia, and Wilms tumor."

"ARPKD"

"Autosomal recessive polycystic kidney disease; cysts form from collecting ducts, kidneys enlarge greatly, renal failure in infancy/childhood; occurs in 1/5,000 births."

"ADPKD"

"Autosomal dominant polycystic kidney disease; cysts form from all nephron segments, renal failure typically delayed to adulthood; more common (1/500-1/1,000 births) but less severe than ARPKD."

"Potter sequence"

"Anuria, oligohydramnios, and hypoplastic lungs from bilateral renal agenesis (1/10,000 births); causes flattened Potter facies and clubfeet."

"Horseshoe kidney"

"Fusion of the lower poles of the kidneys during ascent, caused by passage through the arterial fork of the umbilical arteries; occurs in 1/600 people."

"Urorectal septum"

"Mesoderm dividing the cloaca into the urogenital sinus (anterior) and anal canal (posterior) during weeks 4-7."

"Urachus"

"Fibrous cord remaining after the intraembryonic allantois obliterates; connects bladder apex to umbilicus; becomes the median umbilical ligament in adults."

"Trigone of the bladder"

"Region formed by incorporation of the mesonephric ducts/ureters; initially mesodermal, later replaced by endodermal epithelium."

"Bladder exstrophy"

"Ventral body wall defect exposing bladder mucosa, always with epispadias; caused by failure of lateral body wall fold closure in the pelvis (2/10,000 births)."

"Cloacal exstrophy"

"More severe ventral body wall defect than bladder exstrophy, with urorectal septum abnormalities and widely spaced genital swellings; rare (1/30,000)."

"SRY gene"

"Sex-determining region Y gene (Yp11); master switch transcription factor initiating the testis-determining cascade."

"Primordial germ cells"

"Cells originating in the epiblast that migrate through the primitive streak, reside near the yolk sac/allantois, then travel via the dorsal mesentery of the hindgut to the genital ridges by week 5-6."

"Indifferent gonad"

"Early gonad stage with primitive sex cords, histologically identical in both sexes prior to SRY-driven differentiation."

"Leydig cells"

"Interstitial testicular cells derived from gonadal mesenchyme; begin producing testosterone by week 8."

"Paramesonephric (Müllerian) duct"

"Duct system that becomes the female genital tract (uterine tubes, uterus, cervix, upper vagina) in the absence of AMH."

"Anti-Müllerian hormone (AMH/MIS)"

"Hormone from Sertoli cells that causes regression of the paramesonephric ducts in males."

"SOX9"

"Autosomal transcriptional regulator acting with SRY to drive testis differentiation and regulate AMH expression."

"SF1"

"Steroidogenesis factor 1; upregulated by SRY/SOX9, elevates AMH and stimulates testosterone-synthesizing enzymes in Leydig cells."

"DAX1"

"Gene upregulated by WNT4 in females that inhibits SOX9, allowing ovarian differentiation to proceed."

"Dihydrotestosterone (DHT)"

"Androgen converted from testosterone by 5-alpha-reductase; drives differentiation of the male external genitalia."

"Genital tubercle"

"Indifferent-stage midline swelling that becomes the phallus/glans in males or the clitoris in females."

"Hypospadias"

"Incomplete fusion of the urethral folds causing abnormal ventral urethral openings on the penis; occurs in 3-5/1,000 births."

"Epispadias"

"Rare defect (1/30,000) with the urethral meatus on the dorsum of the penis; strongly associated with bladder exstrophy."

"Congenital adrenal hyperplasia (CAH)"

"Most common cause of ambiguous genitalia (~60% of DSDs); usually from 21-hydroxylase deficiency causing excess adrenal androgens in 46,XX individuals."

"Androgen insensitivity syndrome (AIS)"

"46,XY individuals with testes and normal AMH (so no uterus/tubes) but non-functional androgen receptors, preventing external genital virilization."

"Swyer syndrome"

"XY female gonadal dysgenesis from SRY mutation/deletion; phenotypic female with streak gonads, no menstruation or secondary sex characteristics."

"Gubernaculum"

"Mesenchymal band guiding testicular descent from the abdomen through the inguinal canal into the scrotum."

"Processus vaginalis"

"Peritoneal evagination following the gubernaculum into the scrotum; becomes the tunica vaginalis; if it stays open, causes inguinal hernia or hydrocele."

"Cryptorchidism"

"Failure of one or both testes to descend into the scrotum; affects