GU embryology

Structure Male Female
Mesoderm
Pronephros

Excretory unit weeks 0-4
Degenerates after week 4
Mesonephros
(Wolffian duct)		 Excretory unit weeks 4-8
Degenerates after week 8 (unless +testosterone from Leydig cells → epididymis, vas deferens, seminal vesicles, ejaculatory ducts). Absent vas deferens (mesonephric duct) is associated with ipsilateral renal agenesis.
Ureteric bud arises from distal Wolffian duct at week 5
Distal portion is absorbed by UG sinus and becomes bladder trigone
Mesonephros
(genital ridge)		 Testis (+SRY) Ovary (-SRY)
Metanephros Excretory unit weeks >8
  1. Ingrowth of ureteric bud induces differentiation into nephrons
  2. Migrates from sacral to lower thoracic
    1. failure of ascension = pelvic kidney
    2. fusion of lower poles = horseshoe kidney, snagged on IMA
    3. incomplete diaphragm closure (Bochdalek's hernia) → continued ascension into chest = thoracic kidney)
  3. Rotates internally 90°
  4. Revascularizes successively during ascent (iliac → aorta); can leave multiple renal vessels if plexus does not degenerate
Mature kidney
Ureteric bud Arises during week 5 from distal posterior medial mesonephric/Wolffian duct (ureter)
Remains solid cord until week 6 before canalizing - starts from midsection and progresses cranially/caudally.  Ureteral atresia → MCDK (early), UPJ obstruction (late)
Bifurcates repeatedly during renal ascension → pelvis, calyces, infundibula, collecting ducts (anomalies → complete/incomplete duplication; absence → renal agenesis)
Induces metanephros → kidney
Paramesonephric
(Mullerian duct)		 Degenerates (MIF from Sertoli cells) Fallopian tubes, uterus, cervix, upper 1/3 of vagina
Genital tubercle* Penis Clitoris
Cloacal folds Penile urethra Labia minora
Adrenal cortex  
Endoderm
Urogenital sinus*

Prostatic urethra
Cowper's glands
Prostate
Part of bladder
Urachus

 

Entire urethra
Bartholin's glands
Skene's glands
Part of bladder
Urachus, hymen, lower 2/3 of vagina
Genital swellings* Scrotum Labia majora
Ectoderm
Adrenal medulla Sympathetic cells migrate and become encapsulated by cortex (which is of mesodermal origin, while medulla is from ectoderm)

*DHT causes male differentiation of external genitalia

  • Urogenital sinus: Rathke's plicae and Tourneux's fold form septum that separates cloaca into UG sinus and anorectal canal

Abnormal renal development

Complete duplication of collecting system (2 ureteral buds from Wolffian duct) - Weigert-Meyer law

  • Lower pole ureter inserts lateral/superior
    • More likely to reflux; have UPJ obstruction
  • Upper pole ureter inserts medial/inferior
    • More likely to be obstructive; ectopic
    • Commonly a/w ureterocele 
  • Upper pole is about 1/3 of the renal function of that kidney, not 1/2; usually just one calyx

Ectopic UO (does not insert into trigone)

  • F > M; present with UTI
  • Commonly in bladder neck or proximal urethra
    • Boys - always proximal to urinary sphincter (no incontinence) - posterior urethra, seminal vesicles
      • Usually not a/w duplicated system.
      • Can present as epididymitis - reflux into ejaculatory system (get imaging for repeated epididymitis in boys)
    • Girls - frequently distal to urinary sphincter (+ continuous incontinence) - urethra, vestibule, vagina, uterus
      • Usually a/w duplicated system
  • Diagnose with MR urogram
  • Treat with - reimplantation, ureteroureterostomy, or nephrectomy if nonfunctional

Posterior urethral valves - 2/2 abnormal insertion of Wolffian duct into cloaca, ?, incomplete dissolution of urogenital membrane

 

author: admin | last edited: May 26, 2020, 6:47 p.m. | pk: 39