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Lecture 10

Outline of Lecture 10

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Dirk De Clercq

Outline of Lecture 10 Urogenital Development 0. Overview - Urogenital system arises from intermediate mesoderm - Both systems have common components (processing, ducts, storage, excretion outlet) I. Urinary System A. Pronephros th - Most cranial, nonfunctional, and regresses by end of 4 week B. Mesonephros - Nephrotomes develop into functional mesonephric units (bulges give UG ridges) - Mesonephric units contain mesonephric tubules (connected to developing mesonephric duct) and Bowman’s capsule (surrounding glomerulus) - Initially, mesonephric kidney empties into intraembryonic cavity, but after mesonephric duct forms it empties into cloaca - Mesonephros regresses by 3 month, leaving behind mesonephric duct C. Metanephros 1. Collecting system - Ureteric bud arises from mesonephric duct, and becomes metanephric duct - Successive bifurcations gives rise to renal pelvis, major and minor calyces, and collecting tubules (of renal pyramids) 2. Excretory system - Renal vesicles give rise to renal tubules, which establish connection with collecting tubule and give rise to middle part of nephron - Remember, urine passes through mesonephric duct on way to cloaca D. The kidney ascends in the abdomen during development E. Development of the bladder and urethra - Week 6-7, urorectal septum divides cloaca into anorectal canal and urogenital sinus - UG sinus develops into bladder, prostatic and membranous urethra, and phallic urethra - Allantois  urachus  median umbilical ligament - Mesonephric ducts furse to become prostatic urethra - Ureters fuse at trigone of bladder (originally mesoderm, replaced by endoderm) F. Congenital disorders urinary system - Congenital cystic kidney: collecting tubules and renal tubules don’t connect - Renal agenesis: ureteric bud degenerates, no kidney, fatal - Double or ectopic ureter: early ureteric bud splits, two ureters form - Pelvic or horseshoe kidney: caudal kidney poles fuse, ascension stopped by IMA - Urachal fistula: allantois lumen persists II. Genital System A. Formation of gonads 0. Indifferent stage (approx. weeks 3-7) - Coelomic epithelium gives rise to primitive sex cords - Germ cells arrive at genital ridge week 6, when gonads start to differentiate 1. Male testis - Primitive sex cords develop into medullary cords, which give rise to rete testis; in 4 month cords made of PGCs and Sertoli cells (make MIS); in puberty, cords develop lumen and become seminiferous tubules
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