Embryogenesis of the Urinary System involves the development of kidneys, ureters, bladder, and urethra, primarily from intermediate mesoderm.
Origin: Intermediate mesoderm (between paraxial and lateral plate mesoderm)
Timeline: Begins around week 4 of gestation
Three successive kidney systems develop in a cranial-to-caudal sequence:
Nonfunctional in humans
Appears in the cervical region
Degenerates quickly
Temporarily functional (produces urine)
Located in thoracolumbar region
Contains mesonephric tubules and mesonephric (Wolffian) duct
The mesonephric duct contributes to male reproductive tract
Functional by week 9–10
Forms from:
Ureteric bud (from mesonephric duct): forms collecting system
Ureter, renal pelvis, major and minor calyces, collecting ducts
Metanephric mesenchyme (metanephric blastema): forms nephron
Bowman's capsule, PCT, loop of Henle, DCT
Reciprocal induction between the ureteric bud and metanephric mesenchyme is crucial.
Initially in pelvic region → ascend to lumbar position (by week 9)
Undergo 90° medial rotation
Renal arteries are re-supplied at different levels during ascent
Develops from ureteric bud
Derived from urogenital sinus (endoderm)
Continuous with allantois → becomes urachus → median umbilical ligament
Trigone: mesodermal origin (from mesonephric ducts), incorporated into bladder wall
Also from urogenital sinus
Female: entire urethra from pelvic part
Male: proximal urethra from pelvic part; distal from phallic part + ectodermal invagination (glandular urethra)
Renal agenesis: failure of ureteric bud to induce mesenchyme
Polycystic kidney disease: abnormal tubule development
Horseshoe kidney: fusion of inferior poles; ascent blocked by IMA
Ectopic ureter, duplicated ureter: from abnormal ureteric bud branching