The development of kidneys, ureters, bladder, and urethra is primarily from intermediate mesoderm.
Origin: Intermediate mesoderm (between paraxial and lateral plate mesoderm)
Timeline: Begins around week 4 of gestation
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