Week 1: urogenital development

Question 1

Describe embryonic origins of bladder and urethra.

Answer 1

• from endoderm
• allantois is hindgut (endodermal) projection which extends from cloaca into umbilicus
• urorectal septum divides hindgut into GI and UG component
• embryonic component of allantois becomes future bladder, and distally forms cord from bladder to umbilicus (urachus) which becomes median umbilical ligament
• hindgut constriction–>pelvic urethra, and after constriction is the urogenital sinus

Question 2

Describe the formation of the kidneys.

Answer 2

• derived from intermediate mesoderm
• day 22: pronephros forms and regresses on day 25, never functional
• mesonephros forms and becomes function, then regresses (4,6,10th week)
• the mesonephric duct fuses with cloaca
• metanephros forms, becomes functional, persists (5, 10th week)–>becomes kidneys
• the ureteric bud (becomes ureters/collecting ducts)from mesonephric duct, surrounded by metaneprhic mass of mesoderm (becomes nephrons)

Question 3

How does the bladder get its shape?

Answer 3

• caudal ends of mesonephric ducts expand and move posteriorly, results in ureters drawn into bladder instead of opening into mesonephric ducts
• the caudal ends of mesonephric duct form trigone of bladder: triangular area on posterior inferior wall of bladder

Question 4

Describe the repositioning of the kidneys.

Answer 4

• in 6-9th weeks, kidneys ascend from sacral to lumbar position (really the caudal end of embryo grows grows and descends)
• caudal renal arteries degenerates, but sometimes persist as accessory renal arteries
• adrenal glands form in ultimate positions, don’t ascend with kidneys

Question 5

Describe fetal urine elimination.

Answer 5

• 7th week, UG membrane breaks down and urinary system continuous with external environ. (amniotic fluid)
• cycle of embryo ingesting amniotic fluid and reabsorbing it and passing out urinary system again
• waste eliminated when fetal blood passes through placenta

Question 6

Describe male internal genital development.

Answer 6

• paramesonephric ducts regresses
• gonads separates form mesonephros, gonads canalized to form seminiferous tubules and rete testis
• persisting mesonephric tubules become efferent ductule, each duct becomes epidymis and more distal the vas defense
• testes descends in 3rd month and again in 8-9th month

Question 7

Describe female internal genital development.

Answer 7

-paramesonephric ducts maintained
-mesonephric ducts regress
-paramesonephric ducts fuse in area of uterovaginal primordial, and penetrate dorsal side of urogenital sinus/urethra. Fusion moves cranially.
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Question 8

Identify the homologous structures between male and female genital structures.

Answer 8

Fetal structure: Male/female

• gonad: testes/ovary
• outgrowth from pelvic urethra: prostrate/urethral and paraurethral glands
• outgrowth from UG sinus: bulbourethral gland/greater vestibular glands
• UG sinus: penile urethra/vestibule of vagina
• genital tubercle: glans and shaft of penis/glans and shaft of clitoris
• UG folds: penis surrounding penile urethra/labia minor
• labioscrotal swellings: scrotum, labia majora.