3 - Embryology of the Urinary System Flashcards
What is the ligament that holds the bladder to the anterior abdominal wall?
Urachus/Median Umbilical Ligament: fibrous remnant of the allantois, a canal that drains the urinary bladder of the fetus that joins and runs within the umbilical cord
In general terms, how is the embryology of the urinary system split up?
- Kidney and Ureters from intermediate mesoderm
- Bladder and Urethra from caudal hindgut
In general terms, what are the three stages of kidney development?
- From intermediate development in the urogenital ridge
- One system disappears as the other appears
What is the urogenital ridge?
Area of intermediate mesoderm giving rise to embryonic kidney and the gonad
Explain in detail the three stages of kidney developments.
Week 4: Pronephros never functional but its duct from cervical region to cloca drives differentiation of mesoderm to mesonephric tubules
End of Week 4 - Week 8: Mesonephric duct (ureteric bud) and mesonephric tubules (future nephrons) make the embryonic kidney but it has no water conserving mechanism. Filtrate from tubules drains into cloaca.
Week 5: Ureteric bud sprouts from mesonephric duct, which causes undifferentiated intermediate mesoderm to differentiate, forms metanephric blastema.
What happens to the pronephric and mesonephric ducts once they have completed their function?
- Pronephric regresses
- Mesonephric duct stays if XY to form male reproductive system or regresses if XX
Where does the primitive kidney first appear and where does it change position to?
- Metanephric blastema in the pelvic region near cloaca
- Cranio-caudal shift from L4 to L1/T12
- Lateral displacement to join with adrenal glands
- 90 degrees rotation so renal pelvis faces midline
- Kidney crosses arterial fork formed by umbilical vessels
How does the blood supply to the kidneys change during it’s ascent?
As kidney moves up more vessels form and old ones degenerate
Why do the gonad and kidney effectively switch positions in fetal development?
What are some issues that can occur when the kidney goes on its ascent?
Accessory arteries are end arteries so can lead to damage of kidney segments if ischaemic. Arteries can also block ureter causing hydronephrosis
What is hydronephrosis?
Swelling of a kidney due to build-up of urine. Cannot drain out from the kidney to the bladder from a blockage or obstruction
What is a horseshoe kidney?
Two metanephric kidneys caudal poles touch and fuse on ascent so join by an isthmus. Get stuck on unpaired branch of the aorta so issue migrating. Can be asymptomatic
What are some issues that can occur as the ureteric bud sprouts?
- Renal Agenesis: Ureteric bud fails to sprout or ineract with intermediate mesoderm. If bilateral can’t survive
- Multiple ureteric buds, can lead to ectopic ureter
- Cystic Disease
What is an issue with a duplex ureter?
- May lead to extra lobe of a kidney, which can lead to hydronephrosis
- Ureter could go into vagina, no control by the EUS so no control over mituration.
- Ureterocoele (Jenna’s case)
Where does the bladder and the urethra originate from?
Urogenital sinus which comes from the far end of the hindgut, cloaca, in 4th week of development.
What is the structure of the cloaca and the allantois?
- Cloaca: blind end separated from outside world by cloacal membrane. Meso-dermless region
- Allantois: superoventral diverticulum of the hindgut that stretches into the umbilicus. Lumen becomes obliterated to become the urachus
Cloaca gets divided by urorectal septum to form urogenital sinus and anorectal canal
What is the urorectal septum?
Wedge of mesoderm in the cloacal membrane. Forms the perineal body and the pelvic floor
How does the urethra form?
- Narrowing of the lower urogenital sinus, with the distal part becoming the external genitalia
Males: distal urethra elongated to become spongy urethra and penis develops by urethal folds under male sex hormone influence
Females: Urethra opens into vestibule of vagina because urethral folds do not fuse
How do the ureters connect to the bladder in females?
How do the ureters connect to the bladder in males?
What are the different parts of the male urethra?
What is hypospadias?
- Defect in fusion of the genital folds (tissue surrounding UGS)
- Urethra opens onto ventral surface of penis rather than at glans
- Increasing incidence
What is bladder exstrophy?
Congenital abnormality where skin over the lower abdominal wall does not form properly. Bladder open and exposed on the outside of the abdomen.
Cloacal membrane is not replaced by tissue that will form the abdominal muscles
What are urachal anomalies?
- Urachus fails to close off so issue anywhere from bladder to umbilicus.
- Common to get urachal cysts and wetness from umbilicus. Cysts can present with UTI, haematuria, painful urination, vomiting
