Development of the Urogenital System

Question 1

Which mesoderm does the urogenital tract originate from?

Answer 1

Intermediate.

Question 2

Which direction do the kidney structures form?

Answer 2

Cranial to caudal.

Question 3

Name the 3 kidney structures in development? What week do they arise?

Answer 3

Pronephros - gone by week 4.
Mesonephros
Metanephros (definative kidney) - Arises in week 5 and is functional by week 11.

Question 4

Describe kidney development?

Answer 4

PRONEPHROS (week 4): Arises in the cervical region as 7-10 solid cell groups. It is rudimentary and non-functional. It regresses by week 4.

MESONEPHROS: Derived from thoracic and lumbar segments. After the pronephros starts to regress, the first excretory tubules of the metanephros appear. Contributes supporting cells to the genital ridge.

METANEPROS: Appears in week 5 and functional by week 11. Excretory units form from the metanephric mesoderm.
2 units;
- Ureteric bud: Outgrowth of the mesonephric duct which is the source of all the duct system. Allows urine drainage from the developing kidney.
Metanephric cap which surrounds the bud and provides excretory units.

Question 5

Which 2 parts form the kidney (metanephros)?

Answer 5

Ureteric bud and metanephric cap.

Question 6

When does the bladder and urethra form?

Answer 6

Weeks 4-7

Question 7

How does the bladder and urethra form?

Answer 7

The cloaca (endoderm) gets divided by the urorectal septum as it fuses with the cloaca membrane. It forms to anterior urogenital sinus and posterior anal canal. 
The bladder forms from the urogenital sinus and caudal mesonephric duct. 
The endoderm from cloaca forms the bladder lining.

Question 8

In which week do the gonads acquire male or female characteristics?

Answer 8

Week 7.

Question 9

Describe the ‘Indifferent Stage’ of genital duct development?

Answer 9

Weeks 5-6.
2 pairs of genital ducts develop;
- The Paramesonephric (Mullerian) ducts.
- The Mesonephric (Wolffian) ducts.

Question 10

What is the function of the Wolffian ducts? What causes them to develop/regress?

Answer 10

Drain urine from the mesonephric kidney.

Testosterne causes the duct to form the ductus deferens and the ejaculatory duct. They regress in females due to a lack of testosterone.

Question 11

Which genital duct is more lateral?

Answer 11

Mullerian (paramesonephric ducts)

Question 12

Describe development of the mullerian duct?

Answer 12

Forms a funnel shaped cranial end which opens into the peritoneal cavity. They migrate caudally until they reach the pelvic region, before approaching each other in the midline.
The cranial portion forms the uterine tubes and the caudal portion fuses to form the uterovaginal primordium (uterus and sup. vagina).
In the male, they regress to to the action of anti-mullerian hormone.

Question 13

What makes anti-mullerian hormone?

Answer 13

Sertoli cells in the developing testis.