43 Development of the urogenital system

Question 1

When does bilaminar disc form and what does it form into?

Answer 1

Conceptus about 12 days post fertilisation implanted in uterine mucosa

Forms hypoblast and epiblast

Question 2

When does bilaminar disc become trilaminar (gastrulation) and what 3 layers does it form?

Answer 2

In early stages of development (2 weeks post conception)

3 layers formed in week 3 are ectoderm, endoderm and mesoderm

Question 3

What is the allantois?

Answer 3

• Vestigial structure
• Waste storage
• From ventral region of urogenital sinus to umbilicus
• Distal portion called urachus which becomes median umbilical fold

Question 4

What is the urorectal septum (mesodermal)?

Answer 4

• Seperation of cloaca
• Anteriorly as urogenital sinus that is continuous with allantois
• Posteriorly as the anorectal canal

Question 5

What does the cloaca develop into?

Answer 5

• Anteriorly: urogenital system (urinary bladder, urethra and lower urogenital tract
• Posteriorly: anorectal canal (rectum and upper anal canal)

Question 6

What structure becomes the posterior abdominal wall?

Answer 6

Mesoderm: lateral folding that enclose intra-embryonic coelom (peritoneal cavity)

Question 7

How does the mesoderm form the peritoneal cavity and posterior abdominal wall in development?

Answer 7

1. The mesoderm forms somites adjacent to the notochord and developing neural tube.
2. These form intermediate and lateral plate mesoderm
3. The lateral plate mesoderm cavitates to form the coelom
4. Folding moves the intermediate mesoderm to the posterior abdominal and pelvic wall
5. Coelom becomes peritoneal cavity

Question 8

What are the two points from which urinary and reproductive systems begin development?

Answer 8

1. Mesoderm and coelomic epithelium of the posterior abdominal wall
2. Endodermally derived cloaca (divided by the urorectal septum) and the allantois

Question 9

What 3 slightly overlapping kidney systems are formed sequentially from cranial to caudal within the mesoderm of the posterior abdominal and pelvic wall?

Answer 9

1. Pronephros - non-functional
2. Mesonephros - may be functional for a short time
3. Metanephros - definitive kidney

Question 10

What does mesonephros drain into and when?

Answer 10

Mesonephric ducts (Wolffian ducts; paired structure)

Week 4

Question 11

Where do the mesonephric ducts open into?

Answer 11

Cloaca

Divided by the urorectal septum into:
Anteriorly: Urogenital sinus and allantois
Posterioly: Anorectal canal

Question 12

When and how are the metanephros formed?

Answer 12

By about week 5, the ureteric bud (paired structure) extends form the caudal mesonephric duct (Wolffian duct)

Metanephric blastema also form (paired structure)

Metanephros develops in the pelvis from the ureteric bud and the metanephric blastema

Metanephros will become the definitive kidney

Question 13

What structures arise form ureteric bud?

Answer 13

Ureter
Calyces
Collecting ducts

Question 14

Ureter
Calyces
Collecting ducts

Answer 14

Renal tissue

i.e. glomeruli and loops of Henle

Question 15

When is the kidney functional?

Answer 15

Week 10

Question 16

What happens if the collecting ducts do not meet the nephrite vesicles?

Answer 16

Renal cysts form within the kidney

Question 17

What 2 abnormalities can occur when the kidney ascend from the pelvis up the posterior abdominal wall?

Answer 17

1. Pelvic kidney (1 risen, 1 in pelvic)

2. Horseshoe kidney (1 fused kidney in the pelvis)

Question 18

What is the consequence of abnormal branching of the ureteric bud before it reaches the metanephric blastema?

Answer 18

Bifid ureter

Question 19

What occurs when the ureteric bud fails to branch at all within the metaneprhic blastema?

Answer 19

Renal genesis - prevent kidney development