Dev of Urinary System

Question 1

Renal agenesis- what is it and what is it associated with?

Answer 1

Uteric bud fails to develop, so no kidneys.

*Associated with oligohydramnios because can’t urinate, which also results in hypoplastic lungs

Question 2

The kidney originates from what germ layer?

Answer 2

Intermediate mesoderm (caudal part)

Question 3

3 stages of kidney development

Answer 3

1. Pronephros
   
   1. Tubules drain to the mesonephric duct, which becomes part of the genital system.
2. Mesonephros forms
   
   • Mesenchymal mass called metanephric blastema/nephrogenic cord will give rise to the metanephric kidney.
     
     • can also cause abnormal gonads
3. Metanephros forms
   
   1. Gonads develop
   2. Pronephros disappears
   3. Mesonephric duct gives rise to an epithelial outgrowth called ureteric bud, which will communicate with the metanephric blastema to induce formation of the kidney.

Question 4

Ureteric bud arises from ___, enters the ___ , andbecomes ___.

Answer 4

Ureteric bud

• arises from mesonephric duct,
• enters the metanephric blastema.
• becomes the ureters, renal pelvis, major calyces, minor calyces, and collecting ducts.

Question 5

How are collecting ducts and nephrons formed?

Answer 5

Collecting ducts are formed by the ureteric bud branching within the kidney.

The ducts will induce the mesenchyme around it to form the nephrons (glomerulus, prox tubule, loop of henle, dist tubule)

Question 6

How does the mesenchyme induce ureteric bud outgrowth from the Wolffian/nephric duct? How does it induce ureteric bud branching?

Answer 6

Mesenchyme releases GDNF (ligands), which interacts with the Ret receptor on the Wolffian duct to form the bud.

The Ret receptors are also at the tips of collecting ducts, so surrounding mesenchyme releasing GDNF will drive branching.

Question 7

Cause of renal agenesis

Answer 7

Ret/GDNF mutation

• > No ureteric bud OR
• > Abnormal patterning of mesenchyme

Question 8

Nephrogenesis

Answer 8

1. Collecting ducts induces the metanephric mesenchyme to differentiate into metanephric vesicles (M-E conversion)
2. These vesicles give rise to S-shaped renal tubules
3. S-shaped renal tubules differentiate into the connecting tubule, the distal convoluted tubule, loop of Henle, proximal convoluted tubule, and Bowman’s capsule.

Question 9

The epithelial/drainage portion of the kidney originates from the ___.

The filtering part of the kidney originates from the ___.

Answer 9

Epithelial/drainage portion from the ureteric bud

Filtering part from the metanephric mesenchyme

Question 10

What signaling factor is crucial for ureteric bud branching?

What signaling factor is crucial for nephrogenesis?

Answer 10

GDNF/Ret pathway for ureteric bud branching

Wnt is released from mesenchyme that convert it to epithelium in nephrogenesis

Question 11

Pax 2 is required for

Answer 11

Mesenchymal to epithelial transitions induced by ureteric bud

Question 12

Wilm’s tumors (nephroblastoma) - what happened in development?

Answer 12

Caused by WT1 gene mutations

Question 13

Posterior urethral valves

Answer 13

Can obstruct or block the outflow of urine through the urethra. When this occurs, the bladder, ureters and kidneys become progressively dilated, which can lead to damage.

Question 14

How does a horseshoe kidney form?

Answer 14

Kidneys have to ascend from the pelvis to the posterio abdominal wall in development, but if the inferior poles of two kidneys fuse, they stop at the inferior mesenteric artery –> horseshoe kidney