Question

Which of the following are the modified smooth muscles of the afferent arteriole?

• A. Juxtaglomerular cells
• B. Vasa recta
• C. Glomerulus
• D. Peritubular network

Hint:

Afferent arteriole → Juxtaglomerular cells → Renin secretion.

Answer 1

The Correct Option is A

This question is really asking which structure secretes renin, and what kind of cell is it. Let's work backward from the hormone.

1. Juxtaglomerular cells: these sit in the wall of the afferent arteriole and are smooth muscle cells that have changed shape to store and release renin. Renin is the trigger for the renin-angiotensin-aldosterone pathway that raises blood pressure, so this matches a modified smooth muscle cell exactly.
2. Vasa recta: this is a set of long capillaries running next to the loop of Henle. Capillaries are made of endothelium, not smooth muscle, so this cannot be the answer.
3. Glomerulus: this is a tuft of capillaries inside the Bowman's capsule used for filtration. Again, this is capillary tissue, not modified smooth muscle.
4. Peritubular network: this is another capillary bed that surrounds the tubules for reabsorption and secretion. It is not made of smooth muscle either.

Only the juxtaglomerular cells fit both conditions: they sit in the afferent arteriole wall and they are smooth muscle cells that have taken on a secretory job.

Let's summarize:

• Juxtaglomerular cells are modified smooth muscle in the afferent arteriole wall that release renin.
• Vasa recta, glomerulus, and peritubular network are all capillary structures, not smooth muscle.

So the correct choice is juxtaglomerular cells, option (1).