Question

What is the function of renin secreted by juxtaglomerular (JG) cells?

• A. Increase blood pressure
• B. Increase blood volume
• C. Decrease blood volume
• D. A and B

Hint:

Renin activates RAAS. The ultimate effects are increased blood pressure, increased sodium retention, increased water retention, and increased blood volume.

Answer 1

The Correct Option is D

Concept: Renin is an enzyme released by juxtaglomerular cells when blood pressure or blood volume decreases. It initiates the renin-angiotensin-aldosterone system (RAAS), which helps restore circulatory homeostasis.

Step 1: Release of Renin
When blood pressure falls, JG cells detect the change and secrete renin into the bloodstream.

Step 2: Formation of Angiotensin II
Renin converts angiotensinogen into angiotensin I. Angiotensin I is subsequently converted into angiotensin II. Angiotensin II is a powerful vasoconstrictor.

Step 3: Increase in Blood Pressure
Vasoconstriction narrows blood vessels, thereby increasing blood pressure. Thus, renin indirectly causes an increase in blood pressure.

Step 4: Increase in Blood Volume
Angiotensin II stimulates secretion of aldosterone from the adrenal cortex. Aldosterone enhances sodium and water reabsorption in the kidneys. As a result, blood volume increases.

Step 5: Evaluate the Options
Option (A) is correct because blood pressure increases. Option (B) is correct because blood volume increases. Option (C) is incorrect because blood volume does not decrease. Therefore, the best answer is Option (D). \[ \boxed{\text{(D) A and B}} \]