Question

Enzyme secreted by the kidneys that is involved in the control of blood pressure is :

• A. \( \text{Erythropoietin} \)
• B. \( \text{Angiotensin} \)
• C. \( \text{Aldosterone} \)
• D. \( \text{Renin} \)

Hint:

\textbf{Renal Physiology: Renin-Angiotensin-Aldosterone System (RAAS).} Understanding the RAAS is essential for comprehending the hormonal regulation of blood pressure and fluid balance by the kidneys. Renin is the key initiating enzyme in this cascade.

Answer 1

The Correct Option is D

The kidneys play a crucial role in the regulation of blood pressure through the renin-angiotensin-aldosterone system (RAAS). When blood pressure or blood volume decreases, the juxtaglomerular cells in the kidneys secrete an enzyme called renin. Renin then acts on angiotensinogen (a plasma protein produced by the liver) to convert it to angiotensin I. Angiotensin I is further converted to angiotensin II by angiotensin-converting enzyme (ACE), which is primarily found in the lungs. Angiotensin II is a potent vasoconstrictor that increases blood pressure directly and also stimulates the release of aldosterone from the adrenal cortex, leading to increased sodium and water reabsorption by the kidneys, further raising blood pressure and volume. Let's briefly look at the other options: Erythropoietin: This hormone is secreted by the kidneys in response to hypoxia and stimulates red blood cell production in the bone marrow. While it affects blood volume indirectly over time, it is not the primary enzyme involved in rapid blood pressure control. Angiotensin: This is a hormone involved in blood pressure regulation, but it is not secreted by the kidneys. Angiotensinogen is produced by the liver, and angiotensin I is a product of renin's action. Aldosterone: This is a steroid hormone produced by the adrenal cortex that increases sodium and water reabsorption in the kidneys, thus raising blood pressure. Its release is stimulated by angiotensin II and high potassium levels, but it is not secreted by the kidneys. Therefore, the enzyme secreted by the kidneys that is directly involved in the control of blood pressure through the RAAS is renin.