Question

Angiotensinogen is a protein produced and secreted by –
A. Juxtaglomerular (JG) cells
B. Macula densa cells
C. Endothelial cells (cells lining the blood vessels)
D. Liver cells

Answer 1

Hint: An α-2-globulin that synthesizes and secretes mainly by the liver cells and is also known as renin substrate.

Complete answer:
Angiotensinogen is cleaved at the N-terminus to release 10 amino acids by renin that resulted in angiotensin I, which finally modified to become angiotensin II. Renin is an enzyme that is synthesized by juxtaglomerular cells of the renal cortex. It cleaves angiotensinogen between the leucine and valine to create the decapeptide, angiotensin I.

Mechanism of renin- angiotensin:
- The renin-angiotensin system is essential for the regulation of blood pressure, homeostasis of water, and sodium through actions of angiotensin II.
- When glomerular blood pressure decreases in the kidney, it activates the juxtaglomerular cells (JG cells) to release renin.
- This renin converts the angiotensinogen in the blood to angiotensin I and finally to angiotensin II. This angiotensin II is a powerful vasoconstrictor that increases the glomerular blood pressure and also increases the glomerular filtrate rate.
- At the same time, angiotensin II also stimulates the adrenal cortex to release Aldosterone. This aldosterone reabsorbs the Na+ and water from the distal parts of the tubule.
- Aldosterone also increases the blood pressure and glomerular filtrate rate.

So, the correct answer is ‘liver cells.

Note: Atrial Natriuretic Factor (ANF) inhibits renin secretion, which further inhibited the production of angiotensin and aldosterone. This Atrial Natriuretic Factor is mainly responsible for the vasodilation and thereby decreases the blood pressure in vessels.