Hormones Secreted by Kidney

Which of the following hormone is secreted by kidney?

Correct Answer: All the above

The kidney is not just an excretory organ — it is also an important endocrine organ that secretes three major hormones:

1. Renin

• Secreted by JG (Juxtaglomerular) granular cells of the afferent arteriole.
• Converts angiotensinogen → angiotensin-I → (via ACE) → angiotensin-II.
• Angiotensin-II is the most potent vasoconstrictor and also stimulates aldosterone release, thereby regulating blood pressure.
• Example: When blood pressure falls (e.g., in dehydration), renin is released and eventually causes BP to rise.

2. Erythropoietin (EPO)

• Secreted by interstitial cells of the kidney in response to hypoxia (low blood oxygen).
• Stimulates bone marrow to produce more RBCs.
• Example: Animals at high altitude (less O₂) → kidney secretes EPO → more RBCs → better oxygen carrying capacity.

3. 1,25-Dihydroxycholecalciferol (Active Vitamin D₃)

• Kidney performs the final hydroxylation step: 25-hydroxycholecalciferol → 1,25-dihydroxycholecalciferol (calcitriol) — the active form of vitamin D.
• Calcitriol promotes intestinal absorption of calcium and phosphorus.
• Deficiency → rickets in young animals, osteomalacia in adults.