Renin Secreting Cells of Kidney

Renin is secreted by which cells of the kidney?

Correct Answer: JG granular cells of kidney

Renin is a proteolytic enzyme secreted by the Juxtaglomerular (JG) granular cells, which are specialized smooth muscle cells of the afferent arteriole in the kidney.

Renin-Angiotensin-Aldosterone System (RAAS)

• Renin (kidney) → converts Angiotensinogen to Angiotensin I
• ACE (Angiotensin Converting Enzyme, lungs) → converts Angiotensin I to Angiotensin II
• Angiotensin II → stimulates Aldosterone secretion from adrenal cortex
• Aldosterone → increases Na⁺ reabsorption and K⁺ secretion in collecting tubules

Important Distinction: Renin vs. Rennin

• Renin: Secreted by JG granular cells of kidney; converts Angiotensinogen to Angiotensin-I.
• Rennin (Chymosin): Secreted by gastric chief cells (stomach); a protein-digesting enzyme that curdles milk by transforming caseinogen into insoluble casein. Important in cheese making.

JG Apparatus Composition

• Macula densa cells (DCT) — detect Na⁺ concentration
• JG granular cells (afferent arteriole) — secrete renin
• Extraglomerular mesangial cells (Lacis cells)