Question

Enzyme ‘renin’ is secreted by
A. Cells of the stomach
B. Cells of the intestine
C. The cortical cells of the kidney
D. The cells of the Juxtaglomerular apparatus the of kidney

Answer 1

Hint: Renin is the primary hormone involved in the control of blood pressure and various other physiological functions.

Complete answer:
Enzyme ‘renin' is secreted by the ‘cells of the Juxtaglomerular apparatus of kidney'.
- The juxtaglomerular apparatus (JGA) plays a complex regulatory role. A fall in glomerular blood flow/ glomerular blood pressure/ glomerular filtration rate (GFR) can activate the JG cells to release renin or Angiotensinogenase.
- Renin along with Angiotensin II and Aldosterone form a hormone system within the body that is essential for the regulation of blood pressure and fluid balance. This is known as the ‘Renin Angiotensin Aldosterone System' (RAAS).

Additional Information:
1. Renin is released near the afferent arteriole from the Juxtaglomerular cells of the renal juxtaglomerular apparatus (JGA) in response to one of three factors:
- Reduced sodium delivery to the distal convoluted tubule of the kidney detected by macula densa cells.
- Reduced arterial blood pressure in the kidney detected by baroreceptors in the afferent arteriole.
- Sympathetic stimulation of the JGA.
2. The released renin converts Angiotensinogen produced from the liver into Angiotensin I.
3. Angiotensin I is further converted into Angiotensin II by the enzyme ‘Angiotensin-Converting Enzyme' released by the liver.
4. Angiotensin II, causes powerful vasoconstriction and increases the glomerular blood pressure and thereby GFR.
5 Angiotensin II has other functions also. It stimulates the adrenal cortex to release Aldosterone. Aldosterone results in the reabsorption of sodium and water from the distal parts of the tubule i.e. DCT leads to an increase in blood pressure and GFR.

So, the correct answer is ‘The cells of the Juxtaglomerular apparatus of the kidney'.

Note:
- JGA is found between the afferent arteriole and the distal convoluted tubules of the kidney. - It comprises ‘Macula densa’, ‘Juxtaglomerular cells', and ‘Mesangial cells'.
- Renin can also be referred to as a hormone, as it has a receptor, the (pro)renin receptor, also known as the renin receptor as well as enzymatic activity with which it hydrolyzes angiotensinogen to angiotensin I.
- ANF secreted by the heart antagonizes the action of renin.