Question

Juxta-glomerular cells form
A. Angiotensinogen and angiotensin
B. Renin and Erythropoietin
C. Counter-current
D. Selective secretory and absorptive apparatus

Answer 1

Hint: It is a proteolytic enzyme whose name resembles one of the enzymes of digestive juices. This digestive enzyme is found in the stomach of infants.

Complete Answer:
The Juxta-glomerular apparatus is a specialized structure made by a combination of the distal convoluted tubule and the glomerular afferent arteriole. Juxta-glomerular apparatus is located at the vascular pole where the afferent and efferent arterioles enter and leave the glomerulus. It is composed of three types of cells:
1. Juxta-glomerular cell (JG cells)
2. Macula Densa cells
3. Mesangial cells

1. Juxta-glomerular cells: Before entering the glomerulus, the afferent arterioles show a thickening of its wall. This thickening contains modified smooth muscle cells called Juxta-glomerular cells.
- Juxta-glomerular cells synthesize, store and release a proteolytic enzyme called Renin. Renin is stored in granules of the Juxta-glomerular cells. The Juxta-glomerular cells when stimulated release renin. These Juxta-glomerular cells are stimulated when the blood pressure in the arteriole falls. The secretion of Renin into the bloodstream increases blood pressure via the renin-angiotensin-aldosterone system.
- Juxta-glomerular cells also secrete erythropoietin which increases the production of RBCs (erythropoiesis). The secretion of erythropoietin is triggered when the kidney receives blood with low oxygen levels.
- When renin is released into the blood, it acts on a specific plasma protein called angiotensinogen. Angiotensinogen is secreted by the liver. By the activity of renin, the angiotensinogen is converted into angiotensin I.
- Angiotensin I is converted into angiotensin II by the activity of the angiotensin-converting enzyme (ACE) secreted from the lungs. Angiotensin I and Angiotensin II are collectively called Angiotensin.
- The counter-current mechanism helps in the concentration of urine.
- Selective secretory and absorptive apparatus are the tubules (PCT and DCT). Tubular reabsorption is the process by which water and other substances are transported from renal tubules back to the blood. Tubular secretion is the process by which the substances are transported from the blood into renal tubules.

So, the correct answer is B. Juxta-glomerular cells form Renin and Erythropoietin.

Note: Juxta-glomerular cells have baroreceptors (receptors that detect the change in pressure) which get stimulated by the fluctuation of blood pressure. As baroreceptors sense the fall in blood pressure Renin is released.