Q.Juxta Glomerular cells of kidneys secrete hormone:

Picture a thermostat on a heating system. It quietly senses the temperature and, whenever the room drifts too cool, it switches the heater on until things are comfortable again. The kidney has its own built-in thermostat of sorts, a small but sensitive control point called the juxtaglomerular apparatus, and its job is to keep the rate of filtration from falling too low.

The juxtaglomerular apparatus, often shortened to JGA, is a specialised region that forms at the spot where the distal convoluted tubule comes into contact with the afferent arteriole, the small vessel that brings blood into the glomerulus. Where they touch, the cells become modified into a sensitive, watchful structure. Its purpose is to help regulate the glomerular filtration rate, the amount of filtrate the kidneys produce each minute.

Here is how it acts. If the glomerular filtration rate drops, or if glomerular blood flow or blood pressure falls, the JG cells respond by releasing a substance called renin. Renin sets off a chain of events that raises the blood pressure in the glomerulus and so brings the filtration rate back up towards normal. In more detail, renin converts angiotensinogen in the blood into angiotensin I, which is then changed into angiotensin II, a powerful vasoconstrictor that raises glomerular pressure and also prompts the adrenal cortex to release aldosterone, which in turn increases the reabsorption of sodium and water. …