What is the significance of juxtaglomerular apparatus (JGA) in kidney function?

Explanation

When glomerular filtration pressure decreases then JGA cells secrete an enzyme Renin which activates angiotensinogen of blood plasma to angiotension-I which changes into angiotensin-II which stimulates adrenal cortex to secrete aldosterone hormone.
Aldosterone causes increased reabsorption of `Na_(+)` and water from the nephric filtrate into interstitial fluid from the distal parts of renal tubule. This increases the blood pressure and GFR. This mechanism is called Renin-Angiotensin mechanism.