The Juxtaglomerular (JG) apparatus has a regulatory role to play.

When there is a fall in glomerular filtration rate (GFR), they activate the JG cells to release renin which gets converted to angiotensinogen in blood to angiotensin I and further to angiotensin II. Angiotensin II, is a powerful vasoconstrictor that increases the GFR.

Angiotensin II is also responsible for activating the adrenal cortex to release Aldosterone which causes reabsorption of Na+ and water from the distal parts of the tubule leading to an increase in blood pressure and GFR.

This mechanism is known as the Renin-Angiotensin mechanism that regulates the kidney function.

The juxtaglomerular apparatus is a structure formed by the distal convoluted tubule and the glomerular afferent arteriole.