What is the role played by renin - angiotensin in the regulation of kidney function?

Explanation

Renin is released from the Juxta-Glomerular Apparatus (JGA) on activation by fall in the glomerular blood pressure/flow. Renin converts angiotensinogen in blood to angiotensin I and further to angiotensin II. Angiotensin II, being a powerful vasoconstrictor, increases the glomerular blood pressure and thereby Glomerular Filteration Rate (GFR).
Angiotensin II also activates the adrenal cortex to release aldosterone. Aldosterone causes reabsorption of `Na^(+)` and water from the distal parts of the tubule. This also, leads to an increase in blood pressure and GFR. This complex mechanism is generally known as Renin Angiotensin Aldosterone System of RAAS.