Question

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

Answer 1

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, increase the glomerular blood pressure and thereby Glomerular Filteration Rate (GFR).
Angiotensin II also activates the adrenal cortex to release aldosterone. Aldosterone causes reabsorption of $N{a}^{+}$ and water from the distal parts fo the tubule. This also leads to an increase in blood pressure and GFR. This complex mechanism is generally known as renin angiotensin aldosterone system or RAAS.