Question

What is the rennin-angeotensin system & what are the steps that stimulates the kidneys to produce Rennin?

Answer 1

Renin angiotensin system maintains pressure, electrolyte and blood homeostatis in the body. Renin is a protein secreted by kidney which converts angiotensinogen into angiotension and exerts pressor effect.

There are two types of renin angiotensin system -

Extrinsic RAS - it is found in blood vessels where the angiotensinogen is converted to the angiotensin on the surface of their wall.

Intrinsic RAS - it includes heart, blood vessels, kidneys and adrenals. They can synthesize all the components of this system.

Steps that stimulate kidneys to produce renin -

1) fall in blood pressure, increase ionic losses, renal ischemia and decreased blood volume acts as stimulus.

2) this changes are detected by macula densa cells and glomerular afferent pressure is reduced along with enhanced sympathetic activity.

3) This stimulates kidney (juxtaglomerular apparatus) to release renin which is activated in inactive form called protein which is later activated into renin.

4) Renin released from the kidney acts on angiotensinogen ( alpha-2 globulin) and converts it into angiotension I.

5) Angiotensin I is further converted to angiotension II by the action of angiotensin converting enzyme.

Angiotensin II acts on blood vessels and results into vasoconstriction of blood vessels which increases blood pressure.

It also increased sodium and water retention reducing ionic losses and increasing blood volume.

It causes release of aldosterone which increases sodium and water retention thus increasing blood volume.

6) Angiotension II us further converted to angiotensin III and IV by the action of aminopeptidases and finally to inactive fragments by the action of angiotensinases.