Question

What is the signal that activates the RAAS pathway?

Answer 1

The primary stimulus to activation of the renin-angiotensin-aldosterone system is the lowered blood pressure. (less than or equal to 100mm of Hg).

Due to fall in blood pressure kidneys release the enzyme Rennin in the bloodstream.

Then Rennin splits angiotensinogen (Enzyme in the liver) into angiotensin I.

Angiotensin I [ inactive] is now cleaved by angiotensin converting enzyme (ACE), present in the lungs. Converting it to the more active molecule i.e. angiotensin II .

Angiotensinogen is a hormone, causes the Arterioles to constrict, increasing blood pressure.

Angiotensin II also stimulates the release of the hormone aldosterone from the adrenal glands which are located above kidneys.

Aldosterone results in the Sodium reservation and excretion of potassium. The sodium causes water retention thereby increasing blood volume and blood pressure.