It’s difficult for me to remember all the steps of RAAS, or the Renin-Angiotensin-Aldosterone System. But this cute little diagram (snatched from Wikipedia) serves as a spiffy reminder.
But what’s the point of “RAAS”? Two important things: blood volume and blood pressure regulation.
When blood pressure begins to drop, the kidneys detect this and decide to initiate a defense mechanism—the release/secretion of an enzyme called renin. This special enzyme then floats around the blood and converts inactive angiotensinogen (a precursor peptide in the blood) into angiotensin I. Angiotensin I is a protein in the blood that causes blood vessels to constrict… but only to a minimal extent. For a more profound effect, angiotensin I is sent to the lungs, the home of an enzyme named ACE (Angiotensin Converting Enzyme). Angiotensin II is the product—a stronger hormone that can deliver more powerful changes in blood pressure (namely, an elevation in blood pressure). Angiotensin II can work directly on the blood vessels to cause blood pressure increases through vasoconstriction (essentially, forcing the diameter of the blood vessels to shrink so the blood inside will create more friction against the wall of the vessel, which increases blood pressure). But something even more amazing that angiotensin II can do is stimulate the release of aldosterone. How does it do this? By going over to the adrenal cortex (a part of the adrenal endocrine glands that sit comfortably above the kidneys like a Santa Claus hat) and stimulating the release of aldosterone, a hormone.
So what does aldosterone do?? It goes to the kidney and says, “You have to reabsorb sodium and water and release potassium. This way, blood volume goes up again!”
And so, your body’s blood pressure and blood volume is under control again… All thanks to RAAS!