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renin-angiotensin-aldosterone system
the regulation of sodium balance, fluid volume, and blood pressure in response to a drop in blood flow to the kidney. The kidney secretes renin, which then hydrolyzes a plasma globulin to release angiotensin I; that in turn is rapidly hydrolyzed to angiotensin II. The angiotensin causes widespread vasoconstriction and elevation of blood pressure consequent to greatly increased total peripheral resistance. A second effect, the increased secretion of aldosterone, results in retention of sodium and water by the kidneys and therefore increased extracellular fluid volume, cardiac output, and arterial blood pressure. The increased blood pressure increases blood flow to the kidney, which then shuts off the signal for renin release. Angiotensin II is a potent vasoconstrictor that also increases blood pressure.
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