<P> The renin--angiotensin system (RAS) or the renin--angiotensin--aldosterone system (RAAS) is a hormone system that regulates blood pressure and fluid balance . </P> <P> When renal blood flow is reduced, juxtaglomerular cells in the kidneys convert the precursor--prorenin, already present in the blood into renin and secrete it directly into the circulation . Plasma renin then carries out the conversion of angiotensinogen, released by the liver, to angiotensin I. Angiotensin I is subsequently converted to angiotensin II by the enzyme angiotensin - converting enzyme (ACE) found in the lungs . Angiotensin II is a potent vasoconstrictive peptide that causes blood vessels to narrow, resulting in increased blood pressure . Angiotensin II also stimulates the secretion of the hormone aldosterone from the adrenal cortex . Aldosterone causes the renal tubules to increase the reabsorption of sodium and water into the blood, while at the same time causing the excretion of potassium (to maintain electrolyte balance). This increases the volume of extracellular fluid in the body, which also increases blood pressure . </P>

What is the purpose of the renin angiotensin aldosterone system
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