How stimulation of Renin-Angiotensin system restores plasma volume.

The Renin-Angiotensin System (RAS) or the Renin-Angiotensin-Aldosterone System (RAAS) is a hormone system that regulates blood pressure and fluid balance. 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 converts angiotensinogen, released by the liver to angiotensin I. Angiotensin I is subsequently converted to angiotensin II by the angiotensin converting enzyme (ACE). 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, simultaneously causing the excretion of potassium (to maintain electrolyte balance). This increases the volume of extracellular fluid in the body which also increases blood pressure.