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Angiotensin I may have some minor activity, but angiotensin II is the major bio-active product. Angiotensin II has a variety of effects on the body:
* Throughout the body, angiotensin II is a potent [[vasoconstrictor]] of [[arteriole]]s.
* In the kidneys, angiotensin II constricts [[Glomerulus (kidney)|glomerular]] arterioles, having a greater effect on [[efferent arterioles]] than afferent. As with most other capillary beds in the body, the constriction of [[afferent arterioles]] increases the arteriolar resistance, raising [[systemic circulation|systemic]] [[arterial blood pressure]] and decreasing the blood flow. However, the kidneys must continue to filter enough blood despite this drop in blood flow, necessitating mechanisms to keep glomerular blood pressure up. To do this, angiotensin II constricts efferent arterioles, which forces blood to build up in the glomerulus, increasing glomerular pressure. The [[glomerular filtration rate]] (GFR) is thus maintained, and blood filtration can continue despite lowered overall kidney blood flow. Because the filtration fraction, which is the ratio of the glomerular filtration rate (GFR) to the renal plasma flow (RPF), has increased, there is less plasma fluid in the downstream peritubular capillaries. This in turn leads to a decreased [[hydrostatic pressure]] and increased [[oncotic pressure]] (due to unfiltered [[plasma proteins]]) in the peritubular capillaries. The effect of decreased hydrostatic pressure and increased oncotic pressure in the peritubular capillaries will facilitate increased reabsorption of tubular fluid.
* Angiotensin II decreases medullary blood flow through the [[Straight arterioles of kidney|vasa recta]]. This decreases the washout of NaCl and [[urea]] in the kidney [[Renal medulla|medullary space]]. Thus, higher concentrations of NaCl and urea in the medulla facilitate increased absorption of tubular fluid. Furthermore, increased reabsorption of fluid into the medulla will increase passive reabsorption of sodium along the thick ascending limb of the [[Loop of Henle]].
* Angiotensin II stimulates {{chem|Na|+}}/{{chem|H|+}} exchangers located on the apical membranes (faces the tubular lumen) of cells in the proximal tubule and thick ascending limb of the loop of Henle in addition to {{chem|Na|+}} channels in the collecting ducts. This will ultimately lead to increased sodium reabsorption.
* Angiotensin II stimulates the hypertrophy of renal tubule cells, leading to further sodium reabsorption.
* In the [[adrenal cortex]], angiotensin II acts to cause the release of [[aldosterone]]. Aldosterone acts on the tubules (e.g., the [[distal convoluted tubule]]s and the [[renal cortex|cortical]] [[collecting duct]]s) in the kidneys, causing them to reabsorb more [[sodium]] and water from the urine. This increases blood volume and, therefore, increases blood pressure. In exchange for the reabsorbing of sodium to blood, [[potassium]] is secreted into the tubules, becomes part of urine and is excreted.
* Angiotensin II causes the release of anti-diuretic hormone (ADH), also called [[vasopressin]] – ADH is made in the hypothalamus and released from the posterior [[pituitary gland]]. As its name suggests, it also exhibits vaso-constrictive properties, but its main course of action is to stimulate reabsorption of water in the kidneys. ADH also acts on the [[central nervous system]] to increase an individual's appetite for salt, and to stimulate the sensation of [[thirst]].

Translations:Renin–angiotensin system/10/en - Revision history

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