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Angiotensins
Angiotensin I is converted to the octapeptide angiotensin II by the action of angiotensin converting enzyme (ACE) which is widely present in vascular endothelium and is in particularly high concentration in lung. This is significant because the entire venous return flows through the lung providing for the rapid conversion of angiotensin I to angiotensin II which is the active form of angiotensin and has two highly important physiological actions.
Angiotensin II is a more potent vasoconstrictor than norepinephrine and plays an important role in the regulation of blood pressure. In the kidney it has a greater effect on the efferent than on the afferent arteriole thus reducing GFR less than RBF, increasing filtration fraction and altering peritubular Starling factors to favor tubular fluid reabsorption.
It acts on the zona glomerulosa of the adrenal gland to stimulate the secretion of aldosterone which is a major factor in regulation of sodium balance.
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