All of the following statements about angiotensin II are TRUE, EXCEPT:
Correct Answer: Secreted from endothelium
Description: Angiotensinogen is the circulating protein substrate from which renin cleaves angiotensin I. It is synthesized in the liver within a few seconds to minutes after formation of angiotensin I, two additional amino acid are split from the angiotensin I to from the 8-amino acid peptide angiotensin II. This conversation occurs almost entirely in the lungs while the blood flows through the small vessels of lungs, catalyzed by an enzyme called angiotensin conveing enzyme (ACE) that is present in the endothelium of the lungs vessels. FUNCTION: Angiotensin II is an extremely powerful vasoconstrictor. Vasoconstrictor occurs intensely in the aerioles and much less so in the veins. It decrease excretion of both slowly salt and water by the kidneys. This slowly increases the extracellular fluid volume, which then increase the aerial pressure during subsequent hours and days. It exes impoant actions at vascular smooth muscle, adrenal coex, kidney, hea and brain. Act directly on the zona glomerulosa of the adrenal coex to stimulate aldosterone biosynthesis. At higher concentrations, angiotensin II also stimulates glucocoicoid biosynthesis. Angiotensin II act on the kidney to cause renal vasoconstriction, contraction of mesangial cells with a resultant decrease in GFR increase proximal tubular sodium reabsorption, and inhibit the secretion of renin. In addition to its central effects on blood pressure, angiotensin II acts on the central nervous system to stimulate drinking (dipsogenic effect ) and increase the secretion of vasopressin and adrenocoicotropic hormone (ACTH). Ref: Ganong 23/e, page 670 ; Guyton 11/e, page 201-02,223-24,907
Category:
Physiology
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