All of these are actions of Atrial Natriuretic Peptide except:
Correct Answer: Mesangial constriction
Description: Ans. b. Mesangial constriction (Ref: Ganong 24/e p707)ANP causes mesangial relaxation leading to sodium excretion, not the mesangial constriction."ANP and BNP in the circulation act on the kidney's to increase Na+ excretion and injected CNP has a similar effect. They appear to produce this effect by dilating afferent arterioles and relaxing mesangial cells. Both of these actions increase glomerular filtration. In addition, they act on the renal tubules to inhibit Na+ reabsorption. Other actions include an increase in capillary permeability, leading to extravasation of fluid and a decline in blood pressure. In addition, they relax vascular smooth muscle in arterioles and venules. CNP has a greater dilator effect on veins than ANP and BNP. These peptides also inhibit renin secretion and counteract the pressor effects of catecholamines and angiotensin II. "-- Ganong 24/e p707Natriuretic HormonesTwo natriuretic hormones are secreted by the heart. The muscle cells in atria and, to a much lesser extent in the ventricles, contain secretory granules.Granules increase in number when NaCI intake is increased and ECF expanded, and extracts of atrial tissue cause natriuresis.Atrial Natriuretic Peptide (ANP)* Isolated from atria & brainQBrain natriuretic peptide (BNP; B-type natriuretic peptide)* Present in ventricles (mainly) & brain in humansQC-type natriuretic peptide (CNP)* Present in brain, pituitary, kidneys & vascular endothelial ceilsQActions of Natriuretic HormonesANP& BNP in the circulation act on kidneys to increase Na+ excretion and injected CNP has a similar effect. They appear to produce this effect by dilating afferent arterioles and relaxing mesangial cells. Both of these actions increase glomerular filtrationQ.In addition, they act on renal tubules to inhibit Na+ reabsorptionQOther actions include an increase in capillary permeability, leading to extravasation of fluid and a decline in blood pressure. In addition, they relax vascular smooth muscle in arterioles and venulesQ.CNP has a greater dilator effect on veins than ANP and BNP. These peptides also inhibit renin secretion and counteract the pressor effects of catecholamines & angiotensin lIQ.In the brain, ANP is present in neurons, and an ANP-containing neural pathway projects from part anteromedial of hypothalamus to areas in lower brain stem that are concerned with neural regulation of cardiovascular systemQIn general, the effects of ANP in the brain are opposite to those of angiotensin II, and ANP-containing neural circuits appear to be involved in lowering BP and promoting natriuresisQ.
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