Answer to Question #129126 in Zoology for vathsalya

Question

mechansim of ANP counter checks

Answer 1

 Mechanism of ANP counterchecks

 The Atrial natriuretic peptide, or ANP, is a natriuretic peptide hormone secreted from the cardiac atria that in humans is encoded by the gene called NPPA . ANP is synthesized and secreted in the atrial walls by the walls of cardiac muscle.These cells have receptors which respond to increased stretching of the atrial wall due to increase atrial blood volume.. The main function of ANP is causing a reduction in expanded extracellular fluid (ECF) volume by increasing renal sodium excretion. It acts acutely to reduce plasma volume by three  mechanisms: by increasing renal excretion of salt and water, vasodilation, and increasing vascular permeability.  ANP acts on the kidney to increase sodium and water excretion (natriuresis) in the following ways:

·      ANP effects sodium channels at both the apical and basolateral sides of the medullary collecting ducts. ANP inhibits ENaC on the apical side and the Sodium Potassium ATPase pump on the basolateral side in a cGMP PKG dependent manner resulting in less sodium re-absorption and more sodium excretion.

·      ANP increases glomerular filtration rate and glomerular permeability. ANP directly dilates the afferent arteriole and counteracts the norepinephrine induced vasoconstriction of the afferent arteriole.  Some studies suggest that ANP also constricts the efferent arteriole, but this is not a unanimous finding.  ANP inhibits the effect of Angiotensin II on the mesangial cells, thereby relaxing them. ANP increases the radius and number of glomerular pores, thereby increasing glomerular permeability and resulting in greater filter load of sodium and water.

·      Increases blood flow through the vasa recta, which will wash the solutes (sodium chloride (NaCl), and urea) out of the medullary interstitium. The lower osmolarity of the medullary interstitium leads to less reabsorption of tubular fluid and increased excretion.