Lecture 29 – Renal Physiology IV

If blood pressure or volume decreases frequency of ap

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If blood pressure or volume decreases, frequency of AP from these receptots will  increase and ADH secreton will increase Sodium Balance Main cation in ECF In all tubular segments where Na is reabsorbed, it is actively transported across  the basolateral membrane by the Na/K ATPase pump
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Because this active transport keeps the intracellular Na low, Na passively enters the cell  across the apical membrane In the PT, entry of Na into the tubular epithelial cells as carried out by transport proteins  that couple movement to movement of organic molecules (like glucose or an AA) or to  counter transport of hydrogen ions  Distal Tubule still have active transport, same mechanism in apical membrane there are many iddferent mechanisms either passively thorugh Na channels can cotrasport with chloride we have to maintain the membrane potential, whih means you need to maintain the  concentration of other cations and anions on both sides this means reabsorption has to be matched across all ions (repabosrption of opposite  charges or secretion of same charge) chloride and bicarbonate are the most abundant anions in tubular fluid, they are most  frequently reabsorbed when Na is reabsorbed Aldosterone Regulates K secretion and Na reabsorption Binds to cytosolic receptors Steroid hormone produced by the adrenal cortex, recetrs are located in the cytosol  because they can easily pass through lipid bilayer Once it binds Stimulats the opening of Na and K channels in the apicl membrane and the synthesis  and insertion of more of those channels So it stimulate a passive pathway Stimulates the snethsis and insertion of more Na/KATPase pumps in the asolateral  membrane Aldosterone Genesis Renin-angiotensin-aldosterone system Within the JGA, there are granular cells that secrete renin into the bloodstream Rennin is a proteolytic enzyme, not really a hormone Within the walls of the DT at the JGA are the macula densa cells which detect changes  in sodium and chloride as well as flow rate of the tubular fluid When Na decreases, renin secretion increases Once renin is released into the bloodstream, it converts angiotensinogen into ANgI AngI is then converted to AngII using ACE (produced by capillary endothelial cells)
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When AngII increases, there will be an incease in aldosterone secretion and increase in  sodium reabsorption in the late distal tubules and in CDs This will increase the ECF osmolarity Acts indirectly on posterior pituitary, will increase ADH secretion This increases water reabsorption Increase in volume and ultimate increaee in MAP Also stimulates other hypothalamic neurons to increase thirst – drink more water and  plasma volume goes up
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