Renal Acid-Base Regulation Kidneys help regulate blood ph by excreting H+ and reabsorbing HCO3 Most of the h+ secretion occurs across the walls of the pct in exchange for Nat Antiport mechanism Moves Nat and H+ in opposite directions. Normal urine normally is slightly acidic because the kidneys reabsorb almost all HCO3 and excrete h+ Returns blood pH back to normal range
Renal Acid-Base Regulation ◼ Kidneys help regulate blood pH by excreting H+ and reabsorbing HC03 - . ◼ Most of the H+ secretion occurs across the walls of the PCT in exchange for Na+ . ◼ Antiport mechanism. ◼ Moves Na+ and H+ in opposite directions. ◼ Normal urine normally is slightly acidic because the kidneys reabsorb almost all HC03 - and excrete H+ . ◼ Returns blood pH back to normal range
Reabsorption of HCO3 Apical membranes of tubule cells are impermeable to HCO3 Reabsorption is indirect when urine is acidic, hco combines with h+ to form H,CO3, which is catalyzed by ca located in the apical cell membrane of PCT ximal convoluted tubule )I As [CO2]increases in the filtrate Co2 diffuses into tubule cell and forms H2 CO3 H Co dissociates to Hco and H+ HCO3 generated within tubule cell diffuses into peritubular capillary
Reabsorption of HCO3 - ◼ Apical membranes of tubule cells are impermeable to HCO3 - . ◼ Reabsorption is indirect. ◼ When urine is acidic, HCO3 - combines with H+ to form H2CO3 - , which is catalyzed by ca located in the apical cell membrane of PCT (proximal convoluted tubule) . ◼ As [CO2] increases in the filtrate, CO2 diffuses into tubule cell and forms H2CO3 . ◼ H2CO3 dissociates to HCO3 - and H+ . ◼ HCO3 - generated within tubule cell diffuses into peritubular capillary
Acidification of Urine HCO3 Na HcO ATPase K Na+H,CoxH2 0 +co,Na H Blood Na CA H2l 0+ co Na Hco+H+- -H2 CO3 HPO2比Hpo Filtration Lumen NH3-NH Proximal tubule cell
Acidification of Urine
№a++Hc0 H+H H2CO3 H*+ HCO3 CA H20+c0 HPO H2C03 NH NH4 H2PO4 CA C0,+H20
CO2 + H2O CA H2CO3 H2CO3 H + + HCO3 - HPO4 2- Na+ + HCO3 - CA H2O + CO2 H + NH3 H + NH4 + H2PO4 -
Urinary Buffers Nephron cannot produce urine at pH<45 a In order to excrete more h+, the acid must be buffered a H+ secreted into the urine tubule and combines with HPO4 2 or NH3- HPO42+H+一H2PO4 NH3+H一NH4+
Urinary Buffers ◼ Nephron cannot produce urine at pH< 4.5. ◼ In order to excrete more H+, the acid must be buffered. ◼ H+ secreted into the urine tubule and combines with HPO4 2- or NH3 . ◼ HPO4 2- + H+ H2PO4 - ◼ NH3 + H+ NH4 +