ANATOMY

Detailed explanation-1: -The kidneys have two main ways to maintain acid-base balance-their cells reabsorb bicarbonate HCO3− from the urine back to the blood and they secrete hydrogen H+ ions into the urine. By adjusting the amounts reabsorbed and secreted, they balance the bloodstream’s pH.

Detailed explanation-2: -Through the action of carbonic anhydrase (CA) IV and II, the filtered bicarbonate gets reabsorbed back into the blood via electrogenic sodium bicarbonate cotransporter 1 (NBCe1) on the basolateral side.

Detailed explanation-3: -Second, both intracellular and extracellular buffers are used to buffer endogenous and exogenous acid loads and must be replenished to maintain acid-base homoeostasis. The kidneys produce “new bicarbonate” to do so, and the primary mechanism of new bicarbonate generation involves renal ammonia metabolism.

Detailed explanation-4: -The kidney excretes hydrogen ion through the processes of titratable acid excretion and urinary ammonium excretion1, 2). Quantitatively, urinary ammonium excretion is the primary mechanism of net acid excretion both under basal conditions and in response to acid loads1-3).

Detailed explanation-5: -It was concluded that HCO3-reabsorption in the proximal tubule was mediated by H+ secretion, but that carbonic anhydrase located in the luminal membrane of the cell prevented H2CO3 from accumulating in the tubular fluid. In the distal tubule the intratubular pH was 0.85 U lower than the equilibrium pH.