ROLE OF KIDNEYS IN ACID-BASE BALANCE QUESTIONS WITH COMPLETE SOLUTIONS

load of fixed acid (protons) generated as a result of metabolism in an individual on a typical western diet correct answer: approximately 1 mmol of protons per kg body weight per day 2 major components of the body's major buffering system: correct answer: CO2 and HCO3- kidneys vs lungs correct answer: - Whereas the lungs excrete the large amount of CO2 formed by metabolism, the kidneys are crucial for excreting nonvolatile acids. - The kidneys play a critical role in helping the body rid itself of excess acid that accompanies the intake of food or that forms in certain metabolic reactions. - By far, the largest potential source of acid is CO2 production, which occurs during oxidation of carbohydrates, fats, and most amino acids the lungs excrete this prodigious amount of CO2 by diffusion across the alveolar-capillary barrier, preventing the CO2 from forming H+ . - However, metabolism also generates nonvolatile acids —such as sulfuric acid, phosphoric acid, and various organic acids—that the lungs cannot handle. - In addition, metabolism generates nonvolatile bases, which end up as HCO3-. - Subtracting the metabolically generated base from the metabolically generated acid leaves a net endogenous H+ production of ~40 mmol/day for a person weighing 70 kg. - The strong acids contained in a typical Western acid-ash diet (20 mmol/day of H+ gained) and the obligatory loss of bases in stool (10 mmol/day of OH− lost) represent an additional acid load to the body of 30 mmol/day. - Thus, the body is faced with a total load of nonvolatile acids (i.e., not CO2 ) of ~70 mmol/day—or ~1 mmol/kg body weight—derived from metabolism, diet, and intestinal losses. - The kidneys handle this acid load by "dividing" 70 mmol/day of carbonic acid (H2 CO3): excreting ~70 mmol/day of H + into the urine and simultaneously transporting 70 mmol/day of new HCO3- into the blood.