Regulation of Acid–Base Balance
A patient excretes 2 L of urine at a pH of 7.4. The urine bicarbonate concentration is 5 mEq/L. What is the titratable acid excretion?
b. It is negative 10 mEq.
d. Cannot determine without data for ammonium.
(c) The urine is already neutral; thus, it contains no acidity that can be titrated.
Which of the following is an acid load per se or becomes an acid load after metabolism?
b. Eating unsweetened grapefruit juice
c. Eating sweetened grapefruit juice
d. Intravenous infusion of sodium lactate
(a) Animal protein, when metabolized, adds acid to the body. The other substances, when metabolized, generate bicarbonate and thus become an alkali load.
How does the proximal tubule handle filtered bicarbonate?
a. Bicarbonate is taken up by the tubular cells on a symporter with sodium.
b. Bicarbonate is taken up by the tubular cells via antiport with small base anions (eg, formate).
c. Bicarbonate is taken up by the tubular cells via antiport with chloride.
d. Bicarbonate combines with a proton in the lumen and is converted to carbon dioxide and water.
(d) Filtered bicarbonate combines with protons to become carbon dioxide and water. Simultaneously, it is generated within the tubular cells and exported with sodium across the basolateral membrane.
In which situation(s) would you expect to see decreased or no renal excretion of acid equivalents?
a. During a major metabolic acidosis such as diabetic ketoacidosis.
b. During a time when the pancreas is secreting a high amount of bicarbonate-rich fluid into the GI tract.
c. In response to consuming a large number of antacid tablets.
d. All of these situations.
(c) Antacid tablets constitute an alkali load that reduce or even exceed metabolic acid production.
What is the fate of ammonium secreted in the proximal tubule?