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Regulation of Acid–Base Balance

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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?

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a. It is 10 mEq.

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b. It is negative 10 mEq.

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c. It is zero.

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d. Cannot determine without data for ammonium.

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(c) The urine is already neutral; thus, it contains no acidity that can be titrated.

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Which of the following is an acid load per se or becomes an acid load after metabolism?

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a. Eating a large steak

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b. Eating unsweetened grapefruit juice

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c. Eating sweetened grapefruit juice

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d. Intravenous infusion of sodium lactate

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(a) Animal protein, when metabolized, adds acid to the body. The other substances, when metabolized, generate bicarbonate and thus become an alkali load.

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How does the proximal tubule handle filtered bicarbonate?

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a. Bicarbonate is taken up by the tubular cells on a symporter with sodium.

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b. Bicarbonate is taken up by the tubular cells via antiport with small base anions (eg, formate).

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c. Bicarbonate is taken up by the tubular cells via antiport with chloride.

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d. Bicarbonate combines with a proton in the lumen and is converted to carbon dioxide and water.

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(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.

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In which situation(s) would you expect to see decreased or no renal excretion of acid equivalents?

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a. During a major metabolic acidosis such as diabetic ketoacidosis.

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b. During a time when the pancreas is secreting a high amount of bicarbonate-rich fluid into the GI tract.

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c. In response to consuming a large number of antacid tablets.

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d. All of these situations.

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(c) Antacid tablets constitute an alkali load that reduce or even exceed metabolic acid production.

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What is the fate of ammonium secreted in the proximal tubule?

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a. It flows ...

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