Bicarbonate is lost during which of the following clinical conditions?
A. Diarrhea
B. Diuresis
C. Diaphoresis
D. Vomiting
Correct Answer: A. Diarrhea
Bicarbonate is lost in diarrhea because the lower intestinal tract contains fluids rich in bicarbonate. In pathologies with profuse watery diarrhea, bicarbonate within the intestines is lost through the stool due to increased motility of the gut. This leads to further secretion of bicarbonate from the pancreas and intestinal mucosa, leading to net acidification of the blood from bicarbonate loss.
Option B: Metabolic alkalosis occurs when a large volume of sodium-rich, bicarbonate low fluid is lost from the body. This occurs with diuretic use, cystic fibrosis, congenital chloride diarrhea, among others. The net concentration of bicarbonate increases as a result.
Option C: The sweat duct also reabsorbs bicarbonate, either directly or through hydrogen ion secretion, but the specific mechanism is unknown. The activity of Na-K-ATPase is influenced by the hormonal control of aldosterone. Overall the rate of Na, Cl, and bicarbonate reabsorption is also flow-dependent, such that higher sweating rates are associated with proportionally lower reabsorption rates resulting in higher final sweat electrolyte concentrations
Option D: Although vomiting induces gastric losses of acidic ions, there was no difference in serum bicarbonate concentrations between patients with and without vomiting. It is therefore likely that the reduction in serum bicarbonate concentration represents a true metabolic acidosis.
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