Which of the following is a cause of metabolic alkalosis?

Metabolic alkalosis is characterized by an increase in bicarbonate levels or a loss of hydrogen ions, leading to an increased pH in the blood. Vomiting is a common cause of metabolic alkalosis because it can result in the loss of gastric acid, which contains hydrochloric acid (HCl). When this acid is lost, there is a relative excess of bicarbonate in the body, leading to alkalosis.

This condition often occurs when a person experiences a significant amount of vomiting, leading to not only a depletion of stomach acids but also to a compensatory increase in bicarbonate due to the body's attempts to maintain pH balance. The loss of hydrogen ions shifts the acid-base balance towards alkalinity.

In contrast, excessive exercise primarily leads to metabolic acidosis due to increased lactic acid production. Diarrhea causes a loss of bicarbonate, which would result in metabolic acidosis, rather than alkalosis. Respiratory failure typically results in respiratory acidosis, characterized by an accumulation of carbon dioxide leading to acidosis, rather than the conditions related to metabolic alkalosis.