Which of the following identifies the amount of urine that an average adult produces per day?

a. Decrease in hydrogen ions: A decrease in hydrogen ions (H+) would indicate a condition of alkalosis, not acidosis.

b. Decrease in carbon dioxide: A decrease in carbon dioxide (CO2) usually leads to respiratory alkalosis because CO2 is acidic in nature.

c. Decrease in ketones: Ketones are acidic compounds, and their decrease is not associated with acidosis. In fact, an increase in ketones can cause ketoacidosis.

d. Decrease in bicarbonate ions: Bicarbonate (HCO3-) is a base, and a decrease in its concentration can lead to metabolic acidosis, as it reduces the buffering capacity of the blood against excess H+.

a. Secretes fluid to reduce friction between layers: This is correct. The pleural membranes secrete pleural fluid, which reduces friction between the visceral and parietal layers during breathing.

b. Secretes a substance that reduces surface tension of alveoli: This describes the function of surfactant, which is secreted by alveolar cells, not pleural membranes.

c. Secretes a substance to keep epithelial cells wet: This is a general description that doesn't specifically apply to pleural membranes.

d. Secretes fluid involved in protection from infections: While pleural fluid may have some protective roles, its primary function is to reduce friction, not directly to protect from infections.