The kidneys secrete ADH in response to dehydration.

A. The bicarbonate, phosphate, and protein: The major chemical buffer systems in the body are the bicarbonate buffer system, the phosphate buffer system, and the protein buffer system. These buffers help maintain pH balance in the blood and other fluids.

B. The urinary and digestive: The urinary and digestive systems are involved in excretion and digestion, not buffering.

C. The bicarbonate, nucleic acids, and protein: Nucleic acids are not major buffering systems in the body; the bicarbonate, phosphate, and protein systems are the primary ones.

D. The urinary and respiratory systems play roles in regulating acid-base balance through excretion and gas exchange but are not chemical buffer systems themselves.

A. It increases both Na+ and K+ secretion: Aldosterone increases sodium (Na+) reabsorption and potassium (K+) secretion, but it does not increase the secretion of both ions.

B. It causes the urine to be more diluted. Aldosterone causes the urine to be more concentrated by increasing sodium reabsorption and potassium secretion.

C. It reduces Na+ reabsorption and K+ secretion. Aldosterone actually increases sodium reabsorption and potassium secretion, not reduces them.

D. It increases Na+ reabsorption and K+ secretion. Aldosterone promotes sodium reabsorption in the kidneys and increases potassium secretion, leading to more concentrated urine.