How does the kidney help regulate blood composition?

The kidney plays a vital role in regulating blood composition, particularly through its ability to maintain the proper pH balance of the blood. Blood pH is crucial for various physiological processes and can impact enzyme activity, oxygen transport, and overall metabolic functions. The kidneys help regulate blood pH mainly through two processes: reabsorption and excretion of hydrogen ions and bicarbonate ions.

When blood pH drops (becomes more acidic), the kidneys can excrete more hydrogen ions while reabsorbing bicarbonate from urine back into the blood, thereby raising the blood pH. Conversely, if blood pH rises (becomes more alkaline), the kidneys will excrete bicarbonate and retain more hydrogen ions to lower the pH. This intricate balance helps to ensure that the blood remains within the narrow pH range necessary to support life and maintain metabolic processes effectively.

While other choices mention functions such as hormone production, toxin filtration, and water retention, these actions serve different roles in kidney function and overall body homeostasis but do not directly pertain to the regulation of blood composition in terms of pH balance.