How do kidneys regulate blood pH?

Kidneys regulate blood pH by excreting hydrogen ions and reabsorbing bicarbonate ions from urine.

The kidneys play a crucial role in maintaining the body's acid-base balance, which is essential for normal cellular functions. This is achieved through a process known as renal regulation. The kidneys have the ability to adjust the body's pH by selectively excreting hydrogen ions (H+) into the urine and reabsorbing bicarbonate ions (HCO3-) back into the blood. This process is vital in preventing acidosis or alkalosis, conditions that arise from an imbalance in the body's pH.

The kidneys perform this function through two main mechanisms: the filtration of blood and the reabsorption of bicarbonate ions. In the filtration process, the kidneys filter out excess hydrogen ions from the blood. These ions are then combined with urinary buffers, primarily phosphate ions (PO4^3-) and ammonia (NH3), to form weak acids which are excreted in the urine. This process helps to remove excess acid from the body, thus raising the blood pH.

On the other hand, the kidneys also reabsorb bicarbonate ions from the urine. Bicarbonate is an important buffer in the blood, which can neutralise excess hydrogen ions, thus reducing the acidity of the blood. The reabsorption of bicarbonate ions occurs in the renal tubules, where they are transported back into the blood, contributing to the alkalinity of the blood and thus lowering the blood pH.

In summary, the kidneys regulate blood pH by excreting hydrogen ions and reabsorbing bicarbonate ions from the urine. This dual action not only removes excess acid from the body but also replenishes the blood's buffering capacity, ensuring that the body's pH remains within the normal range. This is a complex process that involves multiple steps and is regulated by various factors, including the body's overall acid-base balance, the concentration of electrolytes in the blood, and the functioning of the renal system.