How does the kidney contribute to acid-base balance in the body?

The kidneys maintain acid-base balance by excreting hydrogen ions and reabsorbing bicarbonate from urine.

The kidneys play a crucial role in maintaining the acid-base balance in the body, which is essential for normal cellular functions. This balance is primarily maintained by the kidneys through two key processes: the excretion of hydrogen ions and the reabsorption of bicarbonate ions from the urine.

The kidneys have millions of tiny filtration units called nephrons. Each nephron contains a glomerulus and a tubule. The glomerulus filters the blood, and the filtered fluid then passes through the tubule. As the fluid travels along the tubule, the kidneys perform their crucial role in acid-base balance.

The first process involves the excretion of hydrogen ions. The cells lining the tubules can secrete hydrogen ions into the tubular fluid. This process is vital because hydrogen ions are acidic, and their excretion helps to reduce the acidity of the blood. The amount of hydrogen ions that the kidneys excrete can vary, depending on the body's needs. If the blood is too acidic, the kidneys can excrete more hydrogen ions to help restore the balance.

The second process involves the reabsorption of bicarbonate ions. Bicarbonate is an alkaline substance, and its reabsorption helps to increase the alkalinity of the blood, counteracting any excess acidity. The bicarbonate ions are reabsorbed from the tubular fluid back into the blood. Like the excretion of hydrogen ions, the amount of bicarbonate that the kidneys reabsorb can also vary. If the blood is too alkaline, the kidneys can reabsorb less bicarbonate to help restore the balance.

In addition to these two processes, the kidneys also produce a substance called ammonia. Ammonia is a weak base, and its production can help to neutralise any excess acid in the blood. The kidneys can adjust the amount of ammonia they produce, depending on the body's needs.

In summary, the kidneys maintain the acid-base balance in the body by excreting hydrogen ions, reabsorbing bicarbonate ions, and producing ammonia. These processes help to ensure that the blood maintains a stable pH, which is essential for the normal functioning of the body's cells.