What do the kidneys regulate in relation to bicarbonate?

The kidneys play a crucial role in maintaining the body's acid-base balance, and one of the primary ways they achieve this is through the regulation of bicarbonate. Bicarbonate (HCO3-) is a key component in the buffering system that helps maintain a stable pH in the blood and other bodily fluids.

When the blood is too acidic, the kidneys can reabsorb bicarbonate from the urine back into the bloodstream, which helps to neutralize excess hydrogen ions (H+) and raise the pH to a more normal level. Conversely, if the blood becomes too alkaline, the kidneys can excrete more bicarbonate to help lower the pH. This process of reabsorbing bicarbonate is vital for efficient acid-base balance and compensating for metabolic and respiratory acid-base disturbances.

The other answer choices do not accurately reflect the specific role of the kidneys in bicarbonate management. The excretion of carbon dioxide primarily involves the lungs rather than the kidneys. Synthesis of sodium is not a direct function of the kidneys; instead, they regulate sodium levels through filtration and reabsorption processes. Lastly, while the kidneys do filter electrolytes, including chloride, the regulation of bicarbonate is far more central to their function in maintaining acid-base homeostasis.