Which organ is primarily responsible for maintaining salt and water balance in the body?

The kidneys play a crucial role in maintaining salt and water balance in the body through a process called renal regulation. They filter blood to remove waste products and excess substances, including salts and water, which helps to regulate the volume of fluid in the bloodstream and maintain a proper electrolyte balance.

The kidneys achieve this through complex mechanisms including filtration, reabsorption, and secretion within specialized structures called nephrons. When the body requires more water retention due to dehydration, for example, the kidneys adjust by reabsorbing more water back into the bloodstream and excreting a more concentrated urine. Conversely, when there is excess water, the kidneys allow more water to be excreted, thus diluting the urine.

In contrast, while the liver, pancreas, and spleen have important functions within the body, they do not have a direct role in the regulation of salt and water balance. The liver is primarily involved in detoxification and metabolism, the pancreas in insulin production and digestion, and the spleen in immune function and blood filtration.