What do the kidneys primarily do in the body?

The primary function of the kidneys is to filter waste products from the blood, which is accurately captured by the chosen answer. The kidneys play a critical role in maintaining homeostasis by removing metabolic waste, excess salts, and toxins through urine formation. This process also helps regulate electrolyte balance, blood pH, and blood pressure.

Through filtration in the nephrons, the functional units of the kidneys, blood is cleaned of impurities, and useful substances are reabsorbed as needed. This filtration mechanism ensures that the body maintains a stable internal environment, preventing the buildup of harmful substances.

In contrast, the other functions listed are not primarily associated with the kidneys. Regulating body temperature is primarily managed by the skin and circulatory system. Hormones that promote growth are mainly produced by other glands such as the pituitary gland, and storing blood for emergencies typically occurs in the spleen or liver, not the kidneys. Thus, the role of the kidneys in waste filtration is crucial for ensuring the overall health and balance of bodily functions.