The main function of the kidneys is to filter waste products and excess substances from the bloodstream to form urine, which is then excreted from the body. They play a critical role in maintaining homeostasis by regulating electrolyte balance, blood pressure, and fluid levels. In addition to waste removal, kidneys also help control acid-base balance and produce hormones such as erythropoietin, which stimulates red blood cell production. Their efficient functioning is essential for overall health, as they contribute significantly to metabolic and fluid balance in the body.