What is the primary function of the kidneys?

The primary function of the kidneys is to filter waste products and excess substances from the blood, which are then excreted as urine. This vital role helps maintain homeostasis, regulating the body's fluid balance, electrolyte levels, and pH, while also eliminating potentially harmful waste materials resulting from metabolism.

While the kidneys do indeed produce certain hormones, such as erythropoietin and renin, their fundamental role in waste filtration is paramount. Regulation of body temperature is primarily the function of the hypothalamus and skin, not the kidneys. Additionally, while the kidneys play a role in regulating blood pressure through the secretion of renin and fluid balance, this is a secondary function to their main role in waste removal. Therefore, the most accurate answer regarding the kidneys’ primary function is their ability to filter waste from the blood.