What is the primary function of the kidneys?

The primary function of the kidneys is to filter waste and excess fluid from the blood. This crucial role is performed through the nephrons, the functional units of the kidneys, which remove toxins, metabolites, and excess substances from the bloodstream, transforming them into urine for excretion. This filtering process helps maintain homeostasis by regulating the balance of fluids, electrolytes, and acids in the body. By removing waste products, the kidneys ensure that the internal environment remains stable and conducive to essential bodily functions.

The other options pertain to functions that are not primarily handled by the kidneys. Storing wounds and injuries does not relate to kidney function, as this is more relevant to the body's immune response and healing processes. The production of hormones for growth is primarily a function of the endocrine system and specific glands like the pituitary and thyroid. Lastly, regulating body temperature is mainly the responsibility of the hypothalamus and the integumentary system, through processes like sweating and shivering.