What is the primary function of the kidneys in the human body?

The primary function of the kidneys is to filter waste products and excess substances from the blood. This crucial role ensures that harmful waste, such as urea, creatinine, and various toxins, are effectively removed from the bloodstream through the formation of urine. Additionally, the kidneys help regulate the body’s fluid balance, electrolyte levels, and acid-base balance, which are all essential for maintaining homeostasis. By excreting excess water and solutes, the kidneys play a key role in controlling blood pressure and overall body fluid composition, making their filtering capability fundamental to health and well-being.

The other options, while mentioning important bodily functions, do not pertain primarily to the kidneys. For example, hormone production is more closely associated with glands like the pituitary or thyroid, temperature regulation is primarily facilitated by processes in the hypothalamus and through skin mechanisms, and nutrient absorption occurs mainly in the gastrointestinal tract. Recognizing the kidneys' specific filtering role helps highlight their importance in the body’s physiological processes.