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

The primary function of the kidneys in the human body is to filter blood. They play a crucial role in the urinary system by removing waste products, excess substances, and toxins from the blood, which are then excreted as urine. This filtration process helps maintain the body's fluid balance, electrolyte levels, and overall homeostasis. By regulating the composition of blood and ensuring that harmful substances are eliminated, the kidneys are essential for maintaining a stable internal environment.

While the kidneys do produce hormones, such as erythropoietin which helps regulate red blood cell production, their main and most critical function is blood filtration. The kidneys do not have a direct role in regulating body temperature or supporting bone health, although they can indirectly influence these functions through their regulation of minerals and fluids.