What is the main function of the kidneys?

The primary function of the kidneys is to filter waste products from the blood and produce urine, making the correct answer the one that emphasizes this critical role. The kidneys work as vital organs in the urinary system, where they continuously clean the blood by removing excess substances, toxins, and metabolic waste. Through this filtration process, they help maintain homeostasis by regulating key parameters, such as electrolyte balance, fluid balance, and blood pressure.

In addition to waste filtration, the kidneys also play a role in regulating acid-base balance and the body's overall fluid volume. The urine produced, which consists of the filtered waste and excess substances, is then expelled from the body, thereby contributing to the elimination of waste materials. This intricate process is fundamental for maintaining the body's internal environment and ensuring that harmful substances do not accumulate in the bloodstream.

While the kidneys also have secondary functions, such as producing hormones like erythropoietin, which stimulates red blood cell production, and managing vitamin D metabolism, their primary role is centered around waste filtration and urine production. This central function is critical for overall health and well-being.