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

The primary function of the kidneys is to filter blood and produce urine. This vital process helps maintain the body's homeostasis by removing waste products and excess substances from the bloodstream. As blood passes through the kidneys, waste materials such as urea, creatinine, and toxins are filtered out, and the necessary components, such as water, electrolytes, and certain nutrients, are reabsorbed back into the bloodstream as needed. The end product of this filtering process is urine, which is excreted from the body, eliminating waste and helping to regulate the balance of fluids and electrolytes.

While other options highlight important functions related to the kidneys, they do not embody the kidneys' primary role as efficiently as filtering blood and producing urine does. The kidneys do produce hormones, such as erythropoietin and renin, which play roles in red blood cell production and blood pressure regulation, respectively; however, these functions are secondary to their primary role in urine formation. Absorbing nutrients primarily takes place in the gastrointestinal tract, and while the kidneys do help regulate blood pressure through fluid balance and hormonal production, this function is not the primary task of the kidneys. Thus, the main function concentrated on filtering blood and producing urine is essential for maintaining the body's