The primary role of the kidney in the human body is to **filter waste products and excess substances from the blood** to produce urine. Kidneys are critical for maintaining homeostasis, regulating body fluids, electrolyte balance, and blood pressure. They also play a key role in the regulation of acid-base balance and the production of hormones like erythropoietin, which stimulates red blood cell production. By filtering out toxins, urea, and other waste materials, kidneys help maintain overall health and the proper functioning of bodily systems. Proper kidney function is crucial for overall metabolic health.