The organ responsible for filtering blood in the human body is the kidneys. These two bean-shaped organs are located on either side of the spine and play a vital role in maintaining homeostasis by regulating the composition of blood. Kidneys filter out waste products, excess salts, and fluid, which are excreted as urine. They also help regulate blood pressure, electrolyte balance, and acid-base balance. Through these functions, the kidneys significantly contribute to maintaining the body's internal environment, showcasing their importance in renal physiology.