The human organ primarily responsible for filtering blood is the kidneys. These two bean-shaped organs are located in the lower back and play a crucial role in the body's waste management system. They filter out excess fluids, toxins, and waste products from the bloodstream, excreting them as urine. Additionally, the kidneys help regulate blood pressure, maintain electrolyte balance, and produce hormones that are vital for red blood cell production and calcium metabolism. Overall, the kidneys are essential for homeostasis, ensuring that the body's internal environment remains stable and healthy.