The organ responsible for filtering blood in the kidneys is known as the nephron. Each kidney contains about a million nephrons, which play a vital role in the renal system. They filter waste products and excess substances from the blood, regulate electrolyte levels, and maintain homeostasis. The filtration process occurs in the glomerulus, followed by reabsorption and secretion in the renal tubule, resulting in the formation of urine that excretes waste while conserving nutrients.