The primary function of the kidneys is to filter and excrete waste products from the bloodstream while regulating the body's fluid balance, electrolyte levels, and blood pressure. Each kidney contains tiny filtration units called nephrons, which remove waste products, excess salts, and fluids to form urine. This urine is then excreted through the urinary tract. Additionally, kidneys play a critical role in maintaining homeostasis by producing hormones like erythropoietin, which stimulates red blood cell production, and renin, which helps regulate blood pressure. The kidneys also help manage the body's acidity or alkalinity, ensuring the internal environment remains stable.