The functional unit of the kidney is the nephron, consisting of the glomerulus, Bowman’s capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct. Each nephron filters blood, reabsorbs essential substances, and secretes waste, collectively forming urine. The nephron’s selective reabsorption and secretion capabilities maintain body fluid and electrolyte balance, regulate blood pressure, and eliminate waste products.