The functional unit of the kidney is:The capillariesThe nephronThe renal artery and vein

The functional unit of the kidney is known as the nephron. Each kidney contains about a million nephrons, which are responsible for filtering blood, reabsorbing essential substances, and excreting waste products as urine. The nephron comprises several components, including the renal corpuscle (which contains the glomerulus and Bowman's capsule) and the renal tubule (which includes the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting ducts). This intricate structure allows for the essential processes of filtration, secretion, and reabsorption that are crucial for maintaining the body's fluid and electrolyte balance.