What is the functional unit of the kidney?

• A. Nephron
• B. Nephrite
• C. Nerve cell
• D. Nodule

Answer: (A)

The nephron is the functional unit of the kidney, performing filtration, reabsorption, secretion, and urine formation. Each kidney contains about a million nephrons, and their structure—the glomerulus plus the tubular system (Bowman’s capsule, proximal tubule, loop of Henle, distal tubule, and collecting duct)—enables blood filtration and the precise handling of water, electrolytes, and wastes. The glomerulus filters plasma to form filtrate, which then passes through the tubules where most water and solutes are reabsorbed and wastes may be secreted, producing urine that is ultimately collected and excreted.

Nephrite is a gemstone (jade), not a kidney structure. A nerve cell is part of the nervous system, not the kidney’s functional unit. A nodule is a small lump of tissue, not a specialized unit for urine formation.