What is the functional unit of the kidney?

• A. Nephron
• B. Cortex
• C. Glomerulus
• D. Ureter

Answer: (A)

The functional unit of the kidney is the nephron. Each nephron carries out the essential tasks of filtering blood, reabsorbing needed substances, and secreting waste into a tubular fluid to form urine. It starts with Bowman's capsule surrounding the glomerulus, where blood plasma is filtered. The filtrate then moves through the proximal tubule, loop of Henle, distal tubule, and collecting duct, with most water, ions, and nutrients reabsorbed and additional wastes secreted as needed. This coordinated processing concentrates urine and regulates fluid and electrolyte balance. The kidney contains roughly a million nephrons per organ, and while the cortex contains many nephrons, the glomerulus is just a part of a nephron, not the entire functional unit, and the ureter is simply the tube that carries urine to the bladder.