What is the major organ of the urinary system, described as bean-shaped?

• A. Bladder
• B. Kidney
• C. Ureter
• D. Meatus

Answer: (B)

The kidney is the major organ of the urinary system and is bean-shaped. It sits in the back of the abdomen (retroperitoneal) and filters blood through tiny units called nephrons, removing wastes and extra fluids to form urine. Each kidney contains about a million nephrons, and they help regulate fluid and electrolyte balance, maintain acid-base balance, and influence blood pressure and red blood cell production. The bean shape comes from its curved outer surface and a notch called the hilum, where the renal artery enters, and the renal vein and ureter exit. Urine then flows from the kidneys into the bladder via the ureters. The other structures—bladder (stores urine), ureter (transports urine to the bladder), and meatus (the external urinary opening)—are parts of the system but not the bean-shaped major organ.