What best describes the urinary bladder?

• A. A hollow, muscular sac that holds and stores urine
• B. A network of tubes that filter urine
• C. A hormone gland
• D. A muscle that pumps blood

Answer: (A)

The bladder serves as a reservoir in the urinary system. It is a hollow, muscular sac that stores urine until you’re ready to empty it. Its smooth muscle, the detrusor, relaxes to fill and then contracts to expel urine when you urinate, working with the sphincters to control the flow. This storage function distinguishes it from other organs: the kidneys are made up of tubules that filter blood to form urine, an endocrine gland releases hormones, and the heart is a muscular pump that moves blood. So the bladder’s primary role is to hold urine, not filter it, produce hormones, or pump blood.