What is the primary function of the urinary bladder?

• A. Filters blood
• B. Temporary reservoir for urine
• C. Produces urine
• D. Excretes waste

Answer: (B)

The urinary bladder’s main job is to store urine until you’re ready to urinate. Urine is formed by the kidneys and then flows down to the bladder via the ureters. The bladder expands as it fills, thanks to its stretchy wall (the detrusor muscle when relaxed and the transitional epithelium lining). During storage, the detrusor muscle stays relaxed and the internal sphincter remains closed, with voluntary control over the external sphincter helping to hold urine in. When you decide to void, signaling from the nervous system causes the detrusor to contract and the sphincters to relax, allowing urine to be expelled through the urethra. In adults, typical comfortable filling is about 300–500 mL, with the urge to void appearing as it nears 400–600 mL.