What does the urethra do in the urinary system?

The role of the urethra within the urinary system is specifically to direct urine out of the bladder. When the bladder fills with urine, nerve signals prompt the muscles of the bladder to contract, pushing the urine into the urethra. The urethra then serves as the conduit for urine to exit the body. This function is critical for the process of urination, allowing for the controlled expulsion of waste fluid.

The other options represent different functions of the urinary system but do not accurately describe the role of the urethra. The kidneys are responsible for filtering waste from the blood, and the bladder is responsible for temporarily storing urine before it is expelled through the urethra.