Which organ is responsible for collecting urine within the urinary system?

The bladder is the organ specifically responsible for collecting and storing urine within the urinary system. As urine is produced by the kidneys, it travels down the ureters and enters the bladder, where it can accumulate until it reaches a certain volume that triggers the sensation of needing to urinate. The bladder is a muscular, expandable pouch that can hold a significant amount of urine, typically around 400-600 mL in adults, allowing for controlled elimination of urine from the body.

The kidneys, while essential for urine production and filtration, do not collect urine; instead, they continuously filter blood and produce urine that then flows to the bladder through the ureters. The ureters serve as the conduits for urine transportation from the kidneys to the bladder, facilitating the movement but not storage. The urethra is the final tube that carries urine from the bladder to the outside of the body, playing a role in the elimination process rather than collection. Therefore, the bladder's function as a reservoir for urine makes it the correct answer in this context.