The bladder & urethra

The bladder
The bladder is a hollow, muscular organ that acts rather like a balloon in that it expands to collect and store urine. Urine is made up of water and waste products that your body does not need. It is produced in the kidneys and travels down to the bladder via tubes called ureters. When the bladder is full enough to empty, or you feel the need to pass urine, the urine travels out of the bladder, and subsequently the body, via another tube called the urethra.

The urethra
The urethra is the tube which connects the bladder with the outside of the body. The urethra allows urine to pass to the outside and, in men, allows passage of semen as well.

The external urethral sphincter is a striated muscle which allows voluntary control over voiding (emptying the bladder).

Female anatomy
The female urethra is 3-5cm long. The urethral opening is just above the vaginal opening.

Male anatomy
The male urethra is approximately 17.5cm long and opens at the end of the penis.