Bladder

It is a hollow organ, that is shaped like a bag, in which urine is stored after being filtered by the kidneys. The tubes that connect the kidneys to the bladder are the ureters.

The urine is expelled out through the urethra during urination.

While the bladder is filling, the muscle layer is relaxed and the muscles that close the entrance of the urethra (sphincter) remain contracted. During urination the muscle layer of the bladder contracts and the sphincter relaxes.