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Ureters are two thin ducts that transport urine from the kidneys to the bladder. Each one measures nearly 30 centimeters long and six to eight millimeters in diameter. The walls of these structures are split into three layers: adventitia, the outermost layer, is made up of connective tissue containing an abundance of blood and lymph vessels and nerves; the intermediate layer is called muscular or muscularis (formed by smooth muscle fibers) and the innermost layer is called mucosa; it consists of an epithelium (tissue) that surrounds it.

Although they are only a passageway, ureters are not passive. Through a series of contractions and relaxations of their walls, ureters push their contents forward. At the junction with the bladder, we find the orifices of the ureters, which are valves that make sure urine only flows in one direction.

The urinary bladder is a muscular pouch where urine coming from the kidneys is stored. It is protected by the osseous walls of the pelvis and can blowup like a balloon as it intakes urinary waste, until it reaches its limit and must evacuate the urine. This job depends on the muscles that make up this region. When the bladder is empty, the muscles are relaxed and their inner coating presents a series of folds; but as the bladder fills up, the muscles contract and the walls begin to stretch. The same as ureters, the bladder wall also has three layers:

Mucosa, the innermost layer. It is highly adapted to withstand the acidity of urine. In addition, it contains long, cylindrical cells that are in charge of warning the bladder it has reached its storage limit.
Muscular or intermediate layer. It is formed by muscle fibers that crisscross in different directions.
Serosa is the outermost layer.

The urethra is the final stretch urine passes through and it is through here that it is expelled from the body. It is a tube made up of two layers, a mucosa and a muscular layer. They facilitate the evacuation of urine. Anatomically, this organ is different in men and women. The male urethra is longer and passes through the penis. The female urethra is considerably smaller and it is the final portion of the urinary tract, which means it is in charge of transporting urine to the outside world.

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