What is the structure of the urinary bladder?

The bladder is composed of four layers of tissues. The outermost serous membrane is a thin membrane lining the closed cavities of the body and has two layers with a space in-between that is filled with the serous fluid which covers only the superior surface of the bladder. Next layer is a muscle layer composed of longitudinal and circular muscle fibre.

Figure: Orifices of the bladder

The third layer is a sub-mucous layer containing blood vessels, lymphatics, sympathetic and parasympathetic nerves. The innermost layer is a mucous layer composed of transitional epithelium. There are three orifices in the bladder. The upper two orifices are the openings of the two ureters as illustrated in Figure. The inferior orifice is the point of origin of the urethra. These three orifices form a triangle described as the trigone of the bladder.