Figure 2 : Anatomy and histology of the female bladder.

From: Urinary incontinence in women

Figure 2

The bladder lies immediately behind the pubic bones. When empty, the bladder has a pyramidal shape. As it fills and distends, the bladder balloons up above the pubic bones in an ovoid shape. The muscle of the bladder wall (the detrusor) consists of interdigitating fibres of smooth muscle, arranged in circular and longitudinal layers. These can stretch up to four times their resting length, so there is no increase in linear tension (or pressure) during normal bladder filling. The bladder and the ureters are both lined by a transitional epithelium, the urothelium. It contains flattened (‘umbrella’) cells and cuboidal cells, which also enable stretch as the bladder fills. The base of the bladder is a triagonal area, called the trigone. The ureters enter at the two superior corners of this triangle and the bladder neck lies at the inferior corner. The bladder neck is in continuity with the urethra, which, in women, is 2.5–4 cm long. The internal sphincter is formed of rings of smooth muscle at the bladder neck, whereas the external sphincter is formed by the muscles of the pelvic floor. Both sphincters help to close off the urethra to maintain continence.