The urinary bladder is situated immediately behind the pubic bone and anterior to the uterine cervix and upper vagina. It has a strong muscular wall consisting of three layers of interlacing fibres which are known together as the detrusor muscles (Fig. 1.14). The trigone is the only smooth part of the bladder as it is fixed to the underlying muscle. At the superior margins of the trigone lie the ureteric openings and at the inferior aspect the urethra.
Fig. 1.14 The bladder.
An interureteric ridge can often be visualized horizontally between the ureters at cystoscopy and is useful for orientation.
The rest of the bladder is highly distensible ensuring that as it is expanded the pressure of its contents remains the same.
The bladder receives its blood supply from the superior and inferior vesical arteries which originate from the internal iliac artery. The nerve supply is from the inferior hypogastric plexus. Sympathetic nerves arise in the first and second lumbar ganglia and the parasympathetic supply from the splanchnic nerves of the second, third and fourth sacral nerves.
The urethra is approximately 4 cm long in the female adult starting at the internal meatus of the bladder and passing through the pelvic floor to the vestibule. The epithelium is squamous near the external meatus and changes to transitional epithelium about two thirds of the way to the bladder. The deeper tissue is muscular and this maintains the urethral tone. There are no anatomical sphincters but the muscle fibres of the bladder at the internal meatus act as an 'internal sphincter' and the pelvic floor as a voluntary external sphincter.
The ureters run from the renal hilum to the trigone of the bladder and are approximately 30 cm in length. They enter the pelvis by passing over the common iliac bifurcation at the pelvic brim. They then pass along the lateral pelvic side wall before passing anteriorly and medially under the uterine artery as it originates from the internal iliac artery and into the base of the bladder. The ureter comes close to the ovarian artery and vein and can be adherent to these vessels or the overlying ovary in pathological cases. By passing close to the uterine artery it can be mistakenly clamped and divided as a rare complication of hysterectomy.
The ureters are muscular tubes lined by transitional epithelium. The blood supply varies during its course but small vessels along the surface of the ureter require careful preservation when dissecting it free from other structures.
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