the bladder. The detrusor muscle is the muscular layer of the wall made of smooth muscle fibers arranged in spiral, longitudinal, and circular bundles. The detrusor muscle is able to change its length. It can also contract for a long time whilst voiding, and it stays relaxed whilst the bladder is filling. The wall of the urinary bladder is normally 3–5 mm thick. When well distended, the wall is normally less than 3 mm. Nearby structures In men, the prostate gland lies outside the opening for the urethra. The middle lobe of the prostate causes an elevation in the mucous membrane behind the internal urethral orifice called the uvula of urinary bladder. The uvula can enlarge when the prostate becomes enlarged. The bladder is located below the peritoneal cavity near the pelvic floor and behind the pubic symphysis. In men, it lies in front of the rectum, separated by the recto-vesical pouch, and is supported by fibres of the levator ani and of the prostate gland. In women, it lies in front of the uterus, separated by the vesico-uterine pouch, and is supported by the elevator ani and the upper part of the vagina. Blood and lymph supply The bladder receives blood by the vesical arteries and drained into a network of vesical veins. The superior vesical artery supplies blood to the upper part of the bladder. The lower part of the bladder is supplied by the inferior vesical artery, both of which are branches of the internal iliac arteries. In females, the uterine and vaginal arteries provide additional blood supply. Venous drainage begins in a network of small vessels on the lower surfaces of the bladder, which coalesce and travel with the lateral ligaments of the bladder into the internal iliac veins. The lymph drained from the bladder begins in a series of networks throughout the mucosal, muscular and serosal layers. These then form three sets of vessels: one set near the trigone draining the bottom of the bladder; one set draining the top of the bladder; and another set draining the outer undersurface of the bladder. The majority of these vessels drain into the external iliac lymph nodes. Nerve supply The bladder receives both sensory and motor supply from sympathetic and the parasympathetic nervous systems. The motor supply from both sympathetic fibers, most of which arise from the superior and inferior hypogastric plexuses and nerves, and from parasympathetic