Ureter and Urinary Bladder

A. Ureter

Is a muscular tube that transmits urine by peristaltic waves.
Has three constrictions along its course: at its origin where the pelvis of the ureter joins the ureter, where it crosses the pelvic brim, and at its junction with the bladder.
Crosses the pelvic brim in front of the bifurcation of the common iliac artery; descends retroperitoneally on the lateral pelvic wall; and runs medial to the umbilical artery and the obturator vessels and posterior to the ovary, forming the posterior boundary of the ovarian fossa.
In females, it is accompanied in its course by the uterine artery, which runs above and anterior to it in the base of the broad ligament of the uterus. Because of its location, the ureter is in danger of being injured in the process of hysterectomy. It can be remembered by the mnemonic device, water (ureter) runs under the bridge (uterine artery).
Passes posterior and inferior to the ductus deferens and lies in front of the seminal vesicle before entering the posterolateral aspect of the bladder in males.
Enters obliquely through the base of the bladder and opens by a slit-like orifice that acts as a valve, and the circular fibers of the intramural part of the ureter act as a sphincter. When the bladder is distended, the valve and sphincter actions prevent the reflux of urine from the urinary bladder into the ureter.
Receives blood from the aorta and the renal, gonadal, common and internal iliac, umbilical, superior and inferior vesical, and middle rectal arteries.

B. Urinary bladder

Is situated below the peritoneum and is slightly lower in the female than in the male.
Extends upward above the pelvic brim as it fills; may reach as high as the umbilicus if fully distended.
Has the apex at the anterior end and the fundus or base as its posteroinferior triangular portion
Has a neck, which is the area where the fundus and the inferolateral surfaces come together, leading into the urethra.
Has a uvula , which is a small eminence at the apex of its trigone, projecting into the orifice of the urethra. The trigone is bounded by the two orifices of the ureters and the internal urethral orifice, around which is a thick circular layer called the internal sphincter (sphincter vesicae).
Has bundles of smooth muscle fibers that, as a whole, are known as the detrusor muscle of the bladder.
Receives blood from the superior and inferior vesical arteries (and from the vaginal artery in females). Its venous blood is drained by the prostatic (or vesical) plexus of veins, which empties into the internal iliac vein.
Is innervated by nerve fibers from the vesical and prostatic plexuses. The parasympathetic nerve stimulates to contract the musculature (detrusor) of the bladder wall, relaxes the internal urethral sphincter, and promotes emptying. The sympathetic nerve relaxes the detrusor of the bladder wall and constricts the internal urethral sphincter.

C. Micturition (urination)

Is initiated by stimulating stretch receptors in the detrusor muscle in the bladder wall by the increasing volume (about 300 mL for adults) of urine.
Can be assisted by contraction of the abdominal muscles, which increases the intra-abdominal and pelvic pressures.
Involves the following processes:

Sympathetic (general visceral efferent [GVE]) fibers induce relaxation of the bladder wall and constrict the internal sphincter, inhibiting emptying. (They may also activate the detrusor to prevent the reflux of semen into the bladder during ejaculation.)
General visceral afferent (GVA) impulses arise from stretch receptors in the bladder wall and enter the spinal cord via the pelvic splanchnic nerves.
Parasympathetic preganglionic (GVE) fibers in the pelvic splanchnic nerves synapse in the pelvic (inferior hypogastric) plexus; postganglionic fibers to the bladder musculature induce a reflex contraction of the detrusor muscle and relaxation of the internal urethral sphincter, enhancing the micturition.
General somatic efferent (GSE) fibers in the pudendal nerve cause voluntary relaxation of the external urethral sphincter, and the bladder begins to void.
At the end of micturition, the external urethral sphincter contracts, and bulbospongiosus
muscles in the male expel the last few drops of urine from the urethra.

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