• Anatomic Location and Structure
• Ureters and Urethra
• Blood and Lymph Supply
• Innervation

Anatomic Location and Structure

In both males and females, the bladder lies behind the pubic symphysis from which it is separated by the retropubic space (1). In females, the bladder is located anterior to the uterus, whereas in males, it lies in front of the seminal vesicles and above the prostate gland (2). Posteriorly, the base of the bladder in both males and females is located in front of the rectum.

Anatomically, the bladder consists of two regions. Its lower region contains the trigone, a triangular area whose upper vertices on the right and left are marked by the entry points of the respective ureters, which transport urine into the bladder from the kidneys. The third, more forward vertex of the trigone, is the point at which the urethra exits the bladder. The size, shape and relationship off the bladder to surrounding structures vary with its urine content. Because it is essentially fixed by ligaments to the underlying muscle of surrounding structures, the trigone of the bladder changes little in its relationship to those structures as the bladder fills with urine. However, as the bladder fills, its remaining distensible portion (fundus) rises from the pelvis, protruding into the abdominal cavity with its apex reaching the level of the umbilicus.

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Structure

Ureters and Urethra

The two ureters, which carry urine from the right and left kidneys into the bladder, originate in the funnel shaped collecting region or pelvis of each kidney, entering the bladder wall, they pass through it over a distance of approximately 2 cm before opening into the bladder cavity or lumen. (1,4). The ureters consist of three tissue layers, of which the outermost layer is made up of fibrous tissue, the medial layer of the medial layer of muscle, and the inner or mucosal layer of epithelial tissue (1).

Extending downward from the bladder at the lower, forward most vertex of the bladder trigone, the urethra carries urine out of the body. In females, the urethra is approximately 4 cm long and has its external opening just above the vaginal orifice (1). In males, the urethra is about 20 cm in length and passes through the penis, ending in the external urethral orifice at the top of this organ.

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Blood and Lymph Supply

The urinary bladder receives its blood supply through the superior, middle and inferior vesical arteries, all of which are branches of the internal iliac artery. The veins that carry blood from the vesical venous plexus, which drains into the internal iliac veins (5). Within the upper regions of the bladder are lymphatic vessels that carry lymphatic vessels that carry lymph to the external lymph nodes. The lower regions of the bladder contain the lymphatic vessels that drain into the internal iliac lymph nodes. Some other lymphatic vessels, in the neck of the bladder at the site of exit of the urethra, drain into the sacral and common iliac lymph nodes (5).

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Innervation

The bladder is innervated by afferent branches of the visceral nervous system, which transmit sensations of pain to the spinal cord and brain by branches of both the parasympathetic and sympathetic divisions of the autonomic or peripheral nervous system. The parasympathetic innervation of the bladder is derived from splanchnic nerves of the pelvis. These nerves provide motor stimuli to the bladder muscle and, when activated by stretching, cause the contraction of this muscle and relaxation of the sphincter muscles of the urethra, thereby promoting the expulsion of urine from the bladder. In contrast to the parasympathetic innervation of the bladder, its sympathetic innervation (which is derived from thoracic nerves 11 and 12 lumbar nerves 1 and 2) inhibits constriction of the bladder wall and promotes contraction of the urinary sphincters, restricting the excretion of urine (5).

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References