Human Anatomy and Physiology - N. I. Fedyukovich 2003

Internal Organs
Urogenital System
Urinary Bladder

The Urinary Bladder (vesica urinaria) is an unpaired hollow organ that accumulates urine (250—500 ml); it is located on the floor of the lesser pelvis. Its shape and size depend on the degree of filling with urine.

The urinary bladder is divided into the apex, body, fundus, and neck. The anterosuperior part of the bladder, directed toward the anterior abdominal wall, is called the apex of the bladder. The transition of the apex into the wider part of the bladder forms the body of the bladder, which extends downward and backward to become the Cytology/practical/108.html">Fundus of the bladder. The lower part of the bladder tapers like a funnel and transitions into the Urethra. This part is called the neck of the bladder. The internal urethral orifice is located in the lower portion of the bladder neck.

The wall of the urinary bladder consists of a mucosa, a submucosa, a muscularis, and an adventitia (Connective Tissue coat), and, in areas covered by the Peritoneum, a serosa (serous membrane). When the bladder is filled with urine, its walls are stretched and thin (2—3 mm), whereas after emptying, their thickness reaches 12—15 mm. The mucosa is lined with transitional epithelium and forms numerous folds.

In the anterior part of the fundus of the bladder, there are three openings: the two ureteric orifices and the internal urethral orifice. Between them lies the trigone of the bladder (vesical trigone), where the mucosa is tightly adherent to the muscular layer.

The muscular coat consists of outer longitudinal, middle circular, and inner oblique-longitudinal layers of smooth Muscle fibers, which are closely interconnected. In the region of the bladder neck, the middle layer forms the internal urethral sphincter (sphincter vesicae) around the internal urethral orifice.

Upon contraction, the muscular coat expels urine through the urethra.

Externally, the urinary bladder is covered by a connective tissue adventitia, and superiorly, as well as partially on the left and right, by the peritoneum. Anterior to the bladder is the Pubic Symphysis; posterior to it, in males, are the Seminal Vesicles, the ampullae of the Ductus Deferentes, and the rectum, and in females, the Uterus and the upper part of the Vagina. Inferiorly, the urinary bladder rests on the Prostate Gland in males and on the pelvic floor in females.