Human Anatomy - M.M. Kurepina, A.P. Ozhigova, A.A. Nikitina 2010

Internal Organs
Urinary System
Urinary Bladder

The Urinary Bladder (vesica urinaria) is an unpaired hollow organ holding an average of 750 cm³ of fluid, located in the anterior part of the pelvic cavity behind the Pubic Symphysis (Atl. Fig. 202). When distended, the urinary bladder becomes pear-shaped and projects significantly above the superior border of the symphysis. The bladder is divided into an apex, directed upward and forward, a middle part—the body, and a fundus, on the posterior wall of which both Ureters open and the Urethra begins. In males, the Seminal Vesicles, Ductus Deferentes, and the superior part of the Prostate Gland lie adjacent to the Cytology/practical/108.html">Fundus of the bladder (Fig. 4.44). In females, the fundus of the bladder borders the anterior vaginal wall and the cervix of the Uterus.

The bladder wall is highly distensible. When the bladder is empty, its thickness can reach 15 mm, whereas in the distended state, it thins to 2–3 mm. The bladder wall consists of the mucosa, muscularis, and adventitia (Connective Tissue layer). Superiorly and posteriorly, the urinary bladder is covered by Peritoneum.

The mucosa is lined with transitional epithelium, which is capable of flattening during distension. It forms numerous folds that flatten out as the bladder fills (Atl. Fig. 206). In the anterior part of the fundus of the bladder, there are three orifices arranged in a triangular shape. The internal urethral orifice lies inferiorly, while the right and left ureteric orifices are located superiorly (Fig. 4.45). At the opening of each Ureter, There is a permanent fold, or valve, which acts as a one-way valve. This valve, along with the oblique angle at which the ureters pierce the bladder wall, prevents the backflow of urine from the bladder into the ureters.

The muscularis consists of smooth Muscle arranged in three layers. In the outer and inner layers, the muscle bundles run longitudinally, while in the middle, most developed layer, they run circularly. Contraction of the muscularis leads to the emptying of the urinary bladder. The urethral orifice in the wall of the urinary bladder is surrounded by circular muscle fibers of the sphincter vesicae, or internal urethral sphincter, which relaxes during urination.

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Fig. 4.44. Male urinary bladder (posterior view):

1 — right ureter; 2 — apex; 3 — body and 4 — fundus of the urinary bladder; 5 — ampulla of the Ductus deferens; 6 — Seminal Vesicle; 7 — prostate gland; 8 — membranous part of the urethra; 9 — Bulbourethral gland; 10 — peritoneum

Fig. 4.45. Urinary bladder:

1 — ureteric orifices; 2 — fundus of the urinary bladder; 3 — urethral orifice

The venous and nerve plexuses are located in the adventitia, which merges into the perivesical connective tissue. The median umbilical ligament—a remnant of the urachus covered by peritoneum—extends from the apex of the bladder to the umbilicus. Additionally, the urinary bladder is anchored by ligaments to the pubic bones, and to the anterior and posterior abdominal walls.