21.5: Urinary Bladder
- Page ID
- 53834
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The urinary bladder stores urine until it is expelled from the body. Its inner lining is transitional epithelium, tissue that expands when not stretched and becomes thinner, similar to stratified squamous epithelium, when stretched. This allows the bladder to expand to provide more room for storing urine. The inner lining of the urinary bladder also has folds of tissue called rugae that similarly can stretch to enable the organ to expand and stretch when filled with urine.
Above: Urinary bladder in a male (females do not have a prostate gland).
A triangular structure, called the trigone, is found on the posterior wall of the urinary bladder. The trigone as three openings: on the right, the right ureteral opening, on the left, the left ureteral opening, and inferiorly, the internal urethral orifice leading to the urethra.
Detrusor muscles are present in the walls of the bladder. When contracted, the detrusor muscle pushes urine from the urinary bladder and into the urethra to expel urine during urination.
Above: The bladder is lined by transitional epithelium. The underlying lamina is composed of a thinner, highly cellular portion adjacent to the epithelium and a thicker region of dense connective tissue closer to muscularis externa. The muscularis externa is composed of three ill-defined layers of smooth muscle (inner and outer longitudinal and middle circular layers). An adventitia is present beyond the muscularis externa. Tissue is magnified by 100x.
Above: The mucosa of the bladder has a histologic appearance very similar to that of the ureter. Transitional epithelium has characteristic dome-shaped cells at the surface when the bladder is not distended with urine. Dome cells are often bi-nucleated and become flattened when the bladder is distended. A connective tissue layer (lamina propria continuous with submucosa) underlies this epithelium. Tissue is magnified by 400x.
Attributions
- "Digital Histology" by Department of Anatomy and Neurobiology and the Office of Faculty Affairs, Virginia Commonwealth University School of Medicine and the ALT Lab at Virginia Commonwealth University is licensed under CC BY 4.0
- "Illu bladder.jpg" by U.S. National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) Program is in the Public Domain
- "Renal Anatomy" by Dongho Kim is licensed under CC BY-NC-SA 4.0