Urinary Bladder

The urinary bladder is a hollow, muscular sac that temporarily stores urine before micturition. It can hold approximately 600 mL of urine and is retroperitoneally situated on the pelvic floor behind the pubic symphysis. In males, it sits directly in front of the rectum, while in females, it is positioned anterior to the vagina and below the uterus.

The trigone is a small inverted triangular area on the bladder floor formed by two ureteric orifices and the internal urethral orifice. This specialized region marks where urine enters the bladder from the ureters and exits through the urethra. The trigone serves as an important anatomical landmark for bladder structure and function.

The bladder wall consists of three layers: the mucosa, muscularis, and adventitia. The innermost mucosa contains specialized folds called rugae composed of transitional epithelium that allows the bladder to stretch without leakage. The muscularis layer contains smooth muscle fibers forming the detrusor muscle, while the outermost adventitia is continuous with the ureters and covers posterior and inferior surfaces.

Transitional epithelium, also called urothelium, forms specialized folds called rugae in the bladder mucosa. This tissue permits the bladder to stretch significantly as it fills with urine while maintaining a watertight barrier to prevent leakage during storage. The elastic properties of transitional epithelium allow the bladder to accommodate varying volumes of urine efficiently.

The detrusor muscle is formed by the muscularis layer of the bladder wall, consisting of circular smooth muscle fibers sandwiched between inner and outer longitudinal layers. This muscle regulates bladder volume and enables the expulsion of urine during micturition. The coordinated contraction of the detrusor muscle is essential for emptying the bladder completely.

The bladder's superior surface is covered by the peritoneum, while the posterior and inferior surfaces are covered by the adventitia, which is continuous with the ureters. This arrangement reflects the bladder's retroperitoneal position within the pelvic cavity. The peritoneal covering on the superior surface allows the bladder to expand upward into the abdominal cavity as it fills.

In males, the bladder is positioned directly in front of the rectum, whereas in females, it is located anterior to the vagina and below the uterus. These positional differences reflect the distinct reproductive anatomy of each sex. Despite these anatomical variations, the bladder's basic structure, capacity, and function remain consistent between males and females.