Anatomy of the Genitourinary System II: Bladder and Urethra

The bladder wall has four distinct layers. The outer adventitia provides structural support. The detrusor muscle, composed of smooth muscle fibers, contracts to expel urine during urination. The submucosa contains blood vessels and nerves that supply the bladder. The innermost urothelium, made of transitional epithelium, prevents urine from being reabsorbed into the body.

In females, the bladder is positioned anterior to the vagina and inferior to the uterus. In males, the bladder is located superior to the prostate gland. Both are situated behind the pubic bone. These anatomical differences reflect the distinct reproductive organ arrangements in each sex.

The trigone is a triangular area at the base of the bladder formed by the ureteral and urethral openings. It directs urine from the bladder into the urethra during urination. This specialized region acts as a funnel, facilitating the smooth transition of urine from storage to expulsion.

The male urethra extends approximately 20 to 25 centimeters through the penis and is surrounded by the prostate gland, whereas the female urethra is only 2.5 to 5 centimeters long. In males, the urethra serves a dual function, transporting both urine and semen. The longer male urethra reflects this additional reproductive role.

The internal urethral sphincter is an involuntary smooth muscle that remains closed to retain urine and relaxes during urination. The external urethral sphincter is composed of voluntary striated muscle, providing conscious control over urine flow. Together, these sphincters regulate urination by allowing individuals to start or stop urine flow at will.

The bladder typically stores between 400 to 500 milliliters of urine. This muscular, stretchable organ expands to accommodate urine produced by the kidneys and maintains adequate storage capacity between voiding episodes. The bladder's expandable nature allows it to adjust to varying volumes of urine throughout the day.

The urothelium is the innermost lining of the bladder composed of transitional epithelium. This specialized tissue layer acts as a barrier, preventing urine from being reabsorbed into the body. The urothelium maintains the integrity of stored urine until it is expelled through the urethra during urination.