The urethra is a tube that serves as the exit pathway for urine from the body. It connects directly to the bladder, which stores urine, allowing for its controlled release. This muscular tube plays a fundamental role in the excretory system, ensuring the removal of waste fluids.
Urethral Anatomy and Location
The urethra’s location and structure vary significantly between males and females. In both sexes, it originates at the base of the urinary bladder and extends to the outside of the body. The tubular structure is composed of epithelial tissue, smooth muscle cells, and connective tissue, forming a passage for fluids.
The female urethra is a relatively short tube, measuring about 3 to 4 centimeters (1.5 inches) in length. It begins at the bladder neck and opens to the outside between the clitoris and the vaginal opening. Its short length can influence susceptibility to urinary tract infections.
In contrast, the male urethra is considerably longer, typically measuring about 18 to 20 centimeters (7 to 8 inches). It extends from the bladder, passes through the prostate gland, and then traverses the entire length of the penis. This longer path means it is divided into distinct segments, including sections that pass through the prostate and the erectile tissue of the penis.
Role in Urine Excretion
The primary function of the urethra is the controlled elimination of urine from the bladder, a process known as urination. The bladder expands as it fills with urine, and when a certain volume is reached, nerve signals are sent to the brain, indicating the need to urinate. For urination to occur, a coordinated action between the bladder and urethral muscles is necessary.
Two main muscle structures, called urethral sphincters, regulate urine flow. The internal urethral sphincter is located at the junction where the urethra leaves the bladder. This sphincter is made of smooth muscle and is under involuntary control, maintaining a closed state to prevent urine leakage.
Further along the urethra is the external urethral sphincter, which is composed of skeletal muscle. This sphincter is under voluntary control, allowing individuals to decide when to start or stop urine flow. During urination, both the internal and external sphincters relax, while the bladder muscle contracts, expelling urine through the urethra.
Male Urethra’s Dual Role
The male urethra possesses an additional function beyond urine excretion, serving as a conduit for the reproductive system. It transports semen, the fluid containing sperm, out of the body during ejaculation.
During ejaculation, sperm travels from the testes and mixes with fluids produced by the seminal vesicles and the prostate gland, forming semen. This semen then enters the urethra to be expelled. The prostate gland contributes to the forceful expulsion of semen.
To prevent urine and semen from mixing or being expelled simultaneously, the male body employs a precise mechanism. The internal urethral sphincter, located at the bladder neck, contracts during ejaculation. This contraction closes off the bladder, preventing semen from entering it and stopping urine from entering the urethra.