29.23 : Urethra

The urethra is a hollowed tubular organ through which urine is expelled from the body. This structure extends from the bladder to the external opening, allowing urine to be released.

The anatomy of the urethra differs between males and females. In females, the urethra is short, measuring about 3–4 cm in length, and opens anterior to the vaginal opening. In males, the urethra is longer and passes through the penis, serving dual purposes: expelling urine and ejaculating semen. The male urethra is divided into three distinct regions:

1. Prostatic Urethra: The widest portion, located below the bladder, passes through the prostate gland.
2. Membranous Urethra: A short segment connecting the prostatic and spongy urethras.
3. Spongy Urethra: The longest section, surrounded by erectile tissue, runs the length of the penis and ends at the external urethral orifice.

Both males and females have two sphincters that regulate the flow of urine:

1. Internal Urethral Sphincter: Located at the bladder-urethra junction, this sphincter is composed of smooth muscle circular fibers. The autonomic nervous system controls it and prevents involuntary urine leakage, maintaining bladder continence.
2. External Urethral Sphincter: Positioned where the urethra passes through the urogenital diaphragm, this sphincter is made of skeletal muscle and is under conscious control. It allows voluntary initiation or suppression of urination.

The urethra is essential for the excretion of urine and, in males, for the ejaculation of semen. Understanding the anatomy and function of the urethra is crucial for diagnosing and managing conditions such as urinary tract infections, incontinence, and other disorders of the urinary system.