Urethra

The urethra is a tube that connects the urinary bladder to the urinary meatus for the removal of urine from the body. It also serves to expel semen (containing sperm) in males. The urethra differs in length and function between males and females.

In females, the urethra is relatively short, typically around 4 cm (1.5 inches) long. It originates at the internal urethral orifice of the bladder and terminates at the external urethral orifice, located anterior to the vaginal opening. The female urethra's primary function is the expulsion of urine.

In males, the urethra is significantly longer, approximately 20 cm (8 inches), and is divided into four sections: the preprostatic (intramural), prostatic, membranous, and spongy (penile) urethra. The preprostatic urethra is the shortest segment, passing through the bladder neck. The prostatic urethra passes through the prostate gland and receives secretions from both the prostate and ejaculatory ducts. The membranous urethra is a short, narrow section that passes through the urogenital diaphragm. The spongy urethra, also known as the penile urethra, is the longest section and runs through the length of the penis, terminating at the external urethral orifice. The male urethra serves the dual purpose of urine expulsion and semen ejaculation.

The walls of the urethra contain smooth muscle and are lined with a mucous membrane. The specific type of epithelium lining the urethra varies along its length, but typically includes transitional epithelium near the bladder and stratified squamous epithelium near the external opening.

Common conditions affecting the urethra include urethritis (inflammation of the urethra), urinary tract infections (UTIs), urethral strictures (narrowing of the urethra), and urethral cancer. Catheterization, a procedure involving the insertion of a tube into the urethra to drain the bladder, can sometimes be necessary for medical reasons.