The urethra is a tube that connects the bladder to the outside of the body. It allows people and animals to remove urine from the body. People and animals control urination using the urethral sphincter.
The urethra is part of the urinary system in mammals. Because humans are mammals, they have urethras. In male mammals, the urethra is also a part of the reproductive system, because males use it as a tube for sperm during sex.
In human anatomy, men have longer urethras than women. This means that women have bladder infections more often, because their bladders are closer to the outside. Because the male urethra is longer and is not straight, inserting a catheter (tube to help urination) is more difficult in men.
In women, the urethra is 2.5-4 cm (1-1.5 in) long. Its opening to the outside of the body is part of the vulva (the area between a woman's legs). The female urethra is between the clitoris and the opening to the vagina. In men, the urethra is about 20 cm (8 in) long and its opening to the outside of the body is at the end of the penis.
The male urethra has three sections:
- The prostatic urethra crosses the prostate gland. The vas deferens also opens into the urethra in this section.
- The membranous urethra is a short section that goes through the urethral sphincter. It is 1 or 2 cm long, and is the narrowest (least wide) part of the urethra.
- The spongy or penile urethra goes through the penis on its lower side. This section is 15-16 cm (6 in) long and goes through the corpus spongiosum.
- The "bulbar" urethra.
- Urethritis is infection of the urethra. It often pain when urinating.
- Urethral syndrome is related to urethritis.
- Kidney stones that go through the urethra can be painful.
- To send a tube up the urethra to help drain urine is a common type of catheterization.
- To send a tube up the urethra to see the inside of the bladder is called cystoscopy.