Urethra

In anatomy, the urethra is a tube which connects the urinary bladder to the outside of the body. The urethra has an excretory function in both genders to pass urine to the outside, and also a reproductive function in the male, as a passage for sperm.

The external urethral sphincter is a striated muscle that allows voluntary control over urination.

Female urethra
In the human female, the urethra is about 1-2 inches long and opens in the vulva between the clitoris and the vaginal opening.

Because of the short length of the urethra, women tend to be more susceptible to infections of the bladder (cystitis) and the urinary tract.

Male urethra
In the human male, the urethra is about 8 inches (20 cm) long and opens at the end of the penis. The inside of the urethra has a spiral groove (like rifling in a gun barrel), which makes the urine flow in a wide stream.

The urethra is divided into three parts in men, named after the location:

The length of a male's urethra, and the fact it contains a number of bends, makes catheterisation more difficult.

Histology
The epithelium of the urethra starts off as transitional cells as it exits the bladder. Further along the urethra there are stratified columnar cells, then stratified squamous cells near the external meatus (exit hole).

There are small mucus-secreting urethral glands, that help protect the epithelium from the corrosive urine.

Medical problems of the urethra
Endoscopy of the bladder via the urethra is called cystoscopy.
 * Hypospadias and epispadias are forms of abnormal development of the urethra in the male, where the opening is not quite where it should be (it occurs lower than normal with hypospadias, and higher with epispadias). In a severe chordee, the urethra can develop between the penis and the scrotum.
 * Infection of the urethra is urethritis, said to be more common in females than males. Urethritis is a common cause of dysuria (pain when urinating).
 * Related to urethritis is so called urethral syndrome
 * Passage of kidney stones through the urethra can be painful and subsequently it can lead to urethral strictures.

Sexual physiology
The male urethra is the conduit for sperm during sexual intercourse. It also serves as a passage for urine to flow.