The urethra is a narrow, muscular tube that is responsible for urine — and, in males, semen — from the bladder or ejaculatory ducts to the exterior of the body. The urethra is made up of a series of tissues, including prostatic, membranous, and spongy heterogenous segments. The urethra begins at the bladder and extends through the pelvic and urogenital diaphragms.
The urethra is the tube that allows urine to pass from the bladder to outside the body. For people with testes, the urethra is also the tube that allows semen to pass during ejaculation. When the penis is erect, the flow of urine is temporarily blocked from the urethra, which means only semen is ejaculated during orgasm.
Since the urethra transports semen outside of the body — and semen needs to be carried outside of the body in order to fertilize an egg — a healthy and well-functioning urethra plays an important role in male fertility. If the urethra experiences inflammation, infection, weakening, narrowing, or any type of discomfort, that can negatively affect fertility.
Urethritis is an infection or inflammation of the urethra. It can occur in the case of a bacterial or viral infection, especially a sexually transmitted infection, or because of trauma or an allergic reaction.
It's possible to develop urethral strictures, when the urethra narrows and causes difficulty, discomfort, or even pain when urinating. Since semen also passes through the urethra, it's possible for a stricture to even block some or all of the semen from passing out the body during orgasm.
Urethral strictures can be caused by scar tissue that develops from a sexually transmitted disease or infection, other inflammatory infections, injury or trauma to genitalia, or from unintentional damage by catheters or other surgical instruments.
Urethral structures do not heal on their own and are more likely to worsen over time. If a person experiences symptoms like pain during urination, a slower or weaker than usual stream of urine, the inability to empty the bladder, straining when urinating, or the increased urge to urinate, they should see a doctor. Left untreated, a urethral stricture can lead to bladder and kidney damage, infections, and even infertility.