Urethra

The urethra is the tube that carries urine from the bladder to the outside of the body. In males, it also carries semen.

Urinary bladder: A muscular organ that stores urine before it leaves the body. The urethra begins at the bladder, where stored urine enters it.
Micturition reflex: A spinal reflex that coordinates bladder contraction and sphincter relaxation during urination. It initiates urine passage through the urethra when bladder stretch signals become strong.
Female urethra: The short urethra that carries urine from the bladder to an opening in the vulvar vestibule. Its short course distinguishes it from the longer male urethra.
Urethritis: Inflammation of the urethra, commonly caused by infection or irritation. Inflammation can cause pain during urination and urethral discharge.
Urination: The process of emptying urine from the bladder through the urethra. This is the main function shared by urethras in all sexes.
Detrusor muscle: The smooth muscle layer of the bladder wall that contracts to expel urine. Its contraction raises pressure that drives urine into the urethra.
Male urethra: The urethra that passes through the prostate and penis and carries urine and semen at different times. Its route through reproductive structures gives it a second function absent from the female urethra.
Urethral stricture: A narrowing of the urethral lumen, usually caused by scar tissue. Narrowing obstructs urine flow through the urethra.
Internal urethral sphincter: A ring of smooth muscle at the bladder outlet that helps regulate urine flow. It guards the urethral opening from the bladder and helps prevent semen from entering it.
Pelvic floor: A group of muscles and connective tissues that supports pelvic organs and helps control continence. It supports the urethra and contributes to closure and control of urine flow.

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