Urethra actively opens from the very beginning of micturition: a new concept of urethral function.

Transvaginal or transrectal ultrasound was carried out in an adult female and a male volunteer during micturition. Although the male urethra was enclosed by the prostate, its construction and the function were almost identical to the female urethra. The anterior fibromuscular stroma was not a part of the prostate, but was a part of the urethral muscle. The urethra was surrounded by a thick single muscle unit, developed only on the anterior and lateral sides of the urethra. When the participant wished to urinate, the initial motion was not a bladder contraction, but an active opening of the urethral lumen by the muscle unit. The same unit closed the urethra when continence was kept. In conclusion, the main function of the urethra is thought to be not a closure, but an opening to control the entire micturition process, rather than the bladder being primarily responsible for the control of micturition.