Some anatomic factors having to do with urinary continence.

Abstract

AbstractThe levator ani acts synergistically with the sphincter urethrae in the voluntary control of micturition by stretching the urethra and thus narrowing its lumen. Further, because of the high origin of its anterior fibers it pulls the trigonal area of the bladder forward and angulates the urethra. The urogenital diaphragm also is pulled upward and made more horizontal. The concept that the levator compresses the urethra against the symphysis is not valid.The fibers of the urethral sphincter decussate around the urethra but few if any completely encircle it, even in the male. When it contracts it elevates the perineum slightly but its principal function is to convert the urethral configuration into a horizontal slit. In the male the sphincter conforms somewhat to the apex of the prostate so that it is concave as seen from above and is not the strictly horizontal structure so often portrayed. An internal urethral sphincter is present and may be well defined.The visceral pelvic fascia, in particular the anterior component of the uterovaginal fascia, which is the pubocervical fascia of the gynecologist, has much smooth muscle in it. This muscle, acting in line with the pelvic axis, would not elevate the trigonal area or the urethrovesical junction but would exert traction on the urethra, narrowing its lumen. It would thus help maintain involuntary control.The nerve supply of the above structures is considered briefly.