The objective: :To clarify the mechanisms of urinary continence and micturition.
State of the problem: :Based on the assumption that all peristaltic organs obey the same laws we offer a hypothesis of motor function of the lower urinary tract.
Hypothesis: :The pressure on the wall of the empty bladder is equal to intra-abdominal pressure (IAP). During the intake of urine, the pressure in the bladder rises to a threshold level of the first order (TP-1) and remains unchanged to volume 300-400 ml (main volume). In the volume of the more basic the pressure in the bladder is increased to the threshold pressure of the 2nd order (TP-2), which causes relaxation of the internal urethral sphincter (IUS). Urine, penetrating to the neck of bladder, stimulates the urge to urinate. At this moment, retention of urine is provided by the contraction of the external urethral sphincter (EUS) and puborectal muscle (PRM). If the implementation of urination is not possible, detrusor relaxes adapting to the new volume and intravesical pressure decreases from TP-2 to TP-1, which leads to a reflex contraction of IUS and passive relaxation EUS and PRM. Inflow to the bladder of an additional urine volume causes again an increase in pressure to TP-2, followed by relaxation of IUS and contraction of the EUS and PRM. While the EUS and PRM contract, the IUS relaxes to recover its contractile capacity and vice versa. This ensures continued retention of urine. Urination begins with tension of the abdominal wall, which causes an increase in intra-abdominal pressure and the pressure increase in the bladder from TP-2 to TP-3. All sphincters (IUS, EUS, and PRM) relax, and the urine under the same pressure flows through the urethra opening as the result of coordinated contraction of the bladder micromodules. The maximum volume of urine after a long delay can be up to 1 liter (main and reserve volume, which entered to the bladder as result of the forced delay). In men, when a large amount of urine is accumulated in the bladder, the prostate contraction squeezes the urethral lumen at the level of IUS for supporting of a prolonged urinary retention.
Corresponding Author: LEVIN M.|