Elderly don t have the lymphatics we have they can t prevent peripheral edema while they are up. When they lie down venous and lymphatic return from the lower extremities increase. Thus, urination is necessary. She referenced the section on physiology of micturition in our text and said we should get a copy this.
Micturition is complex requiring control from the cerebral cortex, spinal cord and plexuses.
This is why we give BPH patients alpha blockers to relax the sphincter. For micturition to occur, the urethral sphincter under alpha adrenergic control must relax, and the detrusor muscle under parasympathetic control must contract. She recommends thinking about the fight or flight phenomena. In times of danger, the sympathetics take over allowing for bladder relaxation and tightening of the external urethral sphincter. Micturiion occurs when the parasympathetics take over.