Increasing stimulation of the parasympathetic nervous system decreases heart rate and blood pressure as well as the size of the pupil. At the same time, it increases digestion, urination, defecation and sexual arousal. The parasympathetic nervous system governs activities that involve relaxation.
The parasympathetic nervous system controls body functions that do not require immediate action. These include digestion and sexual arousal. It also promotes urination by moving urine down the tubes that connect the kidneys to the bladder, and causes the bladder to contract and relaxes the sphincter that allows urination. Defecation is aided by the movement of feces along the intestine and relaxation of the anal sphincter. Sexual arousal is dependent on the engorgement of sexual organs by blood, and stimulation of the PNS allows this to occur. In the female, PSN stimulation assists the movement of eggs from the fallopian tube to the uterus.
The PSN increases secretions, such as saliva, and this aids digestion. Mucous production is increased while the muscles of respiration relax.
Stimulation of the PSN decreases heart rate. It decreases blood pressure by causing dilation of the blood vessels. This is often seen in athletes who have a low resting heart rate and a fast recovery time. Runners and bicyclists are good examples of this.