Defecation - physiological act of liberation of the intestine from feces. Defecation is regulated by the Central nervous system and is the result of irritation of sensitive nerve endings of the mucous membrane of the rectum. The stimulation of nerve endings transmitted to the spinal cord, where at the level of the lumbar spine is the center of defecation. From this centre the excitement spread to the brain cortex, causing a specific feeling and the urge to have a bowel movement. But even with the urge to defecate stool held in the rectum due to constant tonic stress two anal sphincter - external and internal. The act of defecation occurs reflex. Irritation of receptors of the wall of the rectal ampulla causes involuntary relaxation its internal sphincter, peristaltic contractions of the muscles in the walls of the colon and rectum. Then there is arbitrary outdoor relaxation of the sphincter of the rectum. Dump the rectum contribute breath, strain the abdominal muscles, the diaphragm and the muscles of the pelvic floor.
With the defeat of a spinal cord (inflammation, trauma, tumors) above the center of defecation interrupted influence coming from the overlying structures of the brain, especially from the bark of the big hemispheres, and defecation becomes spontaneous. Involuntary defecation could come with a strong emotional impact (for example, fear). Some diseases of the gastrointestinal tract (dysentery, tumors, ulcers) can cause disordered defecation, manifested in the form of diarrhea or constipation.