4. Prevention of Autonomic Hyperreflexia Autonomic hyperreflexia is a symptom of injury in the fifth and sixth thoracic spinal cord segments. In this condition, because of some stimuli or accumulated urine and stool, high blood pressure, headache, sweating, horripilation, tightness in the chest, and other symptoms may occur. Stool removal can alleviate some of these symptoms.
4 Chapter 2. Structure of the Intestine and the Mechanism of Defecation 1. Structure of the Intestine nutritionFigure 1 shows the structure of the intestine. 2. Mechanism of Defecation Food is digested in the stomach and absorbed in the small intestine, and then transferred together with fluids to the large intestine to produce solid stool. When the stool moves from the colon to the rectum, the rectal wall is stimulated. Then, the stimulation signal is transferred to the cerebrum, causing the urge to defecate. The internal anal sphincter reflexively relaxes in response to the defecation urge, and the internal anal pressure increases. Then, the external anal sphincter relaxes to push out the stool from the anus. The movement of the intestine is paralyzed immediately after spinal cord injury, and the intestine gradually recovers to release gases. In general, it is considered that the normal functions of the enteric nervous system are maintained in the chronic phase of injury. In the case of sacral spinal cord injury, the colon relaxes and the reflex movement of the intestinal reflex does not exist, resulting in constipation, which might cause incontinence. In the case of spinal injury above the sacral cord, the colon and anus are subjected to excessive muscle tone, referred to as spasticity, and therefore, the external anal sphincter cannot be controlled voluntarily and is kept firmly contracted. Intestinal movement that allows movement of the stool to the anus decreases, and therefore, the stool accumulates in the colon. Rectal relaxation, however, relaxes the internal anal sphincter, and simultaneously, defecation reflex is triggered. Therefore, cathartic drugs and stimuli are effective in promoting defecation. In addition, Stomach Descending colon Sigmoid colon Duodenum Transverse colon Ascending colon Cecum Rectum Figure 1. Intestinal structures involved in defecation
sensation in the anal mucosa is reduced or numbed in the case of spinal cord injury. In the case of injury above the eighth thoracic spinal cord, loss of abdominal muscle straining can cause constipation.