VOMITING

also called Emesis, the forcible ejection of the stomach contents from the mouth. Like nausea, vomiting may have a wide range of causes, including motion sickness, the use of certain drugs (recreational, illegal, and prescription), intestinal obstruction, disease or disorder of the inner ear, injury to the head, and appendicitis. It may even occur without nausea, such as after extreme physical exertion. Vomiting is believed to be controlled by two distinct brain centres-the vomiting centre and the chemoreceptor trigger zone-both located in the medulla oblongata. The vomiting centre initiates and controls the act of emesis, which involves a series of contractions of the smooth muscles lining the digestive tract. These contractions begin at the small intestine and move successively through the stomach and the esophagus until the contents of the stomach are forced out the mouth. The vomiting centre responds directly to stimuli from various parts of the body that may be stressed or diseased. The chemoreceptor trigger zone, by contrast, is stimulated by many toxins and drugs. Activation of this brain region stimulates in turn the vomiting centre, which initiates emesis in an effort to rid the body of the toxin. In severe cases vomiting may result in dehydration, malnutrition, or rupturing of the esophageal wall.