vomiting, ejection of food and other matter from the stomach through the mouth, often preceded by nausea. The process is initiated by stimulation of the vomiting center of the brain by nerve impulses from the gastrointestinal tract or other part of the body. The vomiting center then sends out nerve impulses that precipitate spasmodic muscular contractions of the stomach wall and downward spasms of the diaphragm. The pressure generated then forces up the contents of the stomach. The vomiting mechanism may be in response to local irritation (diseases or disorders of the gastrointestinal tract, overburdening of the capacity and digestive capabilities of the stomach, ingestion of harmful foods or substances) or result from a metabolic disturbance (as in pregnancy) or from disorders or stimulation of the nervous system (e.g., migraine, motion sickness, infectious disease, brain tumor or injury, disagreeable odors). Vomiting may also be a reflex action to other spasmodic conditions (whooping cough, gagging).