vomiting

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).

Vomiting

 

a complex reflex action, during which the stomach contents are involuntarily expulsed through the mouth as a result of the excitation of the vomiting center, located in the medulla oblongata.

During vomiting, the pylorus undergoes a spasm and the cardia of the stomach opens. As a result of antiperistaltic contractions, food travels from the stomach to the esophagus and is expulsed to the outside by the spasmodic and jerky contraction of the respiratory musculature and muscles of the anterior abdominal wall. At the same time, the larynx rises and the epiglottis falls, which causes the glottis to close, thus preventing the vomit from entering the respiratory tract. The vomit is hindered from entering the nasal cavity by the raised soft palate.

Vomiting may be provoked by irritants acting on gastric mucosa, by the direct effect of toxins on the vomiting center, and by the stimulation of receptors, for example, in diseases of the abdominal organs, the brain, and meninges. Psychogenic and conditioned-reflex vomiting is also possible.

Vomiting is generally a defensive act because it helps remove harmful substances from the stomach. However, frequent vomiting, for example, the indomitable vomiting that occurs during pyloristenosis, may result in dehydration and disturbances of mineral metabolism and acid-base equilibrium.

Vomiting is dangerous during alcoholic intoxication and coma and when a patient is recovering from general anesthesia; atony of the epiglottis and soft palate may permit vomit to enter the nasal cavity and upper respiratory tract, which can cause asphyxia.

Vomiting is a specific symptom of many pathological conditions in such animals as carnivores, omnivores, and ruminants.

V. A. FROLOV