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Definition of the Complaint

Vomiting is defined as the forceful contraction of abdominal muscles and the diaphragm in a coordinated fashion expelling the gastric contents through an open gastric cardia into the esophagus and out through the mouth. The medullary vomiting center coordinates this process of vomiting via efferent pathways of the vagus and phrenic nerves. Stimulation of the medullary vomiting center occurs either directly or through the chemoreceptor trigger zone. Direct stimulation may occur through afferent vagal signals from the gastrointestinal tract or other sites including but not limited to the vestibular system, the cerebral cortex, or the hypothalamus. The chemoreceptor trigger zone in the area postrema of the fourth ventricle can be activated by noxious sights and smells or by chemical stimuli in the blood secondary to medications, metabolic abnormalities, and certain toxins.

Gastroesophageal reflux is not vomiting but rather regurgitation, and despite being projectile at times, is an effortless return of gastric contents into the mouth without nausea or coordinated muscular contractions.

Complaints by Cause and Frequency

It is important to remember that vomiting is not a diagnosis but rather a symptom of an underlying pathologic process that requires a thorough evaluation. The causes of vomiting can be grouped based on age of presentation (Table 3-1) or etiology (Table 3-2).

Table 3-1. Causes of Vomiting and Regurgitation in Childhood by Age.
Table 3-2. Causes of Vomiting and Regurgitation in Childhood by Etiology.

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