Nausea and Vomiting

Vomiting, or emesis, is the forceful retrograde expulsion of gastric contents from the body. Nausea is the unpleasant sensation that precedes vomiting. Nausea frequently is relieved by vomiting and may be accompanied by increased parasympathetic nervous system activity including diaphoresis, salivation, bradycardia, pallor, and decreased respiratory rate. Retching ("dry heaves") is the simultaneous contraction of the abdominal muscles and muscles of inspiration that may occur with vomiting.

Vomiting should be differentiated from regurgitation, the nonforceful expulsion of gastric contents into the esophagus, and eructation (belching), the expulsion of swallowed gastric air. Regurgitation or eructation may be volitional, or result from an incompetent lower esophageal sphincter. Anatomic alterations of the esophagus (by mucosal rings, carcinoma, or diverticula) and disorders of esophageal motility (such as achalasia and diffuse spasm) may simulate vomiting, but the food bolus never reaches the stomach.