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Nausea and vomiting are common complaints seen in a variety of settings. The cause may be associated with something as innocuous as spinning too fast on an amusement park ride. It also may be a therapy induced adverse reaction, or a symptom in a much more serious and complicated clinical presentation. Nausea and vomiting may occur independently, but generally they are closely allied and are presumed to be mediated by the same neural pathway, and therefore will be discussed together. Nausea denotes the imminent desire to vomit, usually referred to the throat or epigastrium. Vomiting (or emesis) refers to the forceful oral expulsion of gastric contents. Retching denotes the labored rhythmic contraction of respiratory and abdominal musculature that frequently precedes or accompanies vomiting.(1)
Nausea usually precedes vomiting and is associated with diminished functional activity of the stomach (e.g., hypoperistalsis, hyposecretion, and hypotonicity), and altered activity of the small intestine. Other distressing occurrences include parasympathetic autonomic activities such as increased diaphoresis, hypersalivation, skin pallor, and defecation. Sometimes hypotension and bradycardia (vasovagal syndrome) may be present.
The act of vomiting requires the coordinated contractions of the abdominal muscles, pylorus and antrum, a raised gastric cardia, diminished lower esophageal sphincter pressure, and esophageal dilatation.(2) The stomach itself plays a relatively passive role in emesis, with the major force being provided by the abdominal musculature. Two functionally distinct medullary centers are actually responsible for the act of vomiting. Those centers are the chemoreceptor trigger zone, located in the area postrema of the floor of the fourth ventricle, and the vomiting center, located in the dorsal portion of the lateral reticular formation.
The vomiting center is located in close proximity to other medullary centers, which regulate respiration, vasomotor, and other autonomic functions that may play a role in vomiting. It is the vomiting center that actually controls and integrates the act of vomiting. It receives afferent stimuli from the gastrointestinal tract and other parts of the body, from higher brainstem and cortical centers, especially the labyrinthine apparatus, and from the chemoreceptor trigger zone.(1) When excited, afferent impulses are integrated by the vomiting center, resulting in efferent impulses to the salivation center, respiratory center, and the pharyngeal, GI, and abdominal muscles, leading to vomiting.(3) The chemoreceptor trigger zone by itself cannot mediate the act of vomiting. However, impulses are sent from this area to the vomiting center, which initiates emesis. The chemoreceptor trigger zone is usually associated with chemically induced vomiting, and can be activated by a number of different drugs, as well as other stimuli such as bacterial toxins, radiation, and metabolic abnormalities that occur with uremia and hypoxia. Similarly, the vomiting associated with pregnancy is probably initiated through the chemoreceptor trigger zone. Vomiting should be distinguished from regurgitation, which refers to the expulsion of food in the absence of nausea, and without the abdominal diaphragmatic muscular contractions associated with vomiting. Regurgitation may occur, for example, as a result of pressure differences caused from an incompetent lower esophageal sphincter, seen in gastroesophageal reflux disease, or from pyloric spasm or obstruction seen in peptic ulcer disease.
Nausea and vomiting are associated with many organic and functional disorders. Many acute abdominal emergencies such as acute appendicitis, acute cholecystitis, intestinal obstruction, or peritonitis may be associated with nausea and vomiting, as well as other disorders of the alimentary tract. Viral, bacteria
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