The feeling of nausea, and an array of sympathetic and parasympathetic responses initiate vomiting or emesis. Sympathetic responses include sweating, pallor, increased respiration and heart rate and dilatation of pupils. Parasympathetic responses include profuse salivation, pronounced motility of the oesophagus, stomach, and duodenum, relaxation of the oesophageal sphincters. Duodenal contents can be forced into the stomach by anti-peristalsis (Pic.). During the expulsion of gastric contents, the person takes a deep breath, the pylorus is closed, the glottis is closed so respiration stops, and the stomach is squeezed between the diaphragm and the abdominal muscles, causing rapid emptying (Pic). Vomiting is co-ordinated by the vomiting centre in the medulla.
Tue, 2007-06-19 11:45