Vomiting begins when a stimulus activates central or peripheral vomiting pathways. The final event is a coordinated motor response: gastric relaxation, retrograde movement of intestinal or gastric contents, closure of the glottis, contraction of abdominal muscles and diaphragm, and expulsion of contents. In infectious gastroenteritis, pathogens irritate the intestinal mucosa, alter absorption and secretion, and stimulate vagal afferents. Vomiting may occur with diarrhea, abdominal cramps, fever, and dehydration. Norovirus commonly causes vomiting and diarrhea, and fluid replacement is central to preventing dehydration. In obstruction, vomiting occurs because intestinal contents cannot move forward. Proximal obstruction may cause early, frequent vomiting. Distal obstruction may cause abdominal distention, crampy pain, obstipation, and feculent or bilious emesis. Merck/MSD lists bowel obstruction as a cause associated with distention, obstipation, tympany, bilious vomiting, prior abdominal surgery, or hernia. In increased intracranial pressure, vomiting may occur without nausea and can be associated with headache, neurologic deficits, papilledema, altered mental status, or morning predominance. In metabolic illness, vomiting may result from acidosis, electrolyte derangement, uremia, adrenal crisis, hypercalcemia, hyponatremia, diabetic ketoacidosis, or severe infection. In pregnancy, nausea and...