Vomiting

Vomiting is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose. Vomiting can be caused by a wide variety of conditions; it may present as a specific response to ailments like gastritis or poisoning, or as a non-specific sequela ranging from brain tumors and elevated intracranial pressure to overexposure to ionizing radiation. The feeling that one is about to vomit is called nausea; it often precedes, but does not always lead to, vomiting. Antiemetics are sometimes necessary to suppress nausea and vomiting. In severe cases, where dehydration develops, intravenous fluid may be required. Self-induced vomiting can be a component of an eating disorder such as bulimia, and is itself now an eating disorder on its own, purging disorder. Vomiting is different from regurgitation, though the terms are often used interchangeably. Regurgitation is the return of undigested food back up the esophagus to the mouth, without the force and displeasure associated with vomiting. The causes of vomiting and regurgitation are generally different. Vomiting is dangerous if gastric content enters the respiratory tract. Under normal circumstances the gag reflex and coughing prevent this from occurring; however, these protective reflexes are compromised in persons under the influence of certain substances (including alcohol) or even mildly anesthetized. The individual may choke and asphyxiate or suffer aspiration pneumonia. Prolonged and excessive vomiting depletes the body of water (dehydration), and may alter the electrolyte status. Gastric vomiting leads to the loss of acid (protons) and chloride directly. Combined with the resulting alkaline tide, this leads to hypochloremic metabolic alkalosis (low chloride levels together with high HCO−3 and CO2 and increased blood pH) and often hypokalemia (potassium depletion). The hypokalemia is an indirect result of the kidney compensating for the loss of acid. With the loss of intake of food the individual may eventually become cachectic. A less frequent occurrence results from a vomiting of intestinal contents, including bile acids and HCO−3, which can cause metabolic acidosis. Repeated or profuse vomiting may cause erosions to the esophagus or small tears in the esophageal mucosa (Mallory–Weiss tear). This may become apparent if fresh red blood is mixed with vomit after several episodes. Recurrent vomiting, such as observed in bulimia nervosa, may lead to destruction of the tooth enamel due to the acidity of the vomit. Digestive enzymes can also have a negative effect on oral health, by degrading the tissue of the gums. Receptors on the floor of the fourth ventricle of the brain represent a chemoreceptor trigger zone, known as the area postrema, stimulation of which can lead to vomiting. The area postrema is a circumventricular organ and as such lies outside the blood–brain barrier; it can therefore be stimulated by blood-borne drugs that can stimulate vomiting or inhibit it.