Worlds of David Darling
Encyclopedia of Science
Home > Encyclopedia of Science


Involuntary forcible expulsion of stomach contents through the mouth. It occurs by reverse peristalsis after closure of the pyloric sphincter and opening of the esophago-gastric junction. Vomiting is usually preceded by nausea, pallor, sweating, excessive salivation, and slowing of the heart-rate.

Mechanism of vomiting

Vomiting occurs when the vomiting center in the brainstem is activated. Activation of the center may occur as a result of information passing directly to it from the the frontal lobes of the brain, the digestive tract, or the balancing mechanism in the inner ear when these mechanisms are either damaged or disturbed. The center may also be activated by the chemoreceptor trigger zone, also in the brainstem, which is itself stimulated by the presence in the blood of poisons or certain other substances.

Once activated, the vomiting center sends messages to the diaphragm (the sheet of muscle separating the chest from the abdomen), which presses sharply downward on the stomach, and to the wall of the abdomen, which presses inward. Simultaneously, the pyloric sphincter between the base of the stomach and the small intestine closes and the region between the stomach and the esophagus relaxes. As a result, the stomach contents are expelled upward through the esophagus. As the happens, the larynx (voice-box) is tightly closed by the epiglottis (the flap of cartilage at its entrance) to prevent vomit from entering the trachea (windpipe) and causing choking.

Causes of vomiting

Vomiting commonly happens after overindulgence in food or alcohol. It is also a common adverse effect of many drugs and often follows general anesthesia.

Vomiting may also result from disorders of the stomach or intestine that result in inflammation, irritation, or distension (swelling) of either organ. Such disorders include peptic ulcer, acute appendicitis, gastroenteritis, and food poisoning. Less commonly, vomiting is a symptom of intestinal obstruction due to pyloric stenosis, intussusception, or a tumor of the digestive tract.

Vomiting may also be caused by inflammation of organs associated with the digestive tract, such as the liver (see hepatitis), pancreas, and the gallbladder.

Another possible cause of vomiting is raised pressure within the skull, which may be due to encephalitis, a brain tumor, or a head injury. When the rise is rapid, it causes sudden, extremely forceful vomiting, often without any prior nausea. Vomiting is a common feature of migraine.

Vomiting is also a common feature of disorders affecting the balancing mechanism within the inner ear, such as Ménière's disease and acute labyrinthitis, or of the disturbance of mechanism by unusual movement, such as that experienced on a boat.

Disorders of the endocrine system, such as Addison's disease, may cause vomiting, as do disturbances of hormone production in early pregnancy.

Vomiting is sometimes a symptom of a metabolic disorder, such as ketoacidosis (excessive production of ketones and acids), which may be due to poorly controlled diabetes mellitus.

Internal bleeding from the esophagus, stomach, or duodenum, or swallowing blood from a nosebleed, can also result in vomiting blood.

Vomiting sometimes occurs as a reaction of disgust to a situation or food. It may also be a symptom of a psychological or emotional problem or be part of the psychiatric disorders anorexia nervosa or bulimia.

Investigation and treatment

Persistent vomiting requires investigation by a doctor. Treatment depends on the underlying cause. Food, drink, or any unnecessary medication should not be taken during the active phase of vomiting. Antiemetic drugs may be prescribed.

Related category