Vomiting is a primary defense reflex that occurs by contraction of diaphragm and relaxation of esophageal sphincters. The process leads to increased gastric pressure and expulsion of its content through the esophagus, pharynx and oral cavity. Laryngeal flap is reflexively closed to prevent aspiration.
Vomiting is controlled by a brain center located in basis of the fourth brain ventricle. The center monitors and evaluates information about distention of digestive tract, serum levels of various substances and has a close relation with vestibular system in inner ear (center of balance and movement). The “vomit-inducing center” is also closely related to brain centers responsible for emotions and psyche.
Digestive tract distension
Distension of digestive tract causes irritation of vagus nerve and this affects the brain center. Distended digestive tract quite logically forces brain to reduce food intake and this is related to feeling of nausea and loss of appetite. If this does not solve the condition, vomit-inducing center gets irritated and vomiting reflex starts. Vomiting should relive the digestive tube by removing its content. This can happen in overeating (stomach dilation) and in cases of intestinal obstruction (ileus) caused by ingested foreign objects, congenital malformations of the digestive tract, digestive tract tumors, post-inflammatory narrowing, etc.
Digestive tract inflammation
Infectious inflammation of stomach may lead to vomiting. Infection-induced vomiting is usually accompanied by diarrhea and does not last for a long time. It can be dangerous in small children and the elderly where it can cause dehydration. Likewise, vomiting may occur in inflammation of other organs like hepatitis, acute pancreatitis and cholecystitis.
Vestibular system irritation
This pair organ consisting of three semicircular canals is located deep in the skull within the inner ear. It allows us to orient in three-dimensional space and keep balance. Irritation or damage to this organ leads to dizziness, nausea and vomiting. Most simple and banal situation is motion sickness. In the elderly the irritation of vestibular system is caused by Meniere's disease. Alcohol also has direct effect on vestibular tract.
Effect of chemical substances
Many ingested or intravenously administered chemical compounds including toxins, medications and drugs can cause nausea and vomiting. Similar symptoms may be associated with withdrawal symptoms after sudden discontinuation of some of these substances. Quite specific is the effect of alcohol. Alcohol and its metabolites have a direct effect on the vomit-inducing center and also on vestibular system in inner ear (center of balance and movement). Vomiting usually accompanies administration of the majority of chemotherapeutical agents used in treatment of cancer.
Vomiting is typical in conditions with intracranial hypertension (i.e. increased pressure within the skull) such as hemorrhage, cerebral edema in brain tumors, after severe head injuries, etc. Vomiting may accompany infections of the brain tissue (encephalitis) or brain meninges (meningitis). However, the most frequent brain disorder leading to vomiting is relatively trivial brain concussion.
Note: Intracranial hypertension is characterized by sudden vomiting without present nausea.
Disorders of inner environment
Significant imbalance of concentration of essential minerals and ions may lead to nausea and vomiting. This includes the accumulation of pollutants in liver failure or kidney failure (acute and chronic).
Hormonal changes during pregnancy may cause typical morning nausea followed by vomiting.
Acute and short-term vomiting is typical for acute gastroenteritis, alcohol excess and motion sickness. Regular nausea and vomiting in women of fertile age can lead to suspicion of pregnancy; prolonged vomiting in the elderly may be caused by disruption of the inner environment. In physical examination it is important to focus on abdomen and rule out symptoms of acute abdomen (pain palpation, stiff abdomen, absent peristalsis, etc.). Blood tests are important to evaluate mineral and ions concentration, liver tests and renal parameters. Vomiting of uncertain origin or vomiting with present neurological symptoms should be examined by computed tomography of the brain and neurological examination.
Quite special issue is vomiting as a part of intestinal obstruction. This group of pathological conditions is further examined and treated mainly by surgeons.
If it is possible we should treat the underlying cause and prevent dehydration (usually by intravenous infusions) of the patient. Vomiting itself is treatable by drugs known as antiemetics. These drugs inhibit various cell receptors required for transmission of signals to the brain vomit-inducing center and so suppress the vomiting reflex.