vomiting, ejection of food and other matter from the stomach through the mouth, often preceded by nausea. The process is initiated by stimulation of the vomiting center of the brain by nerve impulses from the gastrointestinal tract or other part of the body. The vomiting center then sends out nerve impulses that precipitate spasmodic muscular contractions of the stomach wall and downward spasms of the diaphragm. The pressure generated then forces up the contents of the stomach. The vomiting mechanism may be in response to local irritation (diseases or disorders of the gastrointestinal tract, overburdening of the capacity and digestive capabilities of the stomach, ingestion of harmful foods or substances) or result from a metabolic disturbance (as in pregnancy) or from disorders or stimulation of the nervous system (e.g., migraine, motion sickness, infectious disease, brain tumor or injury, disagreeable odors). Vomiting may also be a reflex action to other spasmodic conditions (whooping cough, gagging).

Forcible ejection of the stomach contents from the mouth, usually following nausea. Causes include illness, motion sickness, certain drugs, inner ear disorders, and head injury. Vomiting may occur without nausea (e.g., after extreme exertion). Two centres in the brain's medulla oblongata are believed to control it; the vomiting centre initiates and controls a series of muscle contractions beginning at the small intestine and moving through the stomach and esophagus. This reaction may be set off by the chemoreceptor trigger zone, stimulated by many toxins and drugs, to rid the body of them, or by stimuli from various parts of the body that may be stressed or diseased. Severe vomiting may cause dehydration, malnutrition, or esophageal wall rupture. Vomiting of blood may be a sign of bleeding ulcer or other upper digestive tract disorders. Seealso bulimia.

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Vomiting (also called throwing up, emesis) is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose. Undesired vomiting may result from many causes, ranging from gastritis or poisoning to brain tumors, or elevated intracranial pressure. The feeling that one is about to vomit is called nausea. It usually precedes, but does not always lead to vomiting. Antiemetics are sometimes necessary to suppress nausea and vomiting, and, in severe cases where dehydration develops, intravenous fluid may need to be administered to replace fluid volume.

Vomiting is different from regurgitation, although the two terms are often used interchangeably. Regurgitation is the return of undigested food (that has not yet reached the stomach) back up the esophagus to the mouth. The causes of vomiting and regurgitation are generally different.

Mechanism

Vomiting center

Vomiting is coordinated in the vomiting center in the lateral medullary reticular formation in the pons. 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.

There are various sources of input to the vomiting center:

• The chemoreceptor trigger zone at the base of the fourth ventricle has numerous dopamine D₂ receptors, serotonin 5-HT₃ receptors, opioid receptors, Acetylcholine receptors (which can bind nicotine), and receptors for substance P. Stimulation of different receptors are involved in different pathways leading to emesis, in the final common pathway substance P appears to be involved.
• The vestibular system which sends information to the brain via cranial nerve VIII (vestibulocochlear nerve). It plays a major role in motion sickness and is rich in muscarinic receptors and histamine H₁ receptors.
• Cranial nerve X (vagus nerve), which is activated when the pharynx is irritated, leading to a gag reflex.
• Vagal and enteric nervous system inputs that transmit information regarding the state of the gastrointestinal system. Irritation of the GI mucosa by chemotherapy, radiation, distention, or acute infectious gastroenteritis activates the 5-HT₃ receptors of these inputs.
• The CNS mediates vomiting arising from psychiatric disorders and stress from higher brain centers.

Vomiting act

The vomiting act encompasses three types of outputs initiated by the chemoreceptor trigger zone: Motor, parasympathetic nervous system (PNS), and sympathetic nervous system (SNS). They are as follows:

• Increased salivation to protect the enamel of teeth from stomach acids (excessive vomiting leads to dental erosion). This is part of the PNS output.
• A deep breath is taken to avoid aspiration of vomit.
• Retroperistalsis, starting from the middle of the small intestine, sweeping up the contents of the digestive tract into the stomach, through the relaxed pyloric sphincter.
• A lowering of intrathoracic pressure (by inspiration against a closed glottis), coupled with an increase in abdominal pressure as the abdominal muscles contract, propels stomach contents into the esophagus as the lower esophageal sphincter relaxes. The stomach itself does not contract in the process of vomiting except for at the annular notch, nor is there any retroperistalsis in the esophagus.
• Vomiting is ordinarily preceded by retching.
• Vomiting also initiates an SNS response causing both sweating and increased heart rate.

The neurotransmitters that regulate vomiting are poorly understood, but inhibitors of dopamine, histamine, and serotonin are all used to suppress vomiting, suggesting that these play a role in the initiation or maintenance of a vomiting cycle. Vasopressin and neurokinin may also participate.

Content

Gastric secretions and likewise vomit are highly acidic. Recent food intake will be reflected in the gastric vomit. Irrespective of the content, vomit tends to be malodorous.

The content of the vomitus (vomit) may be of medical interest. Fresh blood in the vomit is termed hematemesis ("blood vomiting"). Altered blood bears resemblance to coffee grounds (as the iron in the blood is oxidized) and, when this matter is identified, the term "coffee ground vomiting" is used. Bile can enter the vomit during subsequent heaves due to duodenal contraction if the vomiting is severe. Fecal vomiting is often a consequence of intestinal obstruction or a gastrocolic fistula and is treated as a warning sign of this potentially serious problem ("signum mali ominis"); such vomiting is sometimes called "miserere."

If the vomiting reflex continues for an extended period with no appreciable vomitus, the condition is known as non-productive emesis or dry heaves, which can be painful and debilitating.

Complications

Aspiration of vomit

Vomiting can be dangerous if the gastric content gets into the respiratory tract. Under normal circumstances the gag reflex and coughing will prevent this from occurring, however these protective reflexes are compromised in persons under the influences of certain substances such as alcohol or anesthesia. The individual may choke and asphyxiate or suffer an aspiration pneumonia.

Dehydration and electrolyte imbalance

Prolonged and excessive vomiting will deplete the body of water (dehydration) and may alter the electrolyte status. Gastric vomiting leads to the loss of acid (protons) and chlorine leads to hypochloremic metabolic alkalosis (low chloride levels together with high HCO₃ 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 HCO₃^- which can lead to metabolic acidosis.

Mallory-Weiss tear

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 blood is admixed with vomit after several episodes.

Dental

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

Causes

Vomiting may be due to a large number of causes, and protracted vomiting has a long differential diagnosis.

Digestive tract

Causes in the digestive tract:

• Gastritis (inflammation of the gastric wall, usually by viruses)
• Pyloric stenosis (in babies, this typically causes a very forceful "projectile vomiting" and is an indication for urgent surgery)
• Bowel obstruction
• Acute abdomen and/or peritonitis
• Ileus
• Cholecystitis, pancreatitis, appendicitis, hepatitis
• Food allergies
• In children, it can be caused by an allergic reaction to cow's milk proteins (milk allergy)

Sensory system and brain

Causes in the sensory system:

• Movement: motion sickness (which is caused by overstimulation of the labyrinthine canals of the ear)
• Ménière's diseaseCauses in the brain:
• Concussion
• Cerebral hemorrhage
• Migraine
• Brain tumors, which can cause the chemoreceptors to malfunction
• Benign intracranial hypertension and hydrocephalusMetabolic disturbances (these may irritate both the stomach and the parts of the brain that coordinate vomiting):
• Hypercalcemia (high calcium levels)
• Uremia (urea accumulation, usually due to renal failure)
• Adrenal insufficiency
• HypoglycemiaPregnancy:
• Hyperemesis, Morning sicknessDrug reaction (vomiting may occur as an acute somatic response to):
• alcohol (being sick while being drunk or being sick the next morning, suffering from the after-effects, i.e., the hangover).
• opioids
• selective serotonin reuptake inhibitors
• many chemotherapy drugs
• some entheogens (such as peyote or ayahuasca)Illness:
• Norwalk virus

Other

• Self-induced
• Eating disorders (anorexia nervosa or bulimia nervosa)
• To remove a poison in case such has been ingested (some poisons should not be vomited as they may be more toxic when inhaled or aspirated; it is, in general, considered better to ask for help before inducing vomiting)
• Some people who are engaged in binge drinking will induce vomiting in order to make room in their stomachs for further alcohol consumption. In the United Kingdom, this practice is known as tactical chundering, or hitting the reset button. In the United States, it is known as boot and rally or pulling the trigger.
• After surgery (postoperative nausea and vomiting)
• Disagreeable sights, smells or thoughts (such as decayed matter, others' vomit, thinking of vomiting), etc.
• Extreme pain, such as intense headache or myocardial infarction (heart attack)
• Violent emotions
• Cyclic vomiting syndrome (a poorly-understood condition with attacks of vomiting)
• High doses of ionizing radiation will sometimes trigger a vomit reflex in the victim
• Violent fits of coughing or hiccups
• Nervousness

Unusual types of vomiting

Fecal vomiting or antiperistalsis is a kind of emesis in which fecal matter is expelled from the intestines into the stomach, by spasmodic contractions of the gastric muscles, and then subsequently forcefully expelled from the stomach up into the esophagus and out through the mouth and sometimes nasal passages. Alternative medical terms for fecal vomiting are copremesis and stercoraceous vomiting. It was also referred to as miserere in medieval times.

Related medication

Emetics

An emetic, such as syrup of ipecac, is a substance that induces vomiting when administered orally or by injection. An emetic is used medically where a substance has been ingested and must be expelled from the body immediately. Inducing vomiting can remove the substance before it is absorbed into the body. Ipecac abuse can lead to detrimental health effects.

Antiemetics

An antiemetic is a drug that is effective against vomiting and nausea. Antiemetics are typically used to treat motion sickness and the side-effects of some opioid analgesics and chemotherapy directed against cancer.

Antiemetics act by inhibiting the receptor sites associated with emesis. Hence, anticholinergics, antihistamines, dopamine antagonists, serotonin antagonists, and cannabinoids are used as anti-emetics.

Social implications

Nausea inducement in groups

It is quite common that, when one person vomits, others nearby will become nauseated, particularly when smelling the vomit of others, often to the point of vomiting themselves. It is believed that this is an evolved trait among primates. Many primates in the wild will tend to browse for food in small groups. Should one member of the party react adversely to some ingested food, it may be advantageous (in a survival sense) for other members of the party also to vomit. This tendency in human populations has been observed at drinking parties, where excessive consumption of alcoholic beverages may result in a number of party members vomiting nearly simultaneously, this being triggered by the initial vomiting of a single member of the party. This phenomenon has been touched on in popular culture: Notorious instances appear in the films Monty Python's The Meaning of Life (1983) and Stand By Me (1986), while, in the computer game Theme Hospital, it is referred to as a 'vomit wave' and can spread through the hospital quickly.

Intense vomiting in ayahuasca ceremonies is a common phenomenon. However, people who experience "la purga" after drinking ayahuasca, in general, regard the practice as both a physical and spiritual cleanse and often come to welcome it. It has been suggested that the consistent emetic effects of ayahuasca — in addition to its many other therapeutic properties — was of medicinal benefit to indigenous peoples of the Amazon, in helping to clear parasites from the gastrointestinal system.

There have also been documented cases of a single ill and vomiting individual inadvertently causing others to vomit, when they are especially fearful of also becoming ill, through a form of mass hysteria.

Context

Most people try to contain their vomit by vomiting into a sink, toilet, or trash can, as both the act and the vomit itself are widely considered embarrassing; vomit is also difficult to clean. On airplanes and boats, special bags are supplied for sick passengers to vomit into. A special disposable bag containing absorbent material that solidifies the vomit quickly is available, also, making it convenient and safe to keep (leakproof, puncture-resistant, odorless) until there is an opportunity to dispose of it conveniently.

People who vomit chronically (e.g., as part of an eating disorder such as bulimia nervosa) may devise various ways to hide this disorder.

Sound

According to an online study of 30 traditionally bad sounds, the sound of vomiting is the worst sound in the world. Professor Cox of the University of Salford's Acoustic Research Centre said that "We are pre-programmed to be repulsed by horrible things such as vomiting, as it is fundamental to staying alive to avoid nasty stuff". It is thought that the thought of disgust is triggered by the sound of vomiting to protect food from those possibly diseased nearby.

See also

• Emetophilia
• Emetophobia

References

External links

• Cyclical Vomiting Syndrome