Vomiting

Vomiting  (also throwing up or emesis) is the forceful expulsion of the contents of one's stomach through the mouth. Vomiting may result from many causes, ranging from gastritis or poisoning to brain tumors, or elevated intracranial pressure (ICP). The feeling that one is about to vomit is called nausea. It usually precedes vomiting, but it 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.

The medical branch investigating vomiting, emetics and antiemetics is called emetology.

Vomiting center
Vomiting is coordinated in the vomiting center in the lateral medullary reticular formation in the medulla. Receptors on the floor of the fourth ventricle of the brain represent a chemoreceptor trigger zone, stimulation of which can lead to vomiting. The chemoreceptor zone lies outside the blood-brain barrier, and 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, 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.

Vomiting act
The vomiting act encompasses three types of outputs initiated by the medulla: Motor, parasympathetic nervous system (PNS) and sympathetic nervous system (SNS). Collectively, they are as follows:


 * Increased salivation to protect the enamel of teeth from stomach acids (excessive vomiting leads to caries). This is part of the PNS output.
 * 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 without involvement of retroperistalsis. The lower esophageal sphincter relaxes. This is part of the motor output, and it is also important to note that the stomach itself does not contract in the process of vomiting.
 * Vomiting is ordinarily preceded by retching.
 * Vomiting also initiates a 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
Since the stomach secretes acid, vomit contains a high concentration of hydronium ions and is thus strongly acidic. Recent food intake will be reflected in the gastric vomit.

The content of the vomitus (vomit) may be of medical interest. Fresh blood in the vomit is termed hematemesis ("blood vomiting"). Old 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, and is treated as a warning sign of this potentially serious problem ("signum mali ominis"); such vomiting is sometimes called "miserere". If food has recently been consumed, then partly digested food may show up in the vomit.

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

Aspiration of vomitus
Vomiting can be very 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 narcotic influences 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. The loss of acids leads to metabolic alkalosis (increased blood pH), and the electrolyte imbalance shows hypokalemia (potassium depletion) and hypochloremia (chlorine 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 will become cachectic.

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
 * 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 disease

Causes in the brain:
 * Concussion
 * Cerebral hemorrhage
 * Migraine
 * Brain tumors
 * Benign intracranial hypertension and hydrocephalus

Metabolic 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
 * Hypoglycemia

Pregnancy:
 * Hyperemesis, Morning sickness

Drug reaction (vomiting may occur as an acute somatic response to):
 * alcohol (being sick whilst 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)

Other

 * Self-induced
 * Eating disorders (anorexia nervosa or bulimia nervosa)
 * One other way is when one is feeling nauseated actually thinking repeatedly and continuously of vomiting can cause a person to do so.
 * Sexual fetish (emetophilia)
 * 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 generally 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, and as boot and rally or pulling the trigger in the United States.
 * After surgery (postoperative nausea and vomiting)
 * Disagreeable sights or smells, such as decayed matter, others' vomit, etc.
 * Extreme pain, such as intense headache or myocardial infarction (heart attack)
 * Violent emotions (including laughing)
 * 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
 * Nervousness

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.

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 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 generally regard it 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 do so, 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. Alternatively, a special disposable bag is available containing absorbent material that solidifies the vomit quickly, 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.

In language
As with other physiological processes involving body wastes, vomiting has taboo aspects. This is shown by the large number of colourful euphemisms and dysphemisms for vomiting. (see: toilet humour). Reference to vomiting is often made in speech (e.g. "it makes me sick", "I need a bucket") or by gesturing to signify being disgusted by someone or something.

Slang terms for the act of vomiting include: "hurling", "throwing up", "upchucking", "booting", "puking", "ralphing", "barfing", "keeling", "chucking up", "sicking up", "tossing your cookies", "shouting groceries", "spewing", "spewing chunks", "chundering" and "boking".

"Wallace and Gromit" has recently become rhyming slang for vomit.

"Puke" and "puking" date from at least the 16th century. In As You Like It, Shakespeare talks of the infant 'Mewling and puking in the nurse's arms'.

In other animals

 * Whales vomit regularly (every 7 to 10 days) as a means of the ordinary digestive process, to expel indigestible items they have swallowed.
 * The domestic cat is well known for its tendency to vomit, particularly when attempting to dislodge hairballs from its throat or upper gastrointestinal tract. Chronic vomiting in cats may indicate underlying thyroid, liver or kidney dysfunction and should be investigated by a veterinarian.  Dogs also vomit often (frequently after eating grass) and are also known for eating their own vomit, a fact even cited in the Bible: KJV Proverbs 26:11 "As a dog returneth to his vomit, so a fool returneth to his folly."
 * Owls will expel the undigestible bones and fur of their meals as a pellet after partial digestion of the nutritious parts rather than passing them through the digestive tract.
 * Some adult birds regurgitate food to feed their young, triggered by a feather or a beak of their young. The food can be either incompletely digested or partially predigested, depending on the species. Some bird species may also use regurgitation as a form of defense, vomiting when wounded or molested. When an intruder or a predator comes near a fulmar on its nest, the bird vomits oil up to 3 feet at the enemy. Larger animals, such as wolves, may also regurgitate partially or undigested food to feed their young.
 * When in danger, the sea cucumber may eject its entire digestive tract. The animal is able to re-grow another one.
 * Some large mammals, including horses, cannot or rarely vomit.
 * Many rodents are readily killed by commercial poisons because they lack the ability to vomit, which can be problematic for some pet owners.