Vomiting

Vomiting (or emesis) is the forceful expulsion of the contents of one's stomachthrough the mouth. Although it probably evolved as a mechanism for expelling ingested poisons, vomiting may result from many causes not related to poisoning, ranging from gastritisto brain tumors, or elevated intracranial pressure (ICP). The feeling that one is about to vomit is called nausea. It usually, but not necessarily, precedes vomiting, but it does not always lead to vomiting. Antiemeticsare sometimes necessary to suppress nausea and vomiting.

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

Mechanism

Vomiting is co-ordinated in the vomiting center in the lateral medullary reticular formation in the medulla. Receptors on the floor of the fourth ventricleof 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:

• As stated earlier, the chemoreceptor trigger zone which lies in the fourth ventricle. This area has numerous dopamine D₂ receptors, serotonin 5-HT₃ receptors, and opoid receptors.
• 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 receptorsand 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 systeminputs that transmit information regarding the state of the gastrointestinal system. Irritation of the GI mucosa by chemotherapy, radiation, distention or acute infectious gastroenteritisactivates the 5-HT₃ receptors of these inputs.
• The CNS mediates vomiting arising from psychiatric disorders and stress.

The vomiting act encompasses three types of outputs initiated by the medulla: Motor, ParasympatheticNervous System (PNS) and SympatheticNervous System (SNS). Collectively, they are as follows:

• Increased salivationto protect the enamelof teethfrom stomach acids (excessive vomiting does lead 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 musclescontract, propels stomach contents into the esophaguswithout involvement of retroperistalsis. The lower esophageal sphincterrelaxes. 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. The purpose of retching is to build up the pressure needed to expel the stomach contents from the body. In retching, the body makes movements similar to vomiting. These spasms build up pressure within the chest cavity. When a sufficient amount of pressure has been created, the diaphragm transfers the pressure from the chest to the abdomen, and this pressure then results in actual vomiting.
• Vomiting also initiates a SNS response causing both sweating and increased heart rate.

The neurotransmittersthat regulate vomiting are poorly understood, but inhibitors of dopamine, histamineand serotoninare all used to suppress vomiting, suggesting that these play a role in the initiation or maintenance of a vomiting cycle. Vasopressinand neurokininmay also participate.

Content

As the stomach secretes acid, vomit contains a high concentration of hydronium ionsand is thus strongly acidic. The potential physiological complications associated with excessive vomiting are mainly metabolic alkalosis(increased blood pH), hypokalemia(potassiumdepletion) and hypochloremia(chlorinedepletion). The hypokalemia is an indirect result of the kidneycompensating for the loss of acid.

The content of the vomitus (vomit) may be of medical interest. Fresh bloodin the vomit is termed hematemesis("blood vomiting"). Old blood bears resemblance to coffee grounds (as the ironin the blood is oxidized), and when this matter is identified the term "coffee ground vomiting" is used. Bilecan enter the vomit during subsequent heaves due to duodenalcontraction if the vomiting is severe. Fecal vomitingis 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 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 painful and debilitating.

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 abdomenand/or peritonitis
• Ileus
• Cholecystitis, pancreatitis, appendicitis, hepatitis, pregnancy

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
• Intoxication with alcohol(being sick whilst being drunk or being sick the next morning suffering from the after-effects, i.e. the hangover).
• Cerebral hemorrhage
• Brain tumors
• Benign intracranial hypertensionand hydrocephalus

Metabolic disturbances (these may irritate both the stomach and the parts of the brain that coordinate vomiting):

• Hypercalcemia(high calciumlevels)
• Uremia(ureaaccumulation, usually due to renal failure)
• Adrenal insufficiency
• Hypoglycemia

Opioids, many chemotherapydrugs and a host of other drugs may cause nausea and vomiting.

Other

• Self-induced
  • Eating disorders(anorexia nervosaor bulimia)
  • 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 drinkingwill 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.
• After surgery(postoperative nausea and vomiting)
• Disagreeable sights or smells, such as decayed matter, others' vomit, metal grinding smell, etc.
• Extreme pain, such as intense headacheor myocardial infarction(heart attack)
• Pregnancy (morning sickness, hyperemesis gravidarum)
• Violent emotions (including laughing)
• Cyclic vomiting syndrome(a poorly understood condition with attacks of vomiting)

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 (typically poison) has been ingested and must be expelled from the body immediately. Inducing vomiting can remove the substance before it is absorbed into the body.

Antiemetics

An antiemeticis a drugthat is effective against vomiting and nausea. Antiemetics are typically used to treat motion sicknessand the side effectsof some opioidanalgesicsand chemotherapydirected against cancer.

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 evolvedtrait 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 alcoholicbeverages 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.

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. 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 disordersuch as bulimia nervosa) may devise various ways to hide this abnormality.

In language

As with other physiological processes involving body wastes, vomiting has tabooaspects. This is shown by the large number of colourful euphemismsfor vomiting. (see: toilet humour)

In other animals

• Whalesvomit regularly (every 7 to 10 days) as a means of the ordinary digestive process, to expel inedible things they have swallowed.

• The domestic catis well known for its tendency to vomit, particularly when attempting to dislodge hairballs from its throat or upper gastrointestinaltract. Chronic vomiting in cats may indicate underlying liver or kidney dysfunction and should be investigated by a veterinarian. Dogsalso vomit often (frequently after eating grass) and are also known for eating their own vomit, a fact even cited in the Bible: KJVProverbs26:11 "As a dog returneth to his vomit, so a fool returneth to his folly."

• Owlswill expel the undigestible bones and fur of their meals after partial digestion of the nutritious parts rather than passing them through the digestive tract.

• Some adult birdsregurgitate food to feed their young, triggered by a featheror a beakof 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 predatorcomes near a fulmaron its nest, the bird vomits oil up to 3 feetat the enemy.
• When in danger, the sea cucumbermay eject its entire digestive tract. The animal is able to re-grow another one.
• Some large mammals, including horses, rarely vomit. Many rodents lack the ability to vomit, which is why mice and rats are easily killed by poisoning.

See also

• emetophobia(fear of vomiting)
• emetophilia(sexual fetish)
• regurgitation

External links

• Emetophobia FAQ
• Cyclical Vomiting Syndromeda:Opkast

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It uses material from the http://en.wikipedia.org/wiki/Vomiting Wikipedia article Vomiting.