Vomiting Vomiting Subsidy Category="Reflexes"Category="Symptoms"Vomiting (or emesis) is the forceful expulsion of the contents of one's Stomach through 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 Gastritis to 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. Antiemetics are 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 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 which 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 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.
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 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 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. 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 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
As the stomach secretes acid, vomit contains a high concentration of hydronium ions and is thus strongly acidic. The potential physiological complications associated with excessive vomiting are mainly metabolic alkalosis (increased blood PH), Hypokalemia (Potassium depletion) and Hypochloremia (Chlorine depletion). The hypokalemia is an indirect result of the Kidney compensating for the loss of acid.

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".

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 and Hepatitis
Sensory system and brain
Causes in the Sensory system:

Movement: Motion sickness (which is caused by overstimulation of the labyrinthine canals of the ear)
Meniere'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 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
Opioids, many Chemotherapy drugs and a host of other drugs may cause nausea and vomiting.
Other

Self-induced

Eating disorders (Anorexia nervosa or 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)

After Surgery (Postoperative nausea and vomiting)
The sight or smell of decayed food, or others' vomit
Extreme pain, Myocardial infarction (heart attack)
Pregnancy (Morning sickness, Hyperemesis gravidarum)
Violent emotions
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 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.

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 to also vomit. This tendency in human populations has been observed at drinking parties, where excessive consumption of alcoholic beverages may result a number of party members vomiting nearly simultaneously, this being triggered by the initial vomiting of a single member of the party.

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 disorder such as Bulimia nervosa) may devise various ways to hide this abnormality.

In language

As with other physiological processes involving body wastes, vomiting has Taboo aspects. This is shown by the large number of colourful euphemisms for vomiting. (see: Toilet humour)

In other animals

Whales vomit regularly (every 7 to 10 days) as a means of the ordinary digestive process, to expel inedible things 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 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 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.
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, rarely vomit. Many rodents lack the ability to vomit, which is why mice and rats are easily killed by poisoning.

External links

Emetophobia FAQ
Cyclical Vomiting Syndrome

Mechanism

Content

Causes

Digestive tract

Sensory system and brain

Other

Related medication

Emetics