Vomiting

Vomiting (emesis or regurgitation) is the expulsion through the mouth of the contents of one's stomach. It is a mechanism for expelling ingested illness causing food, poisons or (in birds) nutrition for the young. The act may be triggered by stimuli which might indicate the possibility of poisoning, such as motion sickness, or sight of decayed food, or other people vomiting. The act may also be triggered intentionally by touching the back of the throat with a finger, feather or beak.

The feeling that one is about to vomit is called nausea.

Examination of the micro-fungal content of vomit can be a means of indentifying illness. Also known as vomitus, vomit contains a high concentration of hydronium and is thus strongly acidic.

The domestic cat is well known for its tendency to vomit, particularly when attempting to dislodge hairballs from its throat or upper gastrointestinal tract.

Some adult birds regurgitate food to feed 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.

In the case of nausea, it can be useful to have a bucket nearby to vomit in if one can not reach a toilet in time. On airplanes (and sometimes on buses and ferries) special bags are supplied for this purpose. Alternatively a special disposable bag is used containing absorbent material that solidifies the vomit in 5 to 10 seconds, making it convenient and safe to keep (leakproof, puncture resistant, odorless) until there is an opportunity to dispose of it (conveniently like regular garbage). It is also used for urination in special circumstances.

Slang terms and synonyms for vomiting: Throw up (phrasal verb), puke, barf, heave, hurl, blow chunks, spew, yack, ralph, retch, chuck, chuck up, upchuck, sick up, spit up, bring up, toss cookies, lose your cookies, lose/blow your lunch, boke, chunder, cack, cascade, disgorge, urp, vurp, hug/worship/pray to the porcelain god/goddess, pray to Dionysus, hug the throne, drive/ride the porcelain bus, technicolor yawn, liquid laugh, laugh at the ground, holler New York, call Earl, paint the walls, talk the Ralph on the big white telephone

Physiological Basis

Vomitting is co-ordinated in the vomitting cenre in the medulla. Receptors on the floor of the fourth ventricle of the brain represent a chemoreceptor trigger zone, stimulation of which leads to vomitting. The chemoreceptor zone lies outside the blood-brain barrier, and can therefore be stimulated by blood born drugs which can stimulate vomitting, or inhibit it. Vomiting entails:

Increased salivation to protect the enamel of teeth from stomach acids.
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.
If the upper esophageal sphincter remains contracted, the person is said to retch, and the contents drain back into the stomach. After a few retches, the upper esophageal sphincter may relax and the vomitus are expelled.

Bile can enter the vomit during subsequent heaves due to duodenal contraction if the vomitting is severe.

The potential physiological complications associated with vomitting are mainly metabolic alkalosis and hypokalemia.