Defensive vomiting refers to the use of emesis to defend against ingested pathogens or, in animals, against predators.
Vomiting serves an evolutionary purpose for humans by preventing the ingestion of something harmful, and by expelling noxious substances once ingested.
Vomiting excessive amounts of alcohol is an attempt by the body to prevent alcohol poisoning and death. Vomiting may also be caused by other drugs, such as opiates, or from toxins found in some foods and plants. Food allergies, such as lactose intolerance, can cause vomiting.
Even morning sickness, nausea and vomiting common to most pregnant women but no other mammals, has a defensive purpose. Morning sickness discourages pregnant women from eating meat and strong-tasting vegetables, which may contain toxins and microorganisms. If ingested, the fetus might be harmed. After around the 18th week, the fetus becomes less vulnerable.
The European roller, a much smaller bird found in parts of Africa, Europe, Asia, and the Middle East, uses vomit in a different way. A baby European roller will vomit a foul-smelling orange liquid onto itself to turn away a predator. The smell also warns the parents to return to the nest.
- Area postrema the part of the brain that controls vomiting
- Chemoreceptor trigger zone the part of the area postrema that relays signals through the blood-brain barrier
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