How Vomiting Occurs?

Nausea is the subjective feeling of a need to vomit and vomiting or emesis is the expulsion of gastrointestinal contents through mouth, which is due to contractions of gut and thoraco-abdominal wall musculature. Vomiting should be differentiated from regurgitation, which is effortless passage of gastric contents into the mouth.

Vomiting occurs due to stimulation of ‘vomiting center’ which is situated in the medulla oblongata in the brain. Multiple pathways can elicit vomiting. Generally CTZ (chemoreceptor trigger zone) and NTS (nucleus tractus solitarious) are major relay centers of vomiting. Impulses which arise from GIT (gastrointestinal tract), throat or other viscera are relayed through CTZ and/or NTS to “vomiting center” and cause vomiting. CTZ is also accessible by many blood borne drugs, hormones, toxins and mediators which can cause vomiting, because CTZ is not protected by BBB (blood brain barrier).

Many toxic drugs, radiation or other gastrointestinal irritants cause release of 5-HT (5-hydroxy tryptamine) and acts on 5-HT3 receptors present in the vagus nerve endings in stomach, which in turn send impulse to CTZ and NTS and cause vomiting. Sufficient quantity of 5-HT can be released from platelets and from other sources and cause vomiting. Other than 5-HT, there are also other messengers and peptides which can act as trigger for vomiting.

CTZ and NTS also has other receptors like dopamine receptors, opioid receptors, histamine receptors, cholinergic receptors, stimulation of any of these can cause vomiting.

The vestibular apparatus present in the inner ear can also generate impulses when body equilibrium is disturbed, body is rotated or due to drugs which are toxic to inner ear. These impulses reach vomiting center directly and cause vomiting and affect patients’ health state adversely. Many unpleasant sensory stimuli such as obnoxious smell, ghastly sight, severe pain and fear, recall of previous unpleasant event, anticipation of some stimulus (e.g. repeat dose of some anti cancer drugs) etc. can cause vomiting through higher centers.

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1 Comment

  • CNA Training November 11, 2010 12.03 pm

    I was not aware of how vomiting occurs. But this article helped me a lot. Very nice article. Thanks.

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