The digestive system

Digestive phenomena

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Vomiting is the expulsion of part of the contents of the stomach back through the mouth.

It is  a mechanical reflex enabling the body to have a defence against ingesting toxic substances and also against excess food.

Some causes:

  • Food poisoning
  • Digestive tract diseases (ulcers, gastroenteritis)
  • Travel sickness, vertigo
  • Side-effects of certain medication
  • Too much food

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When we vomit, some of the contents of the stomach are expelled by the mouth. This is a defence mechanism in case we swallow toxic substances. Vomiting can be manually triggered, but it is usually a reflex. This reflex first induces a feeling of nausea, or feeling sick, and then the stomach contents are expelled through an anti-peristaltic movement.

As mentioned previously, peristaltic waves are rhythmic contractions that help food move down through the digestive tract, but when we vomit, the contents of the stomach move up in the opposite direction, which is why we refer to an ‘anti-peristaltic’ movement.

When we swallow, the epiglottis turns down to block the glottis, which is the entrance to the larynx. There is a small leaf-shaped flap over the top of the glottis, hence the name epiglottis, from the Greek ‘epi’ meaning ‘upon’.

When we throw up, a reflex closes the glottis to prevent the vomit from going into the trachea and then the lungs.

Vomit typically contains food, along with bile and more rarely blood. Vomiting is not the same as regurgitation, which is a passive action corresponding to the contents of the stomach coming back up towards the back of the throat or the oral cavity.


As with stomach aches, vomiting can be caused by various things. Food poisoning for example, or diseases of the digestive tract, such as a stomach ulcer or gastroenteritis, which is an inflammation of the wall of the digestive tract. Sometimes vomiting is related to balance functions inside the ear, such as motion sickness or vertigo. Side effects of certain medication may also trigger vomiting.

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