Mechanical Digestion

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•  The contraction of circular and longitudinal muscle of the small intestine mixes food with enzymes and moves it

    along the gut

Food can be digested by a combination of two methods – mechanical digestion and chemical digestion

  • In mechanical digestion, food is physically broken down into smaller fragments via the acts of chewing (mouth), churning (stomach) and segmentation (small intestine)

Mechanical Digestion

Chewing (Mouth)

  • Food is initially broken down in the mouth by the grinding action of teeth (chewing or mastication)
  • The tongue pushes the food towards the back of the throat, where it travels down the esophagus as a bolus
  • The epiglottis prevents the bolus from entering the trachea, while the uvula prevents the bolus from entering the nasal cavity

Churning (Stomach)

  • The stomach lining contains muscles which physically squeeze and mix the food with strong digestive juices ('churning’)
  • Food is digested within the stomach for several hours and is turned into a creamy paste called chyme
  • Eventually the chyme enters the small intestine (duodenum) where absorption will occur

Movement of Food


  • Peristalsis is the principal mechanism of movement in the oesophagus, although it also occurs in both the stomach and gut
  • Continuous segments of longitudinal smooth muscle rhythmically contract and relax
  • Food is moved unidirectionally along the alimentary canal in a caudal direction (mouth to anus)


  • Segmentation involves the contraction and relaxation of non-adjacent segments of circular smooth muscle in the intestines
  • Segmentation contractions move chyme in both directions, allowing for a greater mixing of food with digestive juices
  • While segmentation helps to physically digest food particles, its bidirectional propulsion of chyme can slow overall movement