Understanding:
• 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
- 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
- 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