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):
Churning (Stomach):
Movement of Food
Peristalsis:
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