The digestive tract, alimentary canal or gut is a hollow tube stretching from the mouth to the anus. It is the organ system concerned with the treatment of foods.
At the mouth the large food molecules are taken into the gut - this is called ingestion. They must then be broken down into smaller ones by digestive enzymes - digestion, before they can be taken from the gut into the blood stream - absorption. The cells of the body can then use these small molecules - assimilation. The indigestible waste products are eliminated from the body by the act of egestion (see diagram 11.1).
Diagram 11.1 - From ingestion to egestion
The 4 major functions of the gut are:
- 1. Transporting the food;
- 2. Processing the food physically by breaking it up (chewing), mixing, adding fluid etc.
- 3. Processing the food chemically by adding digestive enzymes to split large food molecules into smaller ones.
- 4. Absorbing these small molecules into the blood stream so the body can use them.
The regions of a typical mammals gut (for example a cat or dog) are shown in diagram 11.2.
Diagram 11.2 - A typical mammalian gut
The food that enters the mouth passes to the oesophagus, then to the stomach, small intestine, cecum, large intestine, rectum and finally undigested material exits at the anus. The liver and pancreas produce secretions that aid digestion and the gall bladder stores bile. Herbivores have an appendix which they use for the digestion of cellulose. Carnivores have an appendix but is not of any function anymore due to the fact that their diet is not based on cellulose anymore.