The Digestive System
- Food contains a lot of large, insoluble molecules that need to be broken down into smaller soluble molecules. This is so they can be absorbed and used by the body.
- Digestion is the process of breaking down food which takes place in the organ system called the digestive system.
- The digestive system is made up of the alimentary canal and other organs providing chemicals for digestion.
- Mouth: food is ingested here. Mechanical digestion occurs where the teeth break up the food into smaller pieces to increase SA. This is so digestive enzymes have more area to work on. The tongue forms the chewed food into a bolus, which gets lubricated with saliva, making it easier to swallow.
- Oesophagus: a muscular tube between the mouth and the stomach. The muscles contract in waves to squeeze the food down; this is called peristalsis.
- Stomach: muscular bag that produces acid and enzymes (mostly protease). It churns up food with these juices by peristalsis to make a thick paste.
- Small intestine: this is where most of the large insoluble food molecules are broken down into smaller soluble ones. It contains many digestive enzymes made by the pancreas and also makes its own enzyme. The molecules of food are absorbed by villi which contain capillaries. Food is moved along by peristalsis.
- Pancreas: produces digestive enzymes and releases than into the duodenum (first part of small intestine).
- Large intestine: undigested food passes into this wide, thin walled tube. Water diffuse back into the blood leaving faeces behind.
- Anus: egestion occurs here (undigested food passed out of the body.
- Liver: digested food is absorbed and dissolves in blood plasma. Once in the blood it is taken to the liver via the hepatic portal vein to be processed. Some molecules are broken down furthers and others built up again. The liver also makes bile which helps digestion of fats and neutralisation of stomach acid.
- Gall bladder: stores bile and releases when needed.