Digestive System (Cambridge (CIE) IGCSE Biology)
Revision Note
Written by: Lára Marie McIvor
Reviewed by: Lucy Kirkham
Digestive system: organs
The digestive system is an example of an organ system
Some of the digestive system organs make up the alimentary canal; food passes directly through these organs as it moves through the body:
mouth
oesphagus
stomach
small intestine, including the duodenum and the ileum
large intestine, including the colon, rectum and anus
Some of the organs of the digestive system do not form part of the route travelled by food, but are still involved with digestion; these are the associated organs, or accessory organs, and include the:
salivary glands
pancreas
liver
gall bladder
Digestive system organs diagram
The organs of the human digestive system work together to digest food and absorb nutrients
Digestive system: function
The function of the digestive system is to digest food and absorb nutrients
The digestive system carries out its function in several stages:
ingestion: food and drink are taken into the body through the mouth
mechanical digestion: food is broken down into smaller pieces without chemical change to the food molecules
chemical digestion: large, insoluble molecules are broken down into small, soluble molecules
absorption: small food molecules and ions move through the wall of the intestine into the blood
egestion: food that has not been digested or absorbed passes out of the body as faeces
Once nutrients have been absorbed into the blood by the digestive system they can be assimilated into the body; this occurs when they are taken up by the cells of the body
Digestive system functions table
Structure | Function |
|---|---|
Mouth | Food is ingested here and the teeth break it down into smaller pieces during mechanical digestion |
Salivary glands | Saliva is secreted into the mouth The enzyme amylase in saliva begins to digest starch into maltose Saliva lubricates the food for easy swallowing |
Oesophagus | This tube connects the mouth to the stomach Contractions of the walls of the oesophagus force the food downwards; this is peristalsis |
Stomach | Churning of the muscular stomach walls continues the process of mechanical digestion Protease enzymes begin protein digestion Hydrochloric acid provides a suitable pH for the enzymes and also destroys any pathogens in food |
Liver | Bile is produced here Bile aids the digestion of fats, as well as neutralising stomach acid as it exits the stomach |
Gall bladder | Bile is stored here before being released into the duodenum via the bile duct |
Pancreas | Amylase, protease and lipase enzymes are produced here before being released into the duodenum |
Small intestine: duodenum | Food enters the small intestine from the stomach here The acidic stomach contents are neutralised by bile and become slightly alkaline Enzymes complete chemical digestion here |
Small intestine: ileum | Food and water are absorbed into the blood via villi in the lining of the ileum |
Large intestine: colon | Remaining water is absorbed from food into the blood, and the solid waste left behind in the colon forms faeces |
Large intestine: rectum | Faeces are stored here prior to egestion |
Large intestine: anus | Faeces leave the body via the anus; this is egestion |
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