Digestive system
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
esophagus
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 organ 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:
o ingestion: food and drink are taken into the body through the mouth
o mechanical digestion: food is broken down into smaller pieces without chemical
change to the food molecules
o chemical digestion: large, insoluble molecules are broken down into small,
soluble molecules
o absorption: small food molecules and ions move through the wall of the intestine
into the blood
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
egestion: food that has not been digested or absorbed passes out of the body as faeces
Digestive system functions table
Structure Function
Mouth Food is ingested here and the teeth break it down into smaller pieces during mechanical
digestion
Saliva is secreted into the mouth
Salivary glands The enzyme amylase in saliva begins to digest starch into maltose
Saliva lubricates the food for easy swallowing
This tube connects the mouth to the stomach
Oesophagus
Contractions of the walls of the oesophagus force the food downwards; this is peristalsis
Churning of the muscular stomach walls continues the process of mechanical digestion
Pepsin enzymes begin protein digestion
Stomach
Hydrochloric acid provides a suitable pH for the enzymes and also destroys any pathogens
in food
Bile is produced here
Liver
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
Amylase, protease and lipase enzymes are produced here before being released into the
Pancreas
duodenum
Food enters the small intestine from the stomach here
Small intestine The acidic stomach contents are neutralised by bile and become slightly alkaline
Enzymes complete chemical digestion here
Food and water are absorbed into the blood via villi in the lining of the ileum
Remaining water is absorbed from food into the blood, and the solid waste left behind in
Large intestine: colon
the colon forms faeces
Large intestine:
Faeces are stored here prior to egestion
rectum
Large intestine: anus Faeces leave the body via the anus; this is egestion
