The Human Digestive System (AQA GCSE Combined Science: Trilogy: Biology): Revision Note

Mouth

• Food is ingested here and the teeth break it apart during mechanical digestion, increasing its surface area for chemical digestion

Salivary glands

• Saliva is secreted into the mouth

• The enzyme amylase in saliva begins to digest starch into maltose

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; it 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 small intestine

Small intestine

• The acidic stomach contents are neutralised by bile and become slightly alkaline

• Enzymes complete chemical digestion

• Food and water are absorbed into the blood via villi

Large intestine

• Remaining water is absorbed from food into the blood, and the solid waste left behind in the colon forms faeces

Rectum

• Faeces are stored here prior to egestion

Anus

• Faeces leave the body via the anus; this is egestion