The Digestive System

May 08, 2023

Digestion

 Digestion is the process of breaking down large, insoluble molecules in food into smaller, soluble molecules that can be absorbed into the bloodstream. These small soluble molecules are used by cells for the release of energy, or to build other molecules.

The digestive system is an example of an organ system in which several organs work together to digest and absorb food.

Tissues & organs of the human digestive system

  • The organs of the digestive system work together to digest and absorb food

Structure

Function

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

 

The digestive system is a series of organs working together to break down and absorb food

The importance of bacteria in digestion

  • The large intestine is home to hundreds of species of bacteria

  • These bacteria form a microbial ecosystem that play an essential role in human digestion of food by, e.g.:

    • breaking down substances we can’t digest

    • supplying essential nutrients

    • providing competition with any harmful bacteria to restrict their growth

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