Lesson Topics

2 | Overview of the Digestive System

3 | The Alimentary Canal

4 | The Mouth, Pharynx and Oesophagus

5 | The Stomach

6 | The Small Intestine

7 | The Liver, Gall Bladder and Pancreas

8 | The Large Intestine

9 | Digestion in Other Animals

10 | Summary

Lesson Summary

• The process whereby the body converts food into a form that it can use is called digestion.

• There are five major steps involved in digestion.

• Ingestion – the taking in of food.

• Mechanical digestion – the physical breakdown of food.

• Chemical digestion – the chemical breakdown of food.

• Absorption – the movement of digested food into the bloodstream.

• Defecation – the removal of waste products.

• The digestive system is a group of organs that work together to perform the process of digestion.

• During the process of digestion, food passes through the alimentary canal (gastrointestinal tract) that begins with the mouth and ends with the anus.

• The movement of food through the alimentary canal is achieved by muscular contractions called peristalsis.

• Organs that form part of the alimentary canal are:

• The oral cavity (mouth) – the entry point of food, containing teeth for physical breakdown of food and the tongue for mixing food into a bolus.

• The pharynx – a short tubular section connecting the oral cavity to the oesophagus (as well as the trachea).

• The oesophagus – a muscular tube connecting the pharynx to the stomach.

• The stomach – a large J-shaped sac located in the abdomen that continues the physical breakdown of food and begins the chemical digestion of protein; it secretes gastric juice – a combination of mucus, digestive enzymes and hydrochloric acid.

• The small intestine – a long, convoluted tube consisting of the duodenum – a short section where chemical digestion is completed – and the jejunum and ileum – long, coiled sections containing villi, where absorption of digested food takes place.

• The large intestine – a folded tube consisting of the colon – where water and electrolytes are absorbed, the rectum – where faeces is stored – and the anus – the exit point for faeces.

• Other organs of the digestive system that are not part of the alimentary canal are:

• Salivary glands – glands located around the jaw that secrete saliva to assist chewing and swallowing, as well as the chemical digestion of carbohydrates.

• The liver – a large organ that produces bile, which solubilises fats.

• The gall bladder – a small pouch where bile is stored.

• The pancreas – a leaf-shaped organ that produces enzymes that digest fats, protein and carbohydrates.

• Herbivores rely on internal microorganisms for the digestion of cellulose.

• Herbivores include hindgut fermenters, which digest cellulose in the caecum, and foregut fermenters, which digest cellulose before it enters the ‘true’ stomach.

• Herbivores usually possess large, flattened teeth for grinding up food.

• Carnivores have simpler and shorter digestive systems than herbivores because meat is much easier to digest than plant material.

• Carnivores usually possess long, sharp teeth for tearing and cutting meat.

(Image: Acabashi, Wikimedia Commons)

(Header image: magicmine, Adobe Stock)