1. Alimentary Canal (Digestive system)
Lesson 55
Alimentary Canal (Digestive system)

2. Aims of the Session
This session will allow candidates to have an understanding of the principles of nutrition in relation to digestion.

3. Learning Outcomes
By the end of the lesson the candidate will be able to
Describe the structure and function of the digestive system

4. The Digestive System
The digestive system can be seen as the bodies own food processing factory,
It is a collective name used to describe the alimentary canal,
A variety of digestion processes take place in the canal to prepare food eaten ready for absorption.

5. The Digestive System
Foods cannot always be broken down immediately ready for absorption,
They need to be broken down to there individual compounds throughout the GI track,
i.e. meat, even when cooked is chemically too complex to be absorbed immediately,
Therefore It goes through a series of changes which releases its constituent nutrients, amino acids, mineral salts, fat & vitamins.

6. The Digestive System
Enzymes used for this purpose are secreted from specialised glands both inside and outside via ducts,
After absorption, nutrients are used to synthesise body constituents,
They provide the raw materials for the new cells, hormones, enzymes and energy,
The activities of the digestion system can be grouped under five main headings.

7. The Digestive System Ingestion 2. Propulsion – (peristalsis),
3. Digestion – this consists of,
Chewing (mastication)
Chemical digestion
4. Absorption
5. Elimination

8. Purpose of Digestion
There are a number of key stages in the breakdown and assimilation of nutrients from the foods that are ingested during meals or snacks, they are;
Mechanical breakdown in the mouth,
Chemical breakdown in the stomach and small intestine,
Absorption of nutrients in the small intestine,
Absorption of water in the large intestine,
Excretion of waste products.

9. Student
Task

10. Student Task Mouth Pharynx Oesophagus Stomach Pancreas Liver
Gall Bladder
Small Intestines
Large Intestines
Rectum / Anus

11. The Mouth

12. The Mouth

13. Pharynx & Oesophagus

14. Pharynx & Oesophagus
Tongue & cheek muscles push the bolus into the pharynx, (voluntary)
Muscles within the pharynx contract involuntarily via the Medulla & Pons of the brain stem,
The presence of the bolus in the pharynx stimulates a wave of peristalsis which propels the bolus through the oesophagus into the stomach.

15. The Function of the Digestive System
The digestive system can be seen as the bodies own food processing factory,
It breaks down food, so nutrients can be absorbed, it then excretes any remaining substances from the body

16. The Stomach

17. The Small Intestines

18. The Small Intestines Small intestines leads to the large intestines,
It consists of 3 parts,
Duodenum – 25 cm long, with secretion from the gall bladder and pancreas entering here,
Jejunum – 2 metres,
Ileum – 3 metres.

19. The Small Intestines
In the small intestines digestion of all nutrients is completed via,
Amylase enzyme – breaks carbohydrates down to monosaccharide's,
Trypsin enzymes – break proteins down to amino acids,
Lipase enzymes – break fats down to fatty acids and glycerol.

20. The Large Intestines, Rectum & Anal Canal

21. The Large Intestines, Rectum & Anal Canal
This is about 1.5 metres long and runs to the rectum ,
Its purpose is to absorbs any remaining water, vitamins and minerals,
Bacteria – produce some vitamins and fight infection in intestine,
Rectum is approximately 13cm long and stores faeces ready for defaecation via the anus.