1 of 27 Learning Outcomes To explain what digestion is To label all the major organs of the digestive system

2 of 27 The body carries out digestion of food to convert large insoluble food molecules into smaller soluble ones. Carbohydrate Protein Lipid Small food molecules can pass through the walls of the small intestine and then dissolve into the blood stream. Large food molecules cannot do this. What is Digestion ?

3 of 27 Digestive System Salivary Glands Tongu e Teeth Oesophagus Liver Gall Bladder Pancreas Small Intestine Large Intestine Rectum Stomach Anus

4 of 27  Ingestion – into the mouth  Digestion – large to small molecules  Absorption – taken into the blood stream  Assimilation – food is used for jobs  Egestion – faeces out of the body Key words to learn

5 of 27 In the Mouth  Digestion begins in the mouth where food is broken down by the teeth. This is called physical breakdown.  The small parts of food are mixed with saliva and swallowed.

6 of 27 In the Mouth  Saliva contains enzymes that start to chemically breakdown some of the starch and fats in the food.  Enzymes are biological catalysts that speed up chemical reactions.

7 of 27 Enzymes in Action

8 of 27 Amylase and Starch  Amylase breaks the long starch chains into glucose molecules.  How long can you keep a piece of bread in your mouth?

9 of 27 Enzymes are specific  This means that they will only work in certain conditions.  The mouth is slightly alkaline so amylase works best at pH 7-8

10 of 27 EnzymeFunctionOptimum Condition Amylase & Salivary Amylase Break down carbohydrates into glucose Neutral pH ~ 7 Protease (Pepsin) Breaks down protein into amino acids Acidic pH < 7 LipaseBreaks down lipids (fats and oils) into fatty acids and glycerols Weak Basic pH ~ 8

11 of 27 The Journey So Far...

12 of 27 Down to the Stomach  Food then passes the epiglottis, a flap of skin and cartilage that prevents food from entering the trachea (air tube).

13 of 27 Down to the Stomach  The food is moved down the oesophagus with the help of wave like contractions, a process called peristalsis.

14 of 27 In the Stomach  The stomach is a hollow muscular sac with a variety of functions. a) It stores and churns food before moving to the duodenum b) Produces hydrochloric acid (pH 2) and the enzyme pepsin for chemical breakdown of proteins Mucus prevents the acid digesting the wall of the stomach

15 of 27 Mmmmmm… Bile!  Bile – a greeny-yellow substance made by the liver but stored in the gall bladder which emulsifies fats to allow absorption. It also neutralizes the chyme. The bile is released just after food leaves the stomach in the duodenum

16 of 27 As the food goes through the duodenum, it is mixed with: 1. Bile - produced by the liver Bile assists lipase breaking down lipid molecules and also neutralises the acid from the stomach 2. Pancreatic juice - produced by the pancreas Pancreatic juice contains digestive enzymes like lipase (breaks down lipids) and amylase (breaks down carbohydrates)

17 of Name of liquid in stomach? 2. pH of the stomach 3. Name of enzyme in the stomach 4. What food group is digested in the stomach? 5. What protects the stomach from the acid? 6. Name of green liquid made by liver? 7. What is the job of the liquid? Quick recap

18 of 27 Small Intestine  The nutrients diffuse into the blood stream though the wall of the small intestine.

19 of 27 Villi The walls of the small intestine are not smooth. They are covered in villi which increases the surface area

20 of 27 You must be able to describe how the small intestine is adapted for maximum absorption of nutrients!!!

21 of 27  Large surface area  Large blood supply  Thin surface to move across  Blood has low concentration of nutrient which increases the rate of diffusion How it is maximised….

22 of 27 Large Intestine  After the long trip through the small intestine, the remains enter the large intestine.  Here remains are fermented by the action of gut bacteria, excess water is absorbed and faeces is stored until released.

23 of 27 Label the Diagram

24 of 27 Digestion Summary

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27 of 27 Anagrams

28 of 27 Digestion Quiz