1. Body Function – Digestion –
Year 10 Human Biology 2015

2. Definitions Mechanical Digestion Chemical Digestion
Physically breaking up large particles into small particles
Chemical Digestion
Chemically breaking up larger molecules into smaller molecules

3. Digestive Process
Six basic activities are carried out by the digestive organs
Ingestion of food
Mechanical digestion of food
Chemical digestion of food
Movement of food along alimentary canal
Absorption of food into blood and lymph
Elimination of food that is not absorbed

4. What is happening at each stage shown in this diagram?

5. Mechanical Digestion - Mouth
Food enters the mouth
Teeth break down the food into smaller pieces
Four different types of teeth perform different functions of mechanical digestion
4 incisors
2 canines
4 premolars
6 molars

6. Mechanical Digestion - Stomach
Waves of muscular contraction move along the muscular stomach wall
Stomach has three layers of muscle allowing is to moved food around like a food processor
Food is churned and mixed with gastric juices
Food is converted into a thick, soup-like substance called chyme

7. Stomach and Liver Relationships

8. Chemical Digestion - Enzymes
Enzymes speed up the chemical reaction
Enzymes are proteins
Enzymes decrease the amount of energy required to start a reaction
Enzymes allow the reactions to continue at a rates that suits the body’s requirement
Enzymes are specific

9. Chemical Digestion - Mouth
Salivary glands secrete saliva into the mouth
Saliva contains mucous and salivary amylase
Salivary amylase is an enzyme that breaks down starch molecules into smaller units
Saliva has many functions

10. Mouth and Oesophagus

11. Chemical Digestion - Stomach
Stomach contains mucosa that resists gastric juices
Gastric glands secrete gastric juices containing hydrochloric acid, mucous and digestive enzymes
Proteins and fats begin to be broken down in the stomach with the help of these gastric juices

12. Chemical Digestion – Small Intestines
Small intestines contain three important fluids – pancreatic juice, bile and intestinal juice
Pancreatic juice is secreted from the pancreas and contains enzymes
Enzymes in pancreatic juice are
Pancreatic amylase
Trypsin (pancreatic protease)
Ribonuclease and deoxyribonuclease
Pancreatic lipases

13. Chemical Digestion – Small Intestines
Pancreatic amylase breaks starch into disaccharides, namely maltose
Trypsin breaks the bond between amino acids in proteins into peptide chains
Ribonuclease and deoxyribonuclease digest RNA and DNA
Pancreatic lipases break down fats into fatty acids and glycerol

14. Defecation Defecation is the removal of waste products
The product that is defecated by the body is called faeces
Faeces consist of
Food waste eg. Fibre, undigested food
Bile pigments
Some excess water

15. Faeces
Faeces-shaped Ice-Cream in a toilet “cone”

16. Toilet Dining!

17. Movement of Materials
Food passes from the mouth to the stomach through the oesophagus in 5-6 seconds
Food remains in the stomach for 2-8 hours but most has left within 4 hours
High carbohydrate foods leave after a few hours
High protein foods take a little longer
High fat foods take the longest time to leave the stomach

18. Movement of Materials
Food passes from the stomach to the small intestines
Movement through the small intestines is fairly slow
It may take up to 5-6 hours to move food through the small intestines
Nutrients are absorbed during this process

19. Small intestines

20. Movement of Materials Food then passes to the large intestines
Movement is very slow through this organ
Water is absorbed during the slow movement
Food may be in the large intestines for hours
Food basically “rots” in the large intestines!

21. From Eating to Defecation
From the time food enters the mouth until such time as it is excreted as waste, it is in our body for:
UP TO 36 HOURS
Therefore you may be defecating (mainly fatty) food that you ate nearly one and a half days ago!
Carbohydrates take about hours
Proteins take about hours

22. Energy Requirements The body needs energy for:
Growth and repair of tissue
Maintaining body temperature
Maintaining normal body functions
Contraction of muscles in physical activity

23. Work to be completed Label the diagram on Digestion
Complete the Unit Review Questions.