1. Digestion

2. Learning Objectives
Identify and locate the sources of the major digestive enzymes
Summarise the breakdown of carbohydrates, proteins and lipids by enzymes
Explain the necessary conditions for enzymes to work in the human alimentary canal

3. Insoluble to soluble

4. Four Steps of Digestion
1. Ingestion- food entering digestive system
2. Digestion- Break down of food from insoluble lumps to soluble molecules (smallest units)
Mechanical- physical break down of food
Chemical- break down of food catalysed by enzymes
3. Absorption- movement of digested food from the alimentary canal into the blood stream
4. Egestion- removal of undigested food and waste products.

5. Enzymes http://www.biotopics.co.uk/other/anenz.html

7. The Mouth Mouth: begins digestion Teeth (mechanical digestion)
Tongue (mechanical digestion)
Saliva (chemical digestion)
Source: three pairs of salivary glands
Composition: mucous, enzyme, water (carbohydrase) salivary amylase

8. Mouth: begins digestion Teeth (mechanical digestion)
Tongue (mechanical digestion)
Saliva (chemical digestion)
Source: three pairs of salivary glands
Composition: mucous, enzyme (carbohydrase) salivary amylase

9. Carbohydrate Digestion
Takes place in the: mouth, duodenum and jejunum
Chemically digested by the enzymes:
salivary amylase,
amylase,
moltase,
sucrase
lactase.
Source of enzyme
Salivary glands – salivary amylase
Pancreas – amylase
Jejunum wall – moltase, sucrase and lactase

10. Types of Carbohydrate
Starch a very large molecule digested to maltose and then glucose
Lactose a sugar milk digested to galactose and glucose
Sucrose a table sugar digested to fructose and glucose

11. Create a table for Carbohydrases
Digestive enzyme
Source of enzyme
Place of work
Role

12. Do we eat glycogen?
If so where from?

13. Protein digestion Takes place in the stomach, duodenum, and jejunum.
Chemically digested by the enzymes
pepsin,
trypsin
chymotrypsin
carboxypeptidase
peptidase
Gastric glands secretes
pepsinogen
( converted to pepsin by hydrochloric acid)
Pancreas secretes
trypsin
chymotrypsin
carboxypeptidase
Jejunum wall secretes peptidase

14. Endopeptidases Exopeptidases
Break bonds between molecules within the peptide chain. This increases the number of end amino acids
e.g. trypsin and chymotripsin
Exopeptidases
Break bonds between end amino acids in the chain. This frees individual amino acids
e.g. carboxypeptidase and peptidase

15. Protein
Protein is a large molecule made of many sub units called amino acids
Many amino acids joined together make a polypeptide
Several amino acids joined together make a peptide

16. Create a table for peptidases
Digestive enzyme
Source of enzyme
Place of work
Role

17. Fat digestion Takes place in the mouth stomach but mainly duodenum
Chemical digestion by lipase
Bile
Pancreas secrets lipase
Liver makes bile which is stored in the gall bladder and released into the duodenum

18. Fat
Fat forms globules and must be reduced in size to make digestion faster
Bile disperses the large globules into very small ones by emulsification
Lipase is able to work on very small droplets turning them to fatty acids and glycerol

19. Structure of the Stomach Wall

20. Stomach Function Mechanical and chemical digestion
Functions: food storage, digestion, regulation of delivery
Gastric juice: specific cells secrete
Parietal cells- Hydrochloric acid: produces a pH of about 1.0, kills bacteria.
Chief cells- Pepsinogen is converted to active enzyme pepsin by the acid to begin protein digestion
Goblet cells- Mucus: protects stomach lining from acid

21. Gastric pits Goblet cell secret mucus
Oxyntic cells secret hydrochloric acid
Chief cells secret pepsinogen a precursor of pepsin

22. Stomach Contraction mechanical digestion
Stomach contractions: blend food and propel forward
Direction: from cardiac sphincter to pyloric sphincter
Chyme: result of mixing, affects hormone secretions regulating peristalsis and emptying of stomach

23. Gastric ulcer
Helicobacter pylori is one of the most common causes of peptic ulcer. Ulcers can also be caused or worsened by drugs such as aspirin and ibuprofen

24. Pancreas and gall bladder
Pancrease secretes:
the enzymes trypsin, lipase and amylase
Bicarbonate ions to increase the pH in the duodenum
Gall Bladder releases:
Bile to emulsify fat
Bicarbonate ions to increase the pH of the duodenum
Why does the pH need changing?

25. Duodenum This is where:
The acidic chyme from the stomach is converted to an alkaline solution so that pancreatic enzymes can work
polypeptides are digested to peptides by trypsin
Starch is digested to maltose by amylase
Fat is emulsified by bile and digested by lipase to fatty acids and glycerol

27. Jejunum Functions Secrets the enzymes: Structure
Peptidase to digest peptides to amino acids
Maltase to digest maltose to glucose
Sucrase to digest sucrose to glucose and fructose
Lactase to digest lactose to glucose and galactose
Structure
Mucosa adaptations: villi containing blood and lymphatic capillaries

29. Optimum temperature
What is the optimum temperature for enzymes in the digestive system?
40 OC
Explain why it is 40 OC and not 37 OC

30. Ileum
Main Function:
To absorb the soluble molecules, vitamins, minerals and water (8.5 litres) from the lumen of the ileum into the blood

31. Colon
Absorption of:
Water (0.4 litres)
Vitamins
Salts
Soluble fibre is digested by bacteria which results in gas e.g. nitrogen, carbon dioxide, methane, hydrogen sulphide and hydrogen

32. Colon content Stools containing fibre are larger than those without
Large stools will distend the gut
Distension of gut stimulates the peristalsis
Peristalsis is about twice an hour in the colon

34. Try the activity Enzymes linked to food types
Food type – enzyme – product – place

35. Have a go at the massive gap fill

36. Learning Objectives List the 4 main functions of the digestive system
Define an enzyme
Outline the difference between chemical and mechanical digestion
Describe the role of peristalsis in the movement of the contents of the gastrointestinal tract
Describe the role of the stomach in mechanical and chemical digestion including the composition of gastric juice
Describe the role of bile and pancreatic juice in digestion in the duodenum
Describe the role of the jejunum
Described the role of the colon