1. Ch 21
Human Digestive
System

2. Need to know
The definition of Autotroph, heterotroph, herbivore, carnivore, omnivore and examples of each
Understand the need for digestion and a digestive system
Know the definition of ingestion, digestion, absorption, egestion.

3. The way an organism obtains and uses its food
Nutrition
The way an organism obtains and uses its food

4. Autotrophic Heterotrophic
A type of nutrition where organism make its own food
A type of nutrition where organism cannot make its own food
Heterotrophic

5. Herbivores Carnivores Animals that feed only on plants e.g. rabbit
Animals that feed on other animals e.g. fox

6. Omnivores
Animals that feed on plants and animals e.g. Badger

7. Digestion definition Need for Digestion
The physical and chemical breakdown of food into soluble particles small enough to pass into body cells
Need for Digestion
To breakdown large food particles until they are small enough to pass into body cells

8. Stages in Human Nutrition
Ingestion
Food is taken into the mouth
Food is broken down into smaller soluble pieces
Digestion
The movement of digested from the alimentary canal into the blood stream
Absorption
Egestion
Removal of undigested /unabsorbed food as faeces

9. Digestion 1.

10. Learning check Define Autotroph, heterotroph, Herbivore, Carnivore,
Omnivore & Give an examples of each
Explain (a) the need for digestion (b) the need for a digestive system
Define ingestion,
digestion,
absorption,
egestion

11. Need to know
The functions of the main parts of the alimentary canal and the associated glands
Function of teeth .
The human dental formula
Role of mechanical digestion and peristalsis
Details of chemical digestion by one amylase, one protease and one lipase .
Role of bile salts
Symbiotic bacteria functions in the large intestine
Benefits of fibre

12. The Digestive System

13. Diagram label

14. Mechanical breakdown of food
Teeth
Contractions in stomach wall
Peristalsis
Rhythmic muscular contraction and relaxation in the wall of the alimentary canal causing the food to move along the canal

15. The Mouth Contains a muscular tongue and a set of teeth.
Secretes a juice called saliva from the salivary glands.
Saliva contains water,
salts, and the enzyme
Salivary amylase.
3,000 taste buds

16. Baby Teeth! First set of teeth in humans are milk teeth
– no molars present

17. The Mouth – Physical Digestion
Physical digestion by chewing action of teeth results in smaller particles of food, easier to swallow + greater surface area for digestion

18. Human Teeth Incisors Cutting Canines Tearing Pre molars
Crushing and grinding

19. 4 types of teeth Incisors – sharp edges, cuts, slices and bites
Canines – Long and pointed, grip, stab and tear food
Premolars – Have cusps they crush and chew food
Molars- Large teeth at the back also crush and chew food

20. Human dental Formula Incisors Canines Pre molars Molars c pm m i
The number of each type of tooth in the upper jaw one side of the mouth
Incisors
Canines
Pre molars
Molars pm 2 m 3 i 2 c 1

22. The Mouth – Chemical Digestion
Chemical digestion takes place due to the presence of the enzyme salivary amylase
This is found in saliva which is secreted by 3 pairs of salivary glands

23. Saliva Consists of water, salt and Salivary amylase
The water lubricates the food.
The salt provides a slightly alkaline medium (pH 8) which Salivary Amylase works best at
Salivary Amylase breaks down starch into maltose

24. Learning check 1 Name four types of teeth
Name the parts of the digestive system
Learning check 1
Name four types of teeth
Write down the human dental formula
State the function of each of the four types of teeth

25. Learning check 2 Mechanical breakdown of food involves what 3 things?
Explain how the mouth is involved in Physical Digestion
Name the 4 types of teeth & give their functions.
What is the Human dental Formula?
Explain how the mouth is involved in Chemical Digestion.
Define peristalsis.
What is saliva?

26. Oesophagus
A hollow muscular tube, 25 cm long that connects the mouth to the anus.
The walls of the Oesophagus secrete mucus and the food is moved by Peristalsis

27. Oesophagus (Food Pipe)

28. Stomach J shaped muscular bag Stores food for about 4 hours
Chemical & Physical digestion takes place in the stomach
7 seconds for food to reach stomach from d mouth!

29. Sphincter Muscle Location
Cardiac Sphincter Muscle
Circular muscle which contracts to close entry from oesophagus to stomach
Pyloric Sphincter Muscle
Circular muscle which contracts to close the entry to duodenum from the stomach.
(Open when relaxed )

30. Digestion in the Stomach
Mechanical Digestion Peristalsis physically mixes up the food with gastric juices
Chemical Digestion using
Gastric Juice containing:
Mucus
HCL
Pepsin

31. Lining of the Stomach
The lining of the stomach is very muscular and highly folded
Millions of gastric glands line the stomach
producing
gastric juice

33. Functions of gastric juice
Mucus - Lines and protects the stomach wall from HCL & pepsin
HCL – a. Kills bacteria
b. Activates pepsin, by lowering the pH
Pepsin - Pepsin is an enzyme produced by the cells lining the stomach. Pepsin breaks downs protein into peptides

34. Hydrochloric acid This gives stomach a pH of 1 to 2! Very acidic
This acidity kills many bacteria, loosens fibrous and cellular foods,
activates pepsin and
denatures amylase from saliva
too much acid in the stomach leads to heartburn – can be neutralised with alkalis such as alka seltzers or Rennies

35. Ulcers
If gastric juice does manage to digest the stomach wall ulcers can result
If ulcer becomes perforated bacteria could get into body and cause death

36. Learning check 3 What is the Oesophagus?
What is involved in Mechanical Digestion in the stomach?
What is involved in Chemical Digestion in the stomach?
What is the lining of the stomach made up off?
Why are gastric juices made up off?
Why is the function of HCL in the stomach?

37. Small Intestine Muscular tube 5-6m long Functions: Digestion
Absorption
Has three parts
duodenum
jejunum
3. ileum

38. Duodenum
25cm muscular tube
Most digestion takes place in the duodenum

40. Food / acid chyme arrives in from the stomach
This stimulates the production of pancreatic juice from the pancreas, bile & gall bladder
Cells that line the duodenum produce:
Digestive juices &
Enzymes
These all mix together.

41. Pancreas Lies beneath the stomach
Produces pancreatic juices which contain
water
sodium bicarbonate salt to neutralise chyme from the stomach and
enzymes
The pancreatic duct leads from the pancreas to the duodenum

42. Pancreatic Enzymes Contain enzymes which break down food:
Pancreatic amylase which converts starch to maltose
Pancreatic lipase which converts lipids to fatty acids & glycerol
Pancreatic protease / trypsin which converts proteins to peptides

43. Bile Made in the Liver & stored in the gall bladder
Passes into the duodenum via the bile duct
It contains
Sodium bicarbonate – neutralises the acid chyme from the stomach & provides an alkaline environment
Organic salts which emulsifies fats.

44. The Ileum - Absorption In the duodenum: Lipids were broken down
into fatty acids
Carbohydrates into monosaccharides
Proteins into amino acids.
These digested food then pass through the ileum wall and are absorbed into the blood and lymph systems.

46. The lining of the Ileum - Villi
Villi are tiny infoldings in the lining of the ileum, which consist of smaller infoldings – microvilli
Function: Increase the surface area for absorption of digested food.

47. Villi details

48. The products of fat breakdown - Fatty acids and Glycerol are reconverted to tiny fat droplets
They pass into the lymph vessels / Lacteals, found inside each villi, which are part of the lymphatic system.
Eventually the return to the bloodstream
And then to the Liver.

49. Fat digestion & absorption

50. The products of
Carbohydrates (monosaccharides) and
Proteins (amino acids) breakdown
Mineral
Vitamins
Pass via the villi from the small intestine to the the bloodstream
They are then carried via the Hepatic portal vein to the Liver

51. Digestion 5

52. Learning check 4 The Small Intestine is made up 3 parts?
State two ways in which the small intestine is adapted to absorb digested food
Cells that line the duodenum produce ?
How are the products of fat digestion transported away from the small intestine

54. The Liver
Digested food material except fats are brought to the Liver via the Hepatic portal vein.
The Hepatic artery brings oxygenated blood from the heart.
The Hepatic vein brings blood from the Liver to the heart.

55. Functions of the Liver
Detoxifies the body – breaks down poisons such as alcohol and drugs
Breaks down excess amino acids to form urea
Converts glucose to glycogen for storage
Converts excess carbohydrate to fat
Produces Bile
Stores vitamins (e.g. vit D)
Stores minerals (e.g. Iron)
Produces heat to warm
the blood and the body

56. Large Intestine
1m Long
Colon
Caecum
Appendix
Rectum
Anus

57. Functions of the Large Intestine Colon
Reabsorb water & mineral salts into the blood
Symbiotic Bacteria live in the colon
produce Vitamins B & K
Prevent growth of pathogenic bacteria

58. Digestion 4

59. Learning check 4
State two ways in which the small intestine is adapted to absorb digested food
What are the main functions of the large intestine
How are the products of fat digestion transported away from the small intestine
Give the function of the liver in digestion

60. Fibre
The remaining undigested food eventually passes into the Large Intestine.
Fibre (Roughage) consists of cellulose from plant cell walls which humans cannot digest
Stimulates peristalsis in the colon by providing bulk against which muscles of the gut wall push against.
Helps prevent constipation

61. Caecum Appendix Rectum Function unknown in humans
Stores faeces bacteria, unabsorbed food, cells from the intestine wall, bile pigments and mucus

62. Caecum and Appendix are Vestigial organs in humans - they have lost their function
Sometimes bacteria gather and grow in the appendix, bacterial waste builds up and causes pain if appendix ruptures it can be very serious

63. Learning check 3
State ONE way in which the small intestine is adapted to absorbing digested food
How are the products of fat digestion transported away from the small intestine?
What are the main functions of the large intestine?

64. Need to know Understand the term balanced diet
Learn the main human food groups
Understand how variety and moderation are important in having a balanced diet
Draw a human food pyramid
Relate human diet to age, gender and activity level
Learn the recommended daily servings of each of the main food groups

65. Balanced Diet
Taking the correct amounts of all the essential nutrients in the diet
Carbohydrate
Vitamins
Protein
Minerals
Fat
Fibre
Water

66. A Balanced Diet Seven components Carbohydrate Lipid Protein Minerals
Vitamins
Fibre
Water

67. The amount of food a person requires
depends on age, activity, gender and
Health
Four food groups are:
Cereals breads and potatoes
Fruit and Vegetables
Milk cheese and yoghurt
Meat, fish and poultry

68. Build a Food Pyramid Cereals, Breads, potatoes Fruit Vegetables
Milk, Products
Fruit
Meat Fish Poultry
Oils Fats Alcohol
Vegetables

69. Food Pyramid Very few 2 - 3 3 - 5 Fruit Vegetables
The daily food portions types an average adult should eat
Oils Fats Alcohol
Very few
2 - 3
Milk, Products
Meat Fish Poultry
Fruit
Vegetables
3 - 5
Cereals, Breads, potatoes
6 - 11

70. A Balanced Diet

71. Learning check Define Balanced diet List the five main food groups
Give two general ways to ensure a balanced diet
Draw a human food pyramid
State the recommended daily average number of servings of each food groups

72. Three enzymes involved in digestion
Enzymes are biological catalysts
1 Amylase
2 Pepsin
3 Lipase

73. Salivary amylase
Digest starch
Role
Production site
Salivary glands
Where it acts
Mouth
pH in mouth
Alkaline, pH =8
Digestion product
Maltose

74. Pepsin
Digest protein
Role
Production site
Gastric glands in Stomach wall
Where it acts
Stomach
pH in mouth
Acid, pH =2
Digestion product
Peptides

75. Lipase Digest fat Role Production site Pancreas Where it acts Dudenum
pH in mouth
Alkaline, pH =8
Digestion product
Fatty acids + Glycerol

76. Learning check 4 Explain the benefits of fibre in the diet
Name a protease enzyme
Give the site of action of the protease and state the pH at this location
What is the product of the action of the protease

77. End