11. Human Digestive System - E-Learning

1. Human Digestive System

2. Lesson Objectives
• At the end of this topic, you should be able to:
o explain the importance of the digestive system
o identify the main parts of a digestive system and how they work
together to perform a function
o describe how a digestive system helps in digestion of food and
the part played by enzymes in digestion (Only classes of
enzymes such as amylase, protease and lipase are needed.
Specific names of enzymes not required.)
o infer that the end products of digestion are used for cellular
processes like respiration, growth and tissue repair
o show an awareness of the importance of hygiene habits and
food handling practices in preventing food-borne diseases

3. Hungry?

4. Section 1: Importance of
Digestive System

5. Why We Need To Eat?
• We need food to:
o provide energy for our daily activities like
walking
o grow new cells and tissues
o repair worn-out or damaged tissues
o maintain a healthy body
o produce heat to maintain our body
temperature

6. What is in the Food We Eat?
• Food in our diet contains nutrients that are
essential for our health
• The types of nutrients can be found in the food
label on a food package.
• The food label lists the nutrient content of the
food.

7. Food Labels

8. Main types of nutrients
• The three main types of nutrients:
carbohydrates, proteins and fats.

9. Main types of nutrients
• Carbohydrates
o It is a source of energy that the body uses
first.
o It consists of the elements carbon, hydrogen
and oxygen.
o It is commonly found in food containing
starch and sugars.

10. Main types of nutrients
• Carbohydrates
o Starch can be found in rice, bread, noodles and
potatoes.
o Sugars such as sucrose, glucose and maltose are
found in fruits like bananas and apples
o Cellulose is another type of carbohydrates, which
can be found in plants. This cannot be digested by
the body and it forms part of the dietary fibre
(roughage) that is passed out from the body as
faeces.
• Excessive intake of carbohydrates will be converted
into fats and are stored in the body.

11. Main types of nutrients
• Proteins
o Proteins are very large molecules that are
made up of several small molecules called
amino acids.
o Proteins are needed to:
• form new cells for body growth
• repair of worn-out tissues.
• make more complex proteins such as enzymes that
carry essential functions in the body.
o Proteins can be found in meat, fish and eggs.

12. Main types of nutrients
• Proteins
o It can also supply
energy when the
body has used up all
the carbohydrates and
stored fats.

13. Main types of nutrients
• Fats
o Fats are large insoluble molecules that are
made up of glycerol and fatty acids.
o It is a source of energy that is stored in the
body.
• Fats release twice as much energy as do
carbohydrates.

14. Main types of nutrients
• Fats
o Fats are also stored under our skin to
insulate our body and prevent heat loss.
o Fats are usually solid at room temperature,
melting to liquid at higher temperatures to
form oil.
o Fats can be found in food like butter and
cheese.
Fats are
solids and
oils are
liquids.

15. Definition of Digestion
• The breakdown of large insoluble
food molecules into small soluble
molecules to be absorbed into the
body cells.

16. Why Must Food be Digested?
• Remember the cell membrane?
It is a partially permeable membrane.
• We need digestion because the cell membrane has
small openings (or pores) that allow small
molecules to enter, but not large molecules.
• Nutrients like glucose and amino acids are such
small molecules that can pass through the cell
membranes easily and enter the bloodstream.

17. Nutrients like
starch,
proteins and
fats, are large,
complex
molecules.
They cannot
pass through
the cell
membrane.
Nutrients like glucose
and amino acids, are
small, soluble molecules.
They can pass through
the cell membrane.

18. Checkpoint Time
a) You have just eaten a bowl of chicken
noodles in soup for lunch. State the
nutrients present in your meal.

19. Checkpoint Time
b) Suggest what should be added to the
meal to make it a more balanced diet.
Why ?

20. Section 2: Human Digestive System

21. Types of Digestion
• There are two types of digestion.
• Physical digestion is the breakdown of food into
smaller pieces without any change to the
molecules of the food.
• Chemical digestion is the breakdown of large
food molecules into smaller molecules by the
action of enzymes.

22. Physical Digestion
• Physical digestion occurs in the:
o mouth, where the teeth chew the food into
smaller pieces.
o stomach, where it churns to break down
food into smaller pieces.
To churn means
to shake with
violence or
continued motion

23. Physical Digestion
• Smaller pieces of food have a larger total
surface area for enzymes to act on.

24. Physical Breakdown
PHYSICAL

25. Chemical Digestion
Our body is able to carry out chemical
digestion by producing complex proteins
called enzymes.
Chemical digestion is the breakdown of
large food molecules into smaller
molecules by the action of enzymes.

26. What are Enzymes?
• Enzymes are complex proteins that speed up
the rate of chemical reactions, while remaining
unchanged at the end of chemical reactions.
• Enzymes act like chemical ‘scissors’.
• They break down large molecules into small
molecules to speed up the process of digestion.
• The enzymes involved in digestion are called
digestive enzymes.

27. “Lock and key” hypothesis
• Each type of enzyme is specific. It can
only bind and help to digest one type of
food.
active sites
Enzyme
molecule
Food
molecule
Enzyme-food
complex
Enzyme free
to take part in
next reaction.
Two products
leave the
enzyme.
Product X
Product Y

28. Types of digestive enzymes
• For example, enzymes that break down proteins cannot
break down starch or fats.
Class of
enzyme
Acts on Digested product(s)
Amylase Starch Maltose (a complex sugar)
Maltase Maltose Glucose (simple sugar)
Protease Proteins Amino acids
Lipase Fats Fatty acids and glycerol

29. Enzymes in Detergents?
• Special enzymes are found in detergents.
• Why do you think this is so?
o To help speed up the digestion of food stains
that usually contains carbohydrates, proteins
and fats which can then be washed out of the
clothes.

30. Actions of Digestive Enzymes
•Glucose, the end product of carbohydrate
digestion, is used for cellular respiration to
release energy.
Starch Maltose Glucose
Amylase Maltase

31. Actions of Digestive Enzymes
• Amino acids, the end products of protein
digestion, are used for growth and repair
of tissues, new cells and antibodies
formation.
Proteins
Amino acids
Protease

32. Actions of Digestive Enzymes
• Fatty acids & glycerol, the end products of
fat digestion, are used for cellular
respiration to release energy and for
forming cell membrane.
Fats Glycerol
Lipase
Fatty acids
+

33. The Human Digestive System
• Food is digested in our body through the
digestive system.
• The digestive system is made up a long tube
called the gut (or alimentary canal), which
starts at the mouth and ends at the anus.
• The gut is about nine metres long. The wall of
the gut is muscular, which allows food to move
along its length.

34. The Human Digestive System
• Other accessory organs are attached to
the tube, which supplies enzymes for
digestion of nutrients.
• These organs are also known as glands,
e.g. the salivary glands, liver and
pancreas.

35. The Human Digestive System
salivary gland
mouth cavity
oesophagus
stomach
salivary
glands
pancreas
colon
rectum
anus
large
intestine
liver
gall bladder
small intestine

36. 1st
Stop: Mouth

37. 1st
Stop: Mouth
• Both physical and chemical digestions take
place in the mouth.
• Physical digestion:
o Food is chewed in the mouth with the teeth.
o Chewing helps to cut and grind the food into
smaller pieces.
o This increases the surface area and allows
the food to be digested faster.

38. 1st
Stop: Mouth
• Chemical digestion:
o As food is chewed, salivary glands in the
mouth secrete saliva.
o Saliva serves two purposes:
• Wets the food, so that it is easier to swallow.
• Contains enzymes (amylase) to break down
starch into maltose.
o Digestion of starch:
• Starch Maltose
• There is no digestion of proteins and fats
in the mouth.
amylase

39. 1st
Stop: Mouth
• While chewing food, the tongue rolls the food
into small balls which are pushed to the back of
the mouth and squeezed into the oesophagus.
This is known as swallowing.
• Food stays in the mouth for about 20 seconds.

40. 1st
Stop: Mouth

41. 2nd
Stop: Oesophagus

42. 2nd
Stop: Oesophagus
• The oesophagus is a long muscular tube leading to the
stomach.
• Food moves slowly down to the stomach by process of
peristalsis (contracting and relaxing of the muscles).
• This is how food moves along the rest of the gut too.
• No digestion occurs in the oesophagus. However, the
digestion of starch by amylase continues as as saliva is
mixed with food.
• Food stays in the oesophagus for about 10 seconds.

43. 2nd
Stop: Oesophagus
Peristalsis is the involuntary
wave-like movement that pushes
the food into the stomach.

44. 3rd
Stop: Stomach

45. 3rd
Stop: Stomach

46. 3rd
Stop: Stomach
• The stomach is a muscular bag that lies in
the upper part of the abdomen.
• Both physical and chemical digestions
take place in the stomach.
• Physical digestion:
o Food is churned and mixed by muscles in
stomach wall.
o This movement also mixes the food well with
gastric juice for better digestion.

47. 3rd
Stop: Stomach
• Chemical digestion:
o Gastric juice is secreted by glands in the
stomach walls, into the stomach cavity. It
contains:
a) hydrochloric acid, which kills harmful bacteria
provides the acidic environment for proteases to
work.
b) protease which break down proteins into amino
acids
o Digestion of proteins:
• Protein Amino acids
• There is no digestion of carbohydrates or
fats in the stomach.
protease

48. 3rd
Stop: Stomach
• The cells lining the stomach walls produce a
thick layer of mucus to protect the stomach from
digesting itself and from the corrosive
hydrochloric acid.
• A thick mass of semi-liquid called chyme is
produced.
• Food stays in the stomach for 2 to 6 hours
before passing into the small intestine by
peristalsis.

49. 4th
Stop: Small Intestine

50. 4th
Stop: Small Intestine
• The small intestine is a long muscular tube,
which is about 6 m long.
• The liver and the pancreas are connected to the
small intestine.
• Digestion ends in the small intestine.

51. 4th
Stop: Small Intestine
Chyme is mixed with 3 fluids in the small
intestine to aid digestion:
Bile
Pancreatic juice
Intestinal juice

52. 4th
Stop: Small Intestine
• Physical digestion:
o The liver produces an alkaline yellowish-green fluid
called bile.
o Bile is stored in the gall bladder and has a duct (a
small tube) that carries bile into the small intestine.
o Bile does not contain digestive enzymes, but helps to
break up fats into smaller oil droplets in a process
known as emulsification.
o This increases the surface area of the oil and allows
the fats to be digested quickly by the lipases in the
pancreatic and intestinal juices.

53. 4th
Stop: Small Intestine
• Emulsification:

54. 4th
Stop: Small Intestine
• Chemical digestion:
o The pancreas produces alkaline pancreatic
juice and the intestine walls produces intestinal
juice.
o The juice contains the enzymes amylase,
protease and lipase.

55. 4th
Stop: Small Intestine
• The digestion of food in the small intestine are
as follows:
o Digestion of starch:
• Starch Maltose
• Maltose Glucose
o Digestion of small protein molecules
• Protein molecules amino acids
o Digestion of fats:
• Fat Fatty acids and glycerol
amylase
maltase
protease
lipase

56. 4th
Stop: Small Intestine
• Absorption is the process whereby digested food
molecules are taken into the body cells.
• Digested food passes through the wall of the small
intestine and into the blood vessels (capillaries)
which surround it.
• Water, vitamins and minerals are also absorbed.
• Food stays in the small intestine for about 5 hours.

57. 5th
Stop: Large Intestine

58. 5th
Stop: Large Intestine
The large intestine is about 1.5 m long.
Food that cannot be digested reaches here.
Undigested food is made up largely of fibres
which come from cellulose cell walls of plants.
Water and mineral salts are absorbed here in
the colon.
There is no enzymes or digestion here.

59. 5th
Stop: Large Intestine
• The mixture of undigested food and dead
bacteria is called faeces.
• Faeces are stored temporarily in the rectum.
• Most of the time, the muscles in the rectum stay
contracted.
• When the ring-like muscles between the rectum and
anus relax, faeces is passed out of the body through the
anus.
• This is known as defaecation or egestion.
• Food stays in the large intestine for up to 24 hours.

60. 5th
Stop: Large Intestine
• The anus is an opening at the opposite
end of an animal's digestive tract from the
mouth. Its function is to expel faeces.
(unwanted semi-solid matter).

61. Systems working together
• Each part of the digestive system carries out its
own function and work with other parts to make
sure food is digested and absorbed by the body.
• The digestive system also interacts with other
systems such as the muscular and blood
circulatory system.

62. Absorption of nutrients
• Digestion ends in the small intestine.
• The final products of digestion are glucose, amino acids,
fatty acids and glycerol, which are small and thus can
pass through its wall and into the bloodstream.
• Large molecules like starch and proteins cannot pass
through the walls of the small intestine.

63. Absorption of nutrients
• Food molecules pass through the intestine into the blood
by diffusion.

64. Absorption of nutrients
• To speed up the rate of absorption, the small intestine
has to increase its surface area.
• Adaptations:
1. Being long
• The small intestine is about 6 m.
1. Having a wall thickness of one cell
• This shortens the distance between the wall and
blood vessels, resulting in faster absorption.

65. Absorption of nutrients
• Adaptations:
3. Having microvilli
• The walls of the small intestine have many
finger-like projections called microvilli
(singular: microvillus).
• The microvilli provide a large surface area
for absorption of digested food molecules.
• Hence, digested food molecules can be
absorbed quickly into the blood.

66. Absorption of nutrients
• Villi
microvillus

67. Checkpoint Time
1. Label the parts of the Digestive System.
Part Name
1.
2.
3.
4.
5.
6.
7.

68. Checkpoint Time
1. Label the parts of the Digestive System.
Part Name
8.
9.
10.
11.
12.
13.
14.
15.

69. Checkpoint Time
3. State the end products that are obtained
in the digestion of :
a) Proteins__________________________
b) Fats_____________________________
c) Carbohydrates_____________________

70. Checkpoint Time
2. State the types of enzymes that help in
the digestion of :
a) Proteins__________________________
b) Fats_____________________________
c) Carbohydrates_____________________

71. Checkpoint Time
4. State the location(s) that the following
nutrients are digested in our body.
a) Proteins__________________________
b) Fats_____________________________
c) Carbohydrates_____________________

72. Food-Borne Diseases
• Foodborne illnesses are infections or irritations
of the gastrointestinal (GI) tract caused by food
that contain harmful bacteria, parasites, viruses,
or chemicals. The GI tract is a series of hollow
organs joined in a long, twisting tube from the
mouth to the anus.
• Common symptoms of foodborne illnesses
include vomiting, diarrhea, abdominal pain,
fever, and chills.

73. Preventing Food-Borne Diseases
• Foodborne illnesses can be prevented by
properly storing, cooking, cleaning, and handling
foods.
• Ways to prevent food-borne diseases:
o Raw and cooked perishable foods should be
refrigerated or frozen promptly.
o Foods should be cooked long enough to kill the
harmful bacteria that cause illnesses.

74. Preventing Food-Borne Diseases
• Ways to prevent food-borne diseases:
o Fruits and vegetables should be washed under
running water just before eating, cutting, or cooking.
o Raw meat, poultry, seafood, and their juices should
be kept away from other foods.
o Wash your hands with warm, soapy water before and
after handling raw meat, poultry, fish, shellfish or
eggs. Wash your hands after using the toilet.
o Utensils and surfaces should be washed with hot,
soapy water before and after they are used to prepare
food.