What is digestion

1. Digestion in
Human Beings

2. Living organisms need food.
All food contains nutrients.
Nutrients are substances that provide the
energy and materials needed for growth,
repair and maintenance of cells and
regulation.
Nutrition is the process by which
organisms get food and break it down so it
can be used.
Nutrition

3. 26.1 Why We Need Food?
• We need food to:
o provide us with energy for our daily activities
like walking, and to maintain our body
temperature;
o maintain a healthy body;
o grow new cells and tissues; and
o repair worn out tissues.

4. 26.2 What is in the Food We
Eat?
• You need the essential nutrients in the food you
eat.
• 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.

5. Main types of nutrients
• There are three main types of nutrients:
carbohydrates, proteins and fats.
• Carbohydrates: Energy giving food
o The main carbohydrates in food are starch and
sugars. Starch can be found in rice, bread, noodles
and potatoes.
o Sucrose, glucose and maltose are also forms of
sugars. They can be found in fruits like bananas and
apples
o Cellulose is another type of carbohydrate, which can
be found in plants. Cellulose make up part of the fibre
(roughage) that cannot be digested by the body but
instead passed out from the body.

6. 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:
• build new cells for body growth and for the 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.

7. Main types of nutrients
• Fats
o Fats are large insoluble molecules that are
made up of glycerol and fatty acids.
o Fats provide us with twice as much energy as
carbohydrates.
o Fats can be found in food like butter and
cheese.
o Fats are stored under our skin to insulate our
body against too much heat loss.

8. Mineral Nutrients
• In the context of nutrition,
a mineral is a chemical
element required as an
essential nutrient by
organisms to perform
functions necessary for life.
However, the four major
structural elements in the
human body by weight, are
usually not included in lists
of major nutrient minerals.

13. What is a balanced diet?
A balanced diet is one that gives your body the
nutrients it needs to function correctly. To get the
proper nutrition from your diet, you should
consume the majority of your daily calories in:
•fresh fruits
•fresh vegetables
•whole grains
•legumes
•nuts
•lean proteins

15. Malnutrition produced by a severely inadequate amount of protein in the
diet.
Protein malnutrition, or kwashiorkor, is mostly found in people living in
geographical areas that have limited food resources. It's most seen in
children whose diets are low in protein and calories.
Delayed growth in children, a swollen stomach and frequent infections are
symptoms.
Treatment for kwashiorkor may include a slow increase in calories
followed by an increase in protein.
Kwashiorkor
Also called: protein malnutrition

18. 26.3 Why Must Food be
Digested?
• We can only use the nutrients in the food we eat
when they pass through the gut walls into the blood
vessels.
• Here, the nutrients can be carried through the
bloodstream to all parts of the body.
• The gut walls and blood vessels are made up of
cells.
• 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 small
molecules. They can pass through the cell
membranes easily and enter the bloodstream.

19. 26.3 Why Must Food be
Digested?
• But most major nutrients in food are large molecules
which cannot pass through the cell membranes.
• They must be broken down into molecules that are
small enough to pass through the cell membranes.
• This process is called digestion.
• Digestion is the breaking down of large, complex
food molecules into small, simpler molecules.
• Our body is able to carry out digestion by producing
complex proteins called enzymes.
• The enzymes involved in digestion are called
digestive enzymes.

20. 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.

21. 26.4 What are Enzymes?
• Enzymes are complex proteins that speed up
the rate of chemical reactions. Enzymes
remain 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.
• Substrates – substances that are
transformed with the help of enzymes

22. “Lock and key” hypothesis
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

23. “Lock-and-key” model of enzyme
action
• Emil Fischer – a nobel laureate in
Organic Chemistry in 1894
• “both the enzyme and the substrate
possess specific complementary
geometric shapes that fit exactly to each
other.”
• enzymes are never wasted, but are
always recycled

24. Digestion in Man

25. Digestion in Man
• mechanical phase
• chemical phase
• digested food is absorbed by the body in
coordination with the circulatory and
lymphatic systems
• undigested materials pass through the
anus into the external environment

26. Mechanical Phase of Digestion
• involves the change in the
physical properties of food.
• facilitated by peristalsis

27. Steps during mechanical digestion:
1.Mastication – cutting and chewing
of food with the use of the teeth
•four kinds of teeth

28. Steps during mechanical digestion:
2.Saliva produced from three pairs
of salivary glands moistens the
food

29. Steps during
mechanical digestion:
3.The tongue mixes
food with saliva. The
back of the tongue
secretes mucus which
makes the food easier
to swallow
•Deglutition – the act
of swallowing

30. Steps during mechanical digestion:
4.The food tube churns and mixes
food with digestive juices in the
stomach and small intestine
(kneading).

31. Chemical Phase
• there is a change in the chemical
composition of food

32. Types of digestive enzymes
•
•
A particular enzyme can only bring about one type of
chemical reaction.
For example, enzymes that break down proteins cannot
break down starch or fats.
Class of Acts on Digested products(s)
enzyme
Amylase
Maltase
Protease
Lipase
Starch
Maltose
Proteins
Fats
Maltose (a complex sugar)
Glucose (simple sugar)
Amino acids
Fatty acids and glycerol

33. Main Enzymes
• Carbohydrases – digest carbohydrates
(such as starches and double sugars)
that produces are simple sugars
• Proteases – digest proteins that
produces amino acids
• Lipase – digests fats which are also
called lipids that produces fatty acids
and glycerol

34. Chemical Digestion of
Carbohydrates
Organs, Glands
and Enzymes
Carbohydrates Digestion
Products
Salivary glands
Amylase or
ptyalin
Starch (amylum) Maltose
Pancreas
Amylase or
amylopsin
Starch (amylum) Maltose
Intestinal glands
Maltase Maltose Glucose
Sucrase Sucrose Glucose, fructose
Lactase Lactose Glucose, galactose

35. Chemical Digestion of Proteins
Site of
Digestion
Digestive
Juices
Substrate Products
Stomach Gastric juices
Hydrochloric acid
pepsin
rennin (in
infants)
Pepsinogen
Protein
Milk protein
Pepsin
Polypeptides
Polypeptides
Intestine Pancreatic and
Intestinal juice
trypsin
peptidases
Protein
Polypeptides
Polypeptides
Amino acids

36. Chemical Digestion of Fat
• Liver – largest gland in the body; secretes bile
which is stored in the gallbladder
• Bile is secreted by the time food is present in the
duodenum.
• Bile has no enzyme.
• Bile changes fat into tiny droplets through the
process of emulsification.
• 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.

37. Emulsification
Bile
Large oil drop
Small oil droplets

38. Absorption of Digested Food
• Absorption – the process by which
substances are taken in by the cells of
the food tube
• final digestion of food takes place in the
small intestine covered by very small
projects call villu, absorb digested food
• Two kinds of vessels: capillaries &
lacteals

39. Structure of a Villi

40. • Digested food in the form of molecules of
amino acids, simple sugars, fatty acids and
glycerol diffuse into the capillaries and
reach the blood.
• Molecules of fatty acids diffuse into the
lacteals and reach another circulating fluid,
the lymph.
• food tube  villu  lymph & blood
(circulatory system)
• circulating liquids distribute the digested
food to all cells of the body.
Absorption of Digested Food

41. • Stomach – absorbs alcohol, water and
minerals
• Large intestine – absorbs excess water
Absorption of Digested Food

42. Synthesis
• How does the digestive system interact
with the excretory, respiratory and
circulatory system?
• What is the importance of food and
digestion in humans?

43. Assignment
B.Study for a quiz on Tuesday, Feb. 16.
Topic: Digestion in Human Beings
C. Long Test on Thursday, Feb. 18.
Topics: Modern Periodic Table – Digestive System
A. What are the diseases of the digestive system?
Disease Symptoms Cause Treatment

44. 26.5 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).
• The gut is about nine metres long. The wall of
the gut is muscular, which allows food to move
along its length.
• Food enters the body through the mouth, and
undigested food leaves the body through the
anus.

45. 26.5 The Human Digestive
System
• Glands connected to the gut are organs
which produce special juices containing
enzymes.
• These glands are the salivary glands,
liver and pancreas.

46. 26.5 The Human Digestive
System
salivary gland
mouth cavity
oesophagus
salivary
glands
stomach
pancreas
colon
rectum
anus
large
intestine
liver
gall bladder
small intestine

47. The mouth
food
oesophagus
windpipe

48. The mouth
• Food is chewed in the mouth with the
teeth.
• Chewing helps to cut and grind the food
the smaller pieces.
• This increases the surface area and
allows the food to be digested faster.
• As food is chewed, salivary glands in the
mouth secrete saliva.

49. The mouth
• Saliva serves two purposes:
o Wets the food, so that it is easier to swallow.
o Digests starch into sugars with the help of an
enzyme called salivary amylase.
• While chewing food, the tongue rolls the
food into small balls when are pushed to
the back of the mouth and squeezed into
the oesophagus. This is known as
swallowing.

50. The oesophagus
Muscles
contract to
push the food
ball down.
Muscles relax,
and the tube
widens for food to
move.

51. The oesophagus
• The oesophagus is a long muscular tube
leading to the stomach.
• By contracting and relaxing, the muscles help to
push the food down to the stomach.
• 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
may continue as the food moves to the stomach.

52. The stomach
stomach

53. The stomach
•
•
•
•
•
•
The stomach is a muscular bag that lies in the upper
part of the abdomen.
Its muscles contract and relax, causing food to break
up into even smaller pieces.
This movement also mixes the food well with gastric
juice for better digestion.
Gastric juice is secreted by glands in the stomach
walls, into the stomach cavity. It contains:
o proteases which digest proteins; and
o hydrochloric acid, which helps proteases to work.
Hydrochloric acid kills any bacteria in the food.
Food stays in the stomach for a few hours before
passing into the small intestine, bit by bit.

54. The small intestine, liver and pancreas
gall bladder
liver
small intestine
pancreas

55. The 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.
• Food is mixed with 3 fluids in the small intestine
to aid digestion:
o Intestinal juice from the walls of the intestine. It
contains the enzymes maltase, proteases and
lipases.
o Pancreatic juice from the pancreas.
o Bile from the liver.

56. Pancreas
• The pancreas produces alkaline pancreatic
juice.
• The juice contains the enzymes amylase,
protease and lipase.
• The digestion of food in the small intestine are
as follows:
o Digestion offats:
Fatty acids and glycerol
•Fat lipase

57. Pancreas
• The digestion of food in the small intestine are
as follows:
o Digestion ofstarch:
Maltose
amino acids
•Starch amylase in
pancreatic juice
• Maltose maltase Glucose
o Digestion of small protein molecules
• Protein molecules protease

58. Liver
•
•
•
•
•
The liver produces a yellowish-green fluid called bile.
Bile is stored in the gall bladder.
The gall bladder has a duct (a small tube) that carries
bile into the small intestine.
Bile does not contain digestive enzymes, but helps to
break up fast into smaller oil droplets in a process known
as emulsification.
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.

59. Emulsification
Bile
Large oil drop
Small oil droplets

60. Absorption in the small intestine
• The small intestine allows only small molecules
like sugar and amino acids to pass through its
wall and into the bloodstream.
• Large molecules like starch and proteins cannot
pass through the walls of the small intestine.
• Digestion ends in the small intestine.
• The final products of digestion are glucose,
amino acids, fatty acids and glycerol.

61. Absorption in the small intestine
• After digestion, the smaller digested food
molecules can pass through the wall of the small
intestine and into the bloodstream.
• Undigested matter is mostly made up of fibre.
• Together with water and mineral salts, the
undigested food passes into the large intestine.
• Fibre can be found in vegetables. It is important
for the gut muscles to move the food along the
gut.

62. The large intestine
large intestine
rectum
anus

63. The large intestine
• The large intestine is about 1.5 m long.
• Its function is to absorb water and mineral
salts.
• This takes place in the colon.
• What is left now is a nearly solid waste
called faeces.
• This is temporarily stored in the rectum,
before being expelled through the anus is
a process called egestion.

64. Miscellaneous
• http://kidshealth.org/kid/body/digest_noSW.html
• http://www.ahealthyme.com/topic/digestivesystem
• http://hopkins-gi.org/multimedia/database/intro_250_
• http://yucky.discovery.com/noflash/body/pg000008.h
• http://hes.ucf.k12.pa.us/gclaypo/digestive_system.ht