1. DIGESTION
B M Subramanya Swamy M.Sc. B.Ed.
CIE Co ordinator & Examination Officer
Kanaan Global School
Jakarta
Indonesia
subramanyaswamy1591978@gmail.com

2. DIGESTION

3. Digestion
Process by which the body breaks down food
(carbohydrates, fats and proteins) into
simpler substances
These substances are absorbed and used by
cells in the body

4. Types of digestion
Types of digestion
Process
Mechanical

Mastication (chewing, mashing and breaking)
into smaller particles
 In the mouth, teeth cuts and grinds food.
Rolling action of tongue and secretion of
saliva rolls food into bolus
 Bolus is swallowed and transported through
pharynx to stomach by waves of rhythmic
contraction called peristalsis
Chemical

Changing food into smaller particles through
action of enzyme
 Involves hydrolysis (addition of water)
e.g. amylase converts carbohydrates into
simple sugars

5. THE HUMAN DIGESTIVE SYSTEM

6. THE WORKING OF HUMAN
DIGESTIVE SYSTEM

7. MOUTH
Functions : analysis material before swallowing, mechanical processing
by the teeth, tongue and palatal surfaces, lubricating, limited
digestion

8. TEETH
Functions :
 Grinding action (mastication) breaks down food
 Expose large area for enzyme action
child
adult

9. TONGUE
Functions :
 Rolls food into bolus

10. SALIVARY GLANDS
Secretions
Saliva contains:
 Water
Functions
Moisten and soften food
 As solvent and for hydrolysis
 Mucus
 Sticks food together to form bolus
maltose
 Salivary amylase  Starch


11. PHARYNX
Function : involuntary action pushes bolus into
oesophagus
Nasal cavity
Palate
Oral cavity
Tongue
Mandible
Pharynx

12. OESOPHAGUS
Functions :
• Walls made up of circular and longitudinal muscles
• Peristalsis transports food to the stomach
CARDIAC SPHINCTER
Function :
• Controls entry of food into the stomach

13. The swallowing process

14. Peristalsis
Characteristic
 Automatic
Length of alimentary canal made up circular and
longitudinal muscle
 Alternate contraction and relaxation of muscle

Result
Movement of food down the canal

15. Peristalsis

16. STOMACH
Secretions
Functions
Gastric juice
Muscular walls churn food into chyme
Stored food for 2 – 6 hours
Absorbs glucose and alcohol
Hydrochloric acid
Acidic medium (pH 1) for enzyme action
Kills bacteria brought in with food
Activates enzymes
Water
As solvent and for hydrolysis
Mucus
Protects stomach wall from acidic gastric juice
Lubricant for movement of food in the stomach
Pepsin
Protein
Rennin
Converts protein into insoluble curds (coagulates
milk) for hydrolysis of pepsin.
polypeptides

17. PHYLORIC SPHINCTER
Function : controls entry of food into duodenum

18. Stomach
Esophagus
Pylorus
Fundus
Body
Pyloric Den
Duodenum

19. Anatomy of the stomach

20. PANCREAS
Secretions
Functions
Pancreatic juice
Hydrolysis of food in duodenum
Amylase
Starch → maltose
Trypsin
Polypeptides → peptides
Lipase
Fats → fatty acids and glycerol
Water
As solvent for hydrolysis
Insulin
Excess glucose is converted to
glycerol in the liver

22. LIVER
Secretions
Dark green bile
Functions
 Provides alkaline pH
 Bile is stored in the gall bladder
 Emulsifies fats, provides increased
surface area for action of lipase
 Neutralise acidic chyme

23. Anatomy of the liver

24. Anatomy of the liver

25. SMALL INTESTINE
Secretion
Function
Intestinal juice
Final stage of digestion pH 8 (alkaline)
DUODENUM
Secretions
Erepsin
Lactase
Sucrase
Maltase
Water
Functions
Peptides → amino acids
Lactose → glucose and galactose
Sucrose → glucose and fructose
Maltose → sucrose
As solvent and for hydrolysis

26. JEJUNUM
Function : absorption of food
ILEUM
Function : absorption of food

27. The region of small intestine

28. The intestinal wall

29. The intestinal wall

30. The intestinal wall

31. LARGE INTESTINE
Function : absorption of water from undigested food
CAECUM AND APPENDIX
Function :
 Vestigial organs with no particular function
 Forms junction of small and large intestine
COLON
Secretion
Mucus
Function

Peristalsis compact undigested food to
form faeces
 Lubricates faeces and protects wall from
digestive juice

32. Large intestine

33. RECTUM
Function : stored faeces before defaecation
ANUS
Function : regulate emptying of rectum

34. What goes in must come out!

35. Comparison of human and herbivore digestive system
Human
Herbivore
Food
Carbohydrates, Mainly plant proteins
fats and proteins and cellulose
Alimentary canal
Stomach
Short
Simple
Long
Caecum
Very small
Large caecum with
cellulase to break down
cellulose to glucose

Several chambers
 Contains bacteria for
digestion of cellulose

36. ABSORPTION OF DIGESTED FOOD
 Nutrients from digested food must be moved from intestines
to the bloodstream
 This process is called absorption
 Almost all of the digested food is absorbed in the ileum
 The small intestine is about 6 -7 m long
 Water soluble end – products of digestion enter the blood
system by diffusion
 Fatty acids and glycerol are absorbed by the lacteals
 Once inside, fatty acids recombine with glycerol to form
globules of fat
 They are carried by the lymphatic system to the veins

37. Structure of the Villi in the Small Intestine

38. Structure of a villus

39. Adaptation of the ileum to absorb digested food
Features
Length
Adaptation
Longest part of the alimentary canal
Internal surface area Internal walls are folded to increase surface area for
absorption
Villi
Further increase surface area for absorption
Microvilli
Villus covered with epithelial cells
The plasma membrane of each cell has minute finger – like
projections (microvilli)
Further increase surface area
Movement
Villi move back and forth independently
Motion faster after meals
Absorption rate increases
Membrane
Absorption across membrane
Either by diffusion or active transport
capillary network
Dense capillary network close to epithelium
Carry away absorbed food particles quickly
Maintain concentration gradient between ileum and blood
capillaries to aid diffusion

40. ASSIMILATION
Assimilation  uptake and use of food within the body
Fate of end products of digestion
End – product
Fate
Glucose

Excess is converted to glycogen (insoluble granules)
and stored in the liver
 Converted back to glucose when body needs energy
and blood sugar level is low
 Further excess of glucose is stored as fats in the
adipose tissue
 Used in cellular respiration
Fats

Part of it stored as fats in adipose tissue
 Used in synthesis of cell membrane
 Utilised in respiration when glucose and glycogen is
used up
 Fats stored under skin and around organs act as
energy store and insulation

41. Fate of end products of digestion
End – product
Fate
Amino acids

Synthesis of proteins, enzymes and hormones
 For growth and development
 Excess amino acids are not stored in the body
 It is broken down and deaminated in the liver to form
ammonia and glycogen (glycogen is stored in the
liver)
Egestion

In the large intestine water and vitamins (synthesised
by bacteria) compact undigested food to form faeces
 Propelled along colon and rectum

42. LIVER
• Structure
 Large, reddish brown organ
 Located just beneath the diaphragm and
overlaps the stomach
 Plays an important role in metabolism,
homeostasis and excretion

43. • Anatomy

44. • Vessels associated with the liver
Vessels
Function
Hepatic portal vein

Hepatic artery
Carries oxygenated blood to liver
Hepatic vein
Carries blood containing waste
products away from liver
Blood capillaries of villi join to
form the hepatic portal vein
 Carries blood containing end
products of digestion from ileum
to liver

45. • Function of the liver
Function
Mode of action
Metabolism of glucose

Regulates the blood sugar concentration in
the body
 Excess sugars stored as glycogen granules
 This occurs in the presence of insulin
 When plasma sugar levels fall, glucagon
converts glycogen to glucose
Metabolism of amino acids

Regulates amount of amino acids in the
body
 Excess amino acids cannot be stored
 Converted during deamination into glucose
and urea
 Excess glucose is stored as glycogen
 Urea is excreted

46. Function
Mode of action
Production of bile

Produces bile, which is used in digestion
Storage of iron

Excretion of the bile
pigment

Synthesis of plasma
proteins

Storage of vitamins

Stores vitamin A and D
Reservoir for blood

Blood spaces and network of blood
capillaries hold a large volume of blood
Stores iron from breakdown of haemoglobin
 Used in the synthesis of new haemoglobin
Haemoglobin is broken down into bile
pigments biliverdin and bilirubin
 Both pigments are excreted into duodenum
as bile pigments
Synthesises plasma protein (fibrinogen,
serum globulin and serum) from amino acids
 They are responsible for the clotting of blood

47. Function
Mode of action
Source of heat energy

Metabolically active, producing a large
amount of heat energy to replace that lost by
the body
 Heat distributed to all parts of the body
Detoxification

Toxins produced bacteria in large intestines
are absorbed and converted to harmless
substances in the liver
 Liver removes about 95% of alcohol from
blood
 Alcohol oxidised in the liver to energy
 May also be converted to fats
 The other 5% lost as sweat, urine and
during breathing

48. DENTITION
STRUCTURE
Mechanical digestion is carried on in the mouth by the action
of the teeth and the tongue.

49. child
adult

50. Vertical section of molar
Crown
Enamel
Dentine
Gum
Pulp cavity containing
nerves and blood
vessels
Root
Jaw bone
Cementum

51. Tooth structure and function
Tooth structure
Components
Function
Enamel
Non – living layer of
hard calcium salts
Dentine
Softer bone – like layer Acts as a shock absorber
Pulp cavity
Contains tooth cells,
nerves and blood
capillaries
Tooth
Cement
Thin layer of bone –
like material
Covers
Root opening
Pathway for blood
capillaries and nerves
For
Protects
dentine
Forms a hard biting surface
cells divide to form
dentine
Supply food and oxygen to
cells
dentine of root
Holds root in socket
blood supply, growth and
replacement of tooth
Nerves carry messages to
and from brain

52. Tooth structure
Components
Function
Jaw bone with socket
Bone made of calcium Tooth fits into socket
phosphate
of jaw bone
Incisor
Single root
Sharp cutting edge
Biting of pieces of
food
Canine
Single root
Sharp and pointed
Tearing, seizing food
Premolar and molar
Wide and flat surface
Has cusps (points) or
ridges
Crushing and grinding
food

53. Different types of dental formula
Omnivore
Carnivore
Herbivore
Dental
formula
i:2
c:1
pm : 2
m :3
i:3
c :1
pm : 4
m: 2
i:0
c:0
pm: 3
m: 3
2
1
2
3
3
1
4
3
3
1
3
3
Mode of
nutrition
Plant and animal
Animal
Plant
Incisor
Chisel shaped
Sharp and pointed

Canine
About the same size as
incisors
Long, pointed, curved

Diastema
X
X
Upper incisor absent
 Small lower incisor,
bites against upper
horny pad
Upper canines
absent
 Lower canines have
sharp edges, bites
against upper horny
pad


54. Omnivore
Premolar / molar
Surface has small
cusps
Carnassial teeth
Carnivore
Surface has sharp,
pointed edges
X
Herbivore
Surface flattened
with small cusps

X
Feeding action

Upper and lower
 Upper and lower
jaw meet
jaw move up and
 Grind food with
down
lateral movements  Scissor – like
(side to side) of
action
lower jaw
 Tight jaw
attachment

Example
Adult human
Goat
Dog
Upper and lower
jaw meet
 Grind food with
lateral movements
(side to side) of
lower jaw
 Loose jaw
attachment

55. Tooth Decay
 Dental plaque is the result of bacteria acting on food or sugar
stuck on teeth
 Tartar is the hard deposit on the teeth caused by bacterial
plaque, calcium phosphate and calcium carbonate
 It leads to gum disease resulting in gum irritation and swollen
gum
 As the bacteria in plaque grow, it produces acid in the layer of
plaque
 This acid destroys the enamel and later, the dentine layer of
the teeth
 When the decay (cavity) spreads to the pulp cavity, the entire
tooth is affected
 The result is painful and swollen gum

56. Prevention of gum disease
Prevention
Action
Taking food rich in calcium,
phosphorous and vitamin D
Form strong teeth
Drinking water or using toothpaste
with added fluoride
Hardens tooth surface
Makes them less susceptible to
acids
Brushing teeth regularly
Remove food particles in teeth
Flossing teeth
Remove food lodged between
teeth
Reducing sugar in the diet
Reduce bacterial affect
Regular dental check up
Monitor health of teeth