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The processes of The processes of nutritionnutrition
ingestion digestion absorption
assimilation
egestion
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IngestionIngestion
•a process by which food is taken in through the mouth
•a reflex action which is involuntary
• it occurs when the food is put at the posterior position of the tongue
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external structure internal structure
enamel
dentine
blood capillaries
nerve fibres
cement
jaw bone
gum
crown
neck
root
pulp cavity(pulp tissues)
Teeth StructuresTeeth Structures
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enamelcrown
neck
root
- outermost & hardest layer covering the crown (97% Ca, 3% organic matter)
external structure
Teeth StructuresTeeth Structuresinternal
structure
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dentinecrown
neck
root
- hard like bone but softer than enamel
external structure
Teeth StructuresTeeth Structuresinternal
structure
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crown
neck
root
blood capillaries
nerve fibres
pulp cavity(living tissues)
- supply food & oxygen for growth & maintaining alive
- produce sensation of pain when stimulated
external structure
Teeth StructuresTeeth Structuresinternal
structure
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crown
neck
root- anchor the tooth in its position
cement
external structure
Teeth StructuresTeeth Structuresinternal
structure
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Teeth StructuresTeeth Structures
gumcrown
neck
root
jaw bone
Periodontal membrane
- fibres attaching tooth to jawbone
external structure internal structure
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Two sets of teethTwo sets of teeth• milk teeth
– in young child before approximately six years old
– without molar– 20 teeth
• permanent teeth– no replacement for lost– 32 teeth (including wisdom
teeth)
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Types of teethTypes of teethTypes
of Teeth
Shape Functions
IncisorChisel-like & sharp
Biting & cutting
food
CaninePointed, curved &
long
Killing prey & tearing
flesh
Premolar &
Molar
2 blunted points of cus
ps
Crushing & grinding
food
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DentitionDentition• dental formula• e.g. Human (permanent set) =
2123 2123
• other dentitions :
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Tooth decayTooth decay
• bacteria together with food remains,– forming plaque
•bacteria produce acid which dissolves the enamel of tooth
•acid penetrates into dentine•bacteria infect pulp cavity•causing toothache
Causes:
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Effect of Acid on a Tooth
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What do you find on the covered and uncovered parts of the tooth ?Ans: The acid dissolves the exposed enamel and le
aves a small hole on the uncovered part, but holes do not appear on the covered part.
tooth covered with wax
dilute hydrochloric acid
probingscraping
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Does the acid take place in causing tooth decay ?Ans: Actually the acid produced by bacteria in the
mouth is not very strong. Tooth decay is due to bad habits over a long period of time.
tooth covered with wax
dilute hydrochloric acid
probingscraping
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Prevention of Tooth Prevention of Tooth DecayDecay
• have a balanced diet (include Ca, P & vitamin D)
• adding fluoride in water to strengthen the enamel of our teeth(NOT chlorine which kills bacteria in water)
• avoid sugary food & drinks between meals
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Prevention of Tooth DecayPrevention of Tooth Decay
• use dental floss (to remove food remain between teeth)
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• form a good tooth-cleaning habit by using dental disclosing agent
Prevention of Tooth Prevention of Tooth DecayDecay
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• brush our teeth at least twice a day
• replace your toothbrush when it wears out
• do not bite hard materials
• have a dental check-up at least once a year
Prevention of Tooth Prevention of Tooth DecayDecay
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Movement of Movement of FoodFood
oesophagustrachea
epiglottis
Mouth:Food chewed by teeth mixed with saliva to form bon
us swallowed down the oesophag
us through pharynx
[Note: Epiglottis (a piece of cartilage) covers the entrance to the trachea while swallowing to prevent food going down into lungs.]
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Movement of Movement of FoodFood
muscle contracti
onmuscle
relaxation
Oesophagus:
Outer longitudinal & inner circular muscles contract & relax alternately (peristalsis)
Push food bolus to stomach
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A process by which large food molecules are broken down into smaller pieces
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Why is digestion Why is digestion needed?needed?
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Because:Because:
food pieces and their molecules (e.g. starch, protein & fat) are usually too large to pass through the wall of our body for absorption(Note: Simple sugars, water, vitamins & minerals are small enough to be absorbed immediately.)
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So,So,
food pieces should be broken down into smaller pieces and then into substances with molecular size which is small enough to be absorbed
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Human Digestive SystemHuman Digestive System
salivary glandsepiglottis
oesophagusdiaphragmcardiac sphincterstomachspleenpyloric sphinctercoloncaecumrectumanus
large intestine
pancreas
buccal cavity
tongue
tooth
trachea
liver
duodenumileum
appendix
small intestin
e
gall bladder
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Mechanical DigestionMechanical Digestion
Chewing : break down food into smaller pieces by teeth to increase the surface area for enzyme action (physical digestion)
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Chemical DigestionChemical Digestion
Enzymatic Reactions which
digest food into simpler
chemical forms
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To show the Differential Permeability of Dialysis
Tubing to Starch & Glucose
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Why is it necessary to rinse the dialysis tubing with tap water ?
Ans: In order to remove any starch and glucose that may remain on the outside of the dialysis tubing.
Starch-glucose mixture
thread
Test for glucose
Test for starch
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Which food substance is present in water surrounding the dialysis tubing 30 minutes after the beginning of the experiment ? Explain your answer.Ans: Glucose. As dialysis tubing is selectively perme
able, starch molecules are too large to pass through the holes in the tubing...
Starch-glucose mixture
thread
Test for glucose
Test for starch
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Which food substance is present in water surrounding the dialysis tubing 30 minutes after the beginning of the experiment ? Explain your answer.Ans: Only glucose molecules are small enough to p
ass through the dialysis tubing in this experiment.
Starch-glucose mixture
thread
Test for glucose
Test for starch
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Which part of the body is presented by the dialysis tubing and the water in the boiling tube respectively ?Ans: Ileum and blood are represented by the dialy
sis tubing and water respectively.
Starch-glucose mixture
thread
Test for glucose
Test for starch
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Where is food Where is food digested?digested?
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Sites where digestion Sites where digestion occurs:occurs:Alimentary canal (gut)
1. Buccal cavity
2. Stomach3. Small
intestine
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How is food How is food
digested in these digested in these
sites?sites?
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Digestion in Buccal CavityDigestion in Buccal Cavity• There are 3 pairs of salivary
glands• Saliva contains water, mucus &
enzyme (amylase)• Water: moistens dry food• Mucus: lubricates food• Amylase: digests about 5% of
starch in mouth
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Action of Amylase
on Starch
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What are the results of the iodine test and Benedict’s test for tube A ?Ans: The result of iodine test is negative while the r
esult of the Benedict’s test is positive.
A B Cthermometer
water bath at 37
℃
after 30 minutes
each test tube
test with Benedict
’s solution
test sample
with iodine
solution
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What are the results of the iodine test and Benedict’s test for tube B ?Ans: The result of iodine test is positive while the r
esult of the Benedict’s test is negative.
A B Cthermometer
water bath at 37
℃
after 30 minutes
each test tube
test with Benedict
’s solution
test sample
with iodine
solution
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What are the results of the iodine test and Benedict’s test for tube C ?Ans: The result of iodine test is positive while the r
esult of the Benedict’s test is negative.
A B Cthermometer
water bath at 37
℃
after 30 minutes
each test tube
test with Benedict
’s solution
test sample
with iodine
solution
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Why is the temperature of the water bath set at 37 ℃ ?Ans: Because enzymes work best at 37 ℃.
A B Cthermometer
water bath at 37℃
after 30 minutes
each test tube
test with Benedict
’s solution
test sample
with iodine
solution
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What is the action of amylase on starch ?Ans: Amylase is an enzyme in saliva which helps
to digest starch into maltose.
A B Cthermometer
water bath at 37
℃
after 30 minutes
each test tube
test with Benedict
’s solution
test sample
with iodine
solution
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What is the effect of boiling on amylase ?Ans: Amylase denatured after boiling.
A B Cthermometer
water bath at 37
℃
after 30 minutes
each test tube
test with Benedict
’s solution
test sample
with iodine
solution
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Chemical Chemical DigestionDigestion
break down of starch molecules into maltose molecules by salivary amylase (from salivary glands)
Starch
maltoses
salivary glands
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Stomach Stomach (Physical (Physical Digestion) Digestion) Stomach Entrance: Cardiac
Sphincter
Stomach Exit: Pyloric SphincterRelaxation of cardiac sphincter &
contraction of pyloric sphincter enable
storage of food in stomach for a longer
period of time
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Stomach (Physical Stomach (Physical Digestion) Digestion)
Squeezing & churning actions of stomach break down the partly digested food into smaller pieces which forms a semi-fluid called Chyme
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• digestive juice : gastric juice (pH 2) (by gastric glands)
• enzymes : protease
• break down of protein molecules into polypeptides or dipeptides
Stomach (CheStomach (Chemical Digestion)mical Digestion)
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Stomach (CheStomach (Chemical Digestion)mical Digestion)•hydrochloric acid :
–to provide acidic medium for maximum activity of enzyme
–to kill bacteria–to stop the activity of salivary amylase
(Stomach wall secretes a mucous layer to cover its inner surface: prevents autodigestion by protease)
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Small Intestine Small Intestine (mainly chemical (mainly chemical digestion)digestion) Digestion of various food substances by several kinds of digestive juices Digestive juices found
in small intestine:
1. Bile2. Pancreatic juice3. Intestinal juice
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BileBile• with bile salts (not
an enzyme)• produced in liver• stored in gall
bladder
duodenum
liver
gall bladder
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• transport to duodenum through bile duct
• take action in duodenum• bile pigment (excretory waste from brea
king down of haemoglobin)liver
gall bladder
BileBile
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BileBile- contain bile salts which emulsify lipids
into smaller droplets without chemical change ( ∴ NOT digest fats)
- provide alkaline medium for enzymes to work
oil
oil droplets
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Effect of Bile Salt on Fat
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What happens to the mixtures in tubes A & B ?Ans: In tube A, bile salt e
mulsifies the vegetable oil to droplets. In tube B, the oil floats on top of water since oil and water do not mix well.
1cm3 of vegetati
ve oil
shaking
shakingobserv
e
observe
10 drops of bile salt solution
A
B
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What is the action of bile salt on oil ?
Ans: The bile salt reduces the surface tension of oil and emulsifies oil to droplets.
1cm3 of vegetati
ve oil
shaking
shakingobserv
e
observe
10 drops of bile salt solution
A
B
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Pancreatic JuicePancreatic Juice
• produced in pancreas
• action in duodenum Pancreas
Duodenum
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Pancreatic JuicePancreatic Juice
- contain enzymes of 3 categories:
1. Carbohydrase (Amylase) 2. Proteases 3. Lipases- provide alkaline medium for enzymes to work
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pancreatic amylasestarch maltose
starch maltose
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pancreatic proteases
proteinDipeptides/ polypeptides
protein
dipeptide
protease
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pancreatic lipasesglycerol + 3 fatty acids
lipase
glycerol
fatty acids
lipid
lipid
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Intestinal Juice•produced and take
action in small intestine (duodenum & ileum) to complete the digestion of food
ileum
duodenumsmallintestine
Digestion in ileumDigestion in ileum
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Intestinal JuiceIntestinal Juice- Contain enzymes of 2 categories: 1. Carbohydrase (eg. maltase) 2. Protease
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disaccharides(eg. maltose)
monosaccharides(eg. glucose)
carbohydrasedisaccharide
intestinal carbohydrase
monosaccharide
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intestinal proteasesdipeptides amino acids
proteaseamino acid
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AbsorptionAbsorption• stomach : absorbs alcohol
& drugs
• ileum : absorbs digested food(with a large amount of water)(∴ it absorbs the largest amount of water)
• colon : absorbs water & mineral salts
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• It is long, with many finger-like villi– to provide large surface area
for absorption of digested food• It has thin wall
– to decrease the diffusion distance for easy diffusion of food
• It has well developed transport system (blood capillaries & lacteal)– to maintain high concentration gra
dient for the diffusion of food
Absorption of Absorption of food in ileumfood in ileum
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lactealEpithelial cell
arteriole
venule
blood capaillaries
lymph vessel
villi
Structure of a VillusStructure of a Villus
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glycerol
nucleus
fatty acid
glucose
amino acid fat
capillarylacteal
Micro-villus
epithelial cell
Transverse Section of a villus showing food absorption
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Transportation of absorTransportation of absorbed food in villibed food in villi
• blood capillaries : absorb glucose & amino acids (which are smaller molecules)
• lacteal : absorb fatty acids & glycerol (which are larger molecules)
– transport fats (glycerol & fatty acids recombine together after being absorbed)
• involve both diffusion & active transport
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Large Large intestineintestine• caecum & appendix– no function in human (∴ small i
n size)• colon
– absorbs water & mineral salts– failure to reabsorb water: Diarrh
oea• rectum
– stores faeces temporarily– for egestion (defaecation)
caecumappendix
colon
rectum
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Caecum & Appendix in RabbitCaecum & Appendix in RabbitIt is very large in size
to store plant for long time for bacteria to secrete cellulase to digest cellulose to glucose
The rabbit should re-ingest faeces for absorption of glucose( ∵ absorption of food only proceeds in ileum)
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Digestive System in RabbitDigestive System in Rabbit
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Alimentary canal of a rat
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EgestionEgestion(Defaecation)(Defaecation)
removal of undigested or unabsorbed food substances
faeces: semi-solid brown mass (includes undigested food, dead & live bacteria)
faeces is temporarily stored in rectum & eventually be expelled through anus
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AssimilationAssimilation• a process which absorbs food
incorporated as a part of body cells
• digested food is transported to liver by hepatic portal vein
• lacteal transports fat into lymph vessels & then into the bloodstream
• malfunction of pancreas to secrete insulin: Diabetes
diabetes
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Functions of Functions of LiverLiver
• changes excess blood glucose to glycogen & stores in liver to regulate blood glucose level
• deaminates excess amino acids – to urea which is excreted
by kidney– to glycogen for energy storag
e
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Functions of Functions of LiverLiver
• stores vitamins A, D, E, K (which are fat soluble) iron & glycogen
• changes Carotene to Vitamin A
• secretes bile for fat emulsification
• Detoxification:
turns mild toxins into harmless substances
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