The processes of The processes of nutritionnutrition

ingestion digestion absorption

assimilation

egestion

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

external structure internal structure

enamel

dentine

blood capillaries

nerve fibres

cement

jaw bone

gum

crown

neck

root

pulp cavity(pulp tissues)

Teeth StructuresTeeth Structures

enamelcrown

neck

root

- outermost & hardest layer covering the crown (97% Ca, 3% organic matter)

external structure

Teeth StructuresTeeth Structuresinternal

structure

dentinecrown

neck

root

- hard like bone but softer than enamel

external structure

Teeth StructuresTeeth Structuresinternal

structure

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

crown

neck

root- anchor the tooth in its position

cement

external structure

Teeth StructuresTeeth Structuresinternal

structure

Teeth StructuresTeeth Structures

gumcrown

neck

root

jaw bone

Periodontal membrane

- fibres attaching tooth to jawbone

external structure internal structure

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)

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

DentitionDentition• dental formula• e.g. Human (permanent set) =

2123 2123

• other dentitions :

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:

Effect of Acid on a Tooth

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

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

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

Prevention of Tooth DecayPrevention of Tooth Decay

• use dental floss (to remove food remain between teeth)

• form a good tooth-cleaning habit by using dental disclosing agent

Prevention of Tooth Prevention of Tooth DecayDecay

• 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

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.]

Movement of Movement of FoodFood

muscle contracti

onmuscle

relaxation

Oesophagus:

Outer longitudinal & inner circular muscles contract & relax alternately (peristalsis)

Push food bolus to stomach

A process by which large food molecules are broken down into smaller pieces

Why is digestion Why is digestion needed?needed?

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.)

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

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

Mechanical DigestionMechanical Digestion

Chewing : break down food into smaller pieces by teeth to increase the surface area for enzyme action (physical digestion)

Chemical DigestionChemical Digestion

Enzymatic Reactions which

digest food into simpler

chemical forms

To show the Differential Permeability of Dialysis

Tubing to Starch & Glucose

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

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

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

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

Where is food Where is food digested?digested?

Sites where digestion Sites where digestion occurs:occurs:Alimentary canal (gut)

1. Buccal cavity

2. Stomach3. Small

intestine

How is food How is food

digested in these digested in these

sites?sites?

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

Action of Amylase

on Starch

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

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

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

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

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

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

Chemical Chemical DigestionDigestion

break down of starch molecules into maltose molecules by salivary amylase (from salivary glands)

Starch

maltoses

salivary glands

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

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

• 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)

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)

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

BileBile• with bile salts (not

an enzyme)• produced in liver• stored in gall

bladder

duodenum

liver

gall bladder

• transport to duodenum through bile duct

• take action in duodenum• bile pigment (excretory waste from brea

king down of haemoglobin)liver

gall bladder

BileBile

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

Effect of Bile Salt on Fat

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

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

Pancreatic JuicePancreatic Juice

• produced in pancreas

• action in duodenum Pancreas

Duodenum

Pancreatic JuicePancreatic Juice

- contain enzymes of 3 categories:

1. Carbohydrase (Amylase) 2. Proteases 3. Lipases- provide alkaline medium for enzymes to work

pancreatic amylasestarch maltose

starch maltose

pancreatic proteases

proteinDipeptides/ polypeptides

protein

dipeptide

protease

pancreatic lipasesglycerol + 3 fatty acids

lipase

glycerol

fatty acids

lipid

lipid

Intestinal Juice•produced and take

action in small intestine (duodenum & ileum) to complete the digestion of food

ileum

duodenumsmallintestine

Digestion in ileumDigestion in ileum

Intestinal JuiceIntestinal Juice- Contain enzymes of 2 categories: 1. Carbohydrase (eg. maltase) 2. Protease

disaccharides(eg. maltose)

monosaccharides(eg. glucose)

carbohydrasedisaccharide

intestinal carbohydrase

monosaccharide

intestinal proteasesdipeptides amino acids

proteaseamino acid

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

• 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

lactealEpithelial cell

arteriole

venule

blood capaillaries

lymph vessel

villi

Structure of a VillusStructure of a Villus

glycerol

nucleus

fatty acid

glucose

amino acid fat

capillarylacteal

Micro-villus

epithelial cell

Transverse Section of a villus showing food absorption

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

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

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)

Digestive System in RabbitDigestive System in Rabbit

Alimentary canal of a rat

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

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

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

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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