By Dilip Kumar Chandra

The processes of nutritionThe processes of nutrition

ingestion digestion absorption

assimilationegestion

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

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

Incissors Chisel-like & sharp

Biting & cutting food

Canine Pointed, curved & long

Killing prey & tearing flesh

Premolar & Molar

2 blunted points of

cusps

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:

Prevention of Tooth DecayPrevention of Tooth Decay 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

Movement of FoodMovement of FoodMouth:

Food chewed by teeth

mixed with saliva to form bonus

swallowed down the oesophagus through pharynx

oesophagustrachea

epiglottis

[Note: Epiglottis (a piece of cartilage) covers the entrance to the trachea while swallowing to prevent food going down into lungs.]

Movement of FoodMovement of FoodOesophagus:

Outer longitudinal & inner

circular muscles contract &

relax alternately (peristalsis)

Push food bolus to stomach

muscle contraction

muscle relaxation

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 sphincter

stomachspleenpyloric sphincter

coloncaecum

rectumanus

large intestine

pancreas

buccal cavity

tongue

tooth

trachea

liver

duodenumileum

appendix

small intestine

gall bladder

Mechanical Mechanical DigestionDigestion

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

Sites where Sites where digestion occurs:digestion occurs:

Alimentary canal (gut)

1. Buccal cavity

2. Stomach3. Small

intestine

How is food digested How is food digested

in these sites?in these 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

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 result

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 result 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 result 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 DigestionDigestionBREAK DOWN OF STARCH MOLECULES INTO MALTOSE MOLECULES BY SALIVARY AMYLASE (FROM SALIVARY GLANDS)

Starch

maltoses

salivary glands

Stomach Stomach (Physical Digestion) (Physical Digestion)

Stomach Entrance: Cardiac Sphincter

Stomach Exit: Pyloric Sphincter

Relaxation 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 Stomach (Chemical Digestion)(Chemical Digestion)

Stomach Stomach (Chemical Digestion)(Chemical 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

livergall bladder

• transport to duodenum through bile duct• take action in duodenum• bile pigment (excretory waste from breaking

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 emulsifies 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 vegetative

oil

shaking

shakingobserve

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 vegetative

oil

shaking

shakingobserve

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 lipases glycerol + 3 fatty acids

lipase

glycerol

fatty acids

lipidlipid

Intestinal Juice• produced and take action in

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

ileumduodenum

smallintestine

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 proteases

dipeptides 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

gradient for the diffusion of food

Absorption of food Absorption of food in ileumin ileum

lactealEpithelial cell

arteriole

venule

blood capaillaries

lymph vessel

villi

Structure of a VillusStructure of a Villus

glycerol

nucleusfatty acid

glucose

amino acid fat

capillarylacteal

Micro-villus

epithelial cell

Transverse Section of a villus showing food absorption

Transportation of absorbed Transportation of absorbed food in villifood 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 intestineLarge intestine caecum & appendix

◦no function in human ( small in ∴size)

colon

◦absorbs water & mineral salts◦failure to reabsorb water:

Diarrhoea rectum

◦stores faeces temporarily◦for egestion (defaecation)

caecumappendix

colon

rectum

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