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Unit 5: Animal Nutrition 5.1-NUTRIENTS, 5.2 –DIET, 5.3-WORLD FOOD SUPPLIES, 5.4-HUMAN ALIMENTARY CANAL,
5.5-CHEMICAL DIGESTION, 5.6-ABSORPTION AND ASSIMILATION
SUFEATIN SURHAN BIOLOGY MSPSBS 2012
SYLLABUS CHECKLIST:
Candidates should be able to: (a) list the chemical elements that make up:
carbohydrates; fats; proteins;
(b) describe tests for: starch (iodine in potassium iodide); reducing sugars (Benedict’s solution); protein (Biuret test); fats (ethanol emulsion test);
(c) list the principal sources of, and describe the dietary importance of carbohydrates, fats, proteins, vitamins (C and D only), mineral salts (calcium and iron only), fibre (roughage) and water;
(d) describe deficiency symptoms of vitamins C and D and mineral salts calcium and iron; (e) understand the concept of a balanced diet; (f) explain why diet, especially energy intake, should be related to age, sex and activity of an individual; (g) state the effects of malnutrition in relation to starvation, heart disease, constipation and obesity; (h) discuss the problems that contribute to famine (unequal distribution of food, drought and flooding,
increasing population); (i) identify the main regions of the alimentary canal and the associated organs: mouth, salivary glands,
oesophagus, stomach, duodenum, pancreas, gall bladder, liver, ileum, colon, rectum and anus; (j) describe the main functions of these parts in relation to ingestion, digestion, absorption, assimilation and
egestion of food, as appropriate; (k) identify the different types of human teeth and describe their structure and functions; (l) state the causes of dental decay and describe the proper care of teeth; (m) describe peristalsis; (n) explain why most foods must be digested; (o) describe:
digestion in the alimentary canal; the functions of a typical amylase, protease and lipase, listing the substrates and end-products;
(p) describe the structure of a villus, including the roles of capillaries and lacteals; (q) describe the significance of villi in increasing the internal surface area; (r) state the function of the hepatic portal vein as the route taken by most of the food absorbed from the small
intestine; (s) state:
that large molecules are synthesised from smaller basic units: glycogen from glucose; proteins from amino acids; lipids (fats and oils) from glycerol and fatty acids;
the role of the liver in the metabolism of glucose and amino acids; the role of fat as a storage substance; that the formation of urea and the breakdown of alcohol occur in the liver.
SUF/BIO/MSPSBS/2012 2 OF 15
NUTRIENTS
Nutrients are chemical substances in food that
provide energy and materials needed by the body.
Food is a store of raw materials and potential
energy. An organism needs food:
as a source of energy for the chemical
reactions that take place in its body to keep it
alive and active.
for growth: to provide the substances needed
for making new cells and tissues, to repair and
replace worn and damaged tissues, and for
reproduction.
for making important chemicals in the body,
e.g. haemoglobin, enzymes, hormones,
antibodies, etc.
for maintaining health.
Food is made up of:
nutrients: carbohydrates, fats and oils,
proteins, vitamins, minerals and water;
fibre (roughage).
Of theses, only minerals and water are inorganic,
the rest are organic, i.e. carbon compounds.
Carbohydrates, fats and oils, and proteins are
required in large quantities as they supply energy
and materials to the living organism.
CARBOHYDRATES
Carbohydrates are made up of the elements carbon,
hydrogen and oxygen.
The hydrogen and oxygen atoms are present in the
ratio 2:1 in each carbohydrate molecule (the same
ratio in which they are present in water).
Carbohydrates may be classified into:
1. monosaccharides,
2. disaccharides and
3. polysaccharides.
Monosaccharides (Mono:One, Saccharides:Sugar)
Monosaccharides are simple sugars with the formula
C6H12O6 but their atoms are arranged differently
within the molecules. These different arrangements
give the sugars different chemical and biochemical
properties.
They are soluble in water.
Examples of monosaccharides are:
1. Glucose; it is the energy source of both plants
and animals cells respiration.
2. Fructose; it is found in honey, tree fruits,
berries, melons and some root vegetables.
3. Galactose; it is found in dairy products and
sugar beets.
They produce a brick-red precipitate of
copper(I)oxide when boiled with Benedict’s
solution. Sugars with this property are called
reducing sugars.
Disaccharides (Di:Two, Saccharides:Sugar)
Disaccharides are complex sugars with the formula
C12H22O11.
They are soluble in water.
They are formed when two monosaccharides are
combined by a process of removing water called
condensation.
Examples are:
1. Maltose (malt sugar; found in germinating
grains) made up of condensing two
molecules of glucose.
2. Sucrose (cane sugar) made up of condensing
a molecule of glucose and fructose.
3. Lactose (milk sugar) made up of condensing
a molecule of glucose and galactose.
Maltose and lactose are reducing sugars while
sucrose is not.
Polysaccharides (Poly:Many, Saccharides:Sugar)
Polysaccharides are macromolecules which are
made up of thousands of simple sugar units.
They are insoluble in water.
Polysaccharides are produced by the condensation
of many glucose units to form a long molecule but in
each, the glucose units are linked in a different
way.
Examples of polysaccharides are:
1. Starch; the storage form of glucose in green
plants. Cereals, potatoes, yam and tapioca are
rich sources of starch.
2. Glycogen; the storage form of glucose in
animals.
3. Cellulose; forms the cell walls in plants.
Mammals cannot digest cellulose but herbivores
have bacteria in their intestines to digest it. In
other mammals, cellulose forms fibre in the
diet.
SUF/BIO/MSPSBS/2012 3 OF 15
They can be broken down to smaller molecules by
hydrolysis using acid or enzymes.
Glycogen and starch are suitable as storage
materials because:
They are insoluble in water and so do not
change the osmotic pressure in the cells.
They are large molecules which are unable to
diffuse through the cell membranes.
They are easily hydrolysed to glucose when
needed and so is ideal as a stand-by source of
energy.
The molecules have compact structures so they
occupy less space.
They are inactive.
Dietary Importance of carbohydrates
As a substrate for respiration, to provide energy for
cell activities (1g yields 17kJ of energy);
To form supporting structures, eg. cell walls in
plants;
To be converted into other organic compounds such
as amino acids and fats;
For the formation of nucleic acids, eg. DNA;
To synthesise lubricants, eg. mucus, which consists
of a carbohydrate and a protein; and
To synthesise the nectar in some flowers. Nectar is
a sweet liquid that plants produce to attract
insects.
LIPIDS
Fats and oils are made up of the elements carbon,
hydrogen and oxygen but they contain very little
oxygen unlike carbohydrates.
Fats are made up of fatty acids and glycerol joined
up as shown:
They are all insoluble in water.
There are two types of fats:
1. Saturated fats (Animal fats).
Contain saturated fatty acids.
Solids at room temperature.
Examples are butter and lard.
Bad for health.
2. Unsaturated fats (Vegetable fats).
Contain unsaturated fatty acids.
Liquids at room temperature.
Examples are corn oil and palm oil.
Good for health.
Dietary sources of fats
Animal fats: meat, milk, lard, butter and egg yolk.
Plant fats: found as oils in nuts and seeds.
Dietary importance of fats
As a source of energy (1g yields 39kJ of energy);
To form part of the cell surface membrane;
As solvents for fat-soluble vitamins (A, D, E and K)
and some hormones;
As an insulation to prevent excessive heat loss from
the skin of mammals;
As shock absorber to protect internal organs from
physical damage;
To prevent water loss from the skin surface (in
human)
Secretion of sebum (oily substance from
sebaceous glands) over the skin surface provides
a waterproof layer
Rate of water loss from evaporation decreases
For buoyancy in aquatic animals (blubber in
whales).
PROTEINS
Proteins are made up of the elements carbon,
hydrogen, oxygen and nitrogen. Often, sulphur
and phosphorus are also present.
They are made up of basic units called amino acids
linked together by condensation to form polypeptide
chains.
These polypeptide chains are folded and twisted to
form large, complex structures.
There are twenty-two types of naturally occurring
amino acids.
In each protein, some or all the amino acids are
present in different numbers and order so that each
protein is unique.
The essential amino acids are amino acids that
cannot be made in our body and so must be present
in our dietary protein foods.
Dietary sources of proteins
Animal proteins: lean meat, fish, eggs, milk and
cheese.
Plant proteins: beans and cereals.
SUF/BIO/MSPSBS/2012 4 OF 15
Dietary importance of proteins
For synthesis of new protoplasm, i.e. for growth and
repair of worn-out body parts e.g. hair, nails, red
blood cells, muscles, ligaments, tendons.
As a source of energy (1g yields 17kJ of energy);
only used when carbohydrates (glucose or glycogen)
and fats are all used up e.g. during starvation.
For synthesis of enzymes, hormones, antibodies,
haemoglobin, etc.
Note: Lack of proteins in daily diet will result in a
deficiency disease known as Kwashiorkor.
Kwashiorkor sufferers show signs of thinning hair,
edema, inadequate growth, and weight loss.
FOOD TEST
1. Test samples can either be a:
o Solid sample; the sample must be crushed and a
solvent (water or alcohol) will be used to
extract out the molecules.
o Liquid sample; unless stated, the volume of test
sample used would be 2cm3.
2. Keep the foods completely separate from each
other. Always use clean test-tubes, spatulas, white
tiles, Petri dishes and knives for each kind of food
to avoid contamination.
3. Use the same amount of reagent for each test.
(A) Test for simple sugars or reducing sugars.
Reducing sugars (glucose, fructose, galactose,
maltose and lactose) react with copper(II) ions in
Benedict’s solution and causes these ions to be
reduced to copper(I) ions which is red and insoluble.
This is the only food test which requires heating.
If the sample given is a solid, then begin with:
1. Crush the solid food specimen on a white tile
provided.
2. Place some crushed specimen in a test tube.
3. Add 2cm3 water (optional) and shake thoroughly
to mix the sample.
4. Add 2cm3 Benedict’s solution. Shake well.
5. Heat the mixture in a hot boiling water bath for
5 minutes.
If the sample given is a liquid:
1. Add equal volume of Benedict’s solution to the
liquid food specimen in a test-tube (2cm3).
2. Shake the mixture and heat it in a hot water
bath for 5 minutes.
Depending on the concentration of reducing sugar
present, the possible colour changes are from blue
to green to yellow to orange to red precipitate:
Green colour: very low concentration of
reducing sugar present.
Yellow colour: low concentration of reducing
sugar present.
Orange colour: high concentration of reducing
sugar present.
Red colour: very high concentration of reducing
sugar present.
Blue colour remains: reducing sugar absent.
(B) Test for starch
If the sample given is a solid:
1. Cut and crush the solid food specimen on a
clean glazed white tile.
2. Place some specimen in a clean test tube.
3. Add 2cm3 water to dissolve it (optional).
4. Add 1cm3 iodine solution. Shake well. Iodine
solution is 1% iodine in potassium iodide
solution. Iodine solution is brown in colour.
If the sample given in a liquid form:
1. Place 2cm3 of the specimen into a test-tube.
2. Add 1cm3 iodine solution. Shake well.
If the colour of iodine changes from brown to blue-
black, starch is present.
If the colour remains brown, starch is absent.
(C) Test for fats – The Ethanol Emulsion test
Fats will dissolve in alcohol but not in water.
If the sample given is a solid:
1. Cut and crush the solid food specimen on a
clean DRY glazed white tile. Place some crushed
specimen in a clean dry test-tube. DO NOT ADD
WATER!
2. Add 2cm3 of 100% ethanol.
3. Shake well and leave to stand for a few
minutes.
If the sample given is in a liquid form:
1. Place 2cm3 of the specimen into a clean DRY
test-tube.
2. Add 2cm3 of 100% ethanol.
3. Shake well and leave to stand for a few
minutes.
After step 3 for both samples either:
1. Decant the top portion of the liquid into another
clean test-tube containing 2cm3 of water; OR
2. Add water drop by drop to the mixture in the
test-tube.
Observation:
If a cloudy white emulsion is formed followed
with an increase in temperature, fat is present.
If a cloudy white emulsion is not formed, fat is
absent.
SUF/BIO/MSPSBS/2012 5 OF 15
(C) Test for proteins – Biuret Test
If the sample given is a solid:
1. Cut and crush the solid food specimen on a
clean glazed white tile.
2. Place some crushed specimen in a clean test
tube.
3. Add 2cm3 water (option). Shake well.
4. Add 2cm3 of Biuret reagent. If Biuret reagent is
not available or provided, add 1 cm3 of sodium
or potassium hydroxide followed by 1% copper
sulphate solution, drop by drop, shaking after
every drop.
If the sample given is a liquid:
1. Place 2cm3 of the liquid sample into a clean
test-tube.
2. Add 2cm3 of Biuret reagent. If Biuret reagent is
not available or provided, add 1 cm3 of sodium
or potassium hydroxide followed by 1% copper
sulphate solution, drop by drop, shaking after
every drop.
Observation:
If the colour changes from blue to purple,
protein.
If the colour remains blue, protein is absent.
MINERALS
Minerals are inorganic substances required only in
small amounts in the daily diet.
Calcium Iron
Sourc
es Flour
Milk
Cheese
Liver
Red-meat
Spinach
Functi
ons
For healthy bones and teeth (combines with phosphates to form calcium phosphates, one of the main components of teeth and bones)
For muscular contraction
For blood clotting
For formation of haemoglobin, oxygen carrying pigments in red blood cells
Defi
cie
ncy d
isease
and
sym
pto
ms
Rickets. Osteoporosis (porous bones);
Brittle bones which fractures easily.
Stunted growth.
Muscle spasm.
Dental decay.
Anaemia;
Dizziness.
Pale appearance.
Breathlessness.
Easily fatigued and weak.
VITAMINS
Vitamins are organic substances required only in
small amounts in the daily diet. They are needed for
normal health and development.
There are two types of vitamins, water soluble
(Vitamins B and C) and fat soluble (Vitamins A, D,
E and K) vitamins.
Water soluble vitamins cannot be stored in the body
and are removed from the body in the urine.
Therefore, they have to be supplied from the daily
diet.
Fat soluble vitamins can be stored in the body i.e.
in the body fats e.g. liver and adipose tissue.
Therefore, these do not have to be consumed daily.
Vitamin C
(Ascorbic acid) Vitamin D
(Calciferol)
Sourc
es
Citrus fruits (fresh)
Raw vegetables (fresh)
Fish liver
Egg yolk
Dairy products
The action of sun on the skin
Import
ance
For healthy gums
For aiding absorption of iron in the small intestine
For healthy capillaries and epithelial tissues
For skin repair especially in healing of wound
For aiding absorption of calcium in the small intestine
For formation of strong teeth and bones
Defi
cie
ncy
Scurvy: swollen bleeding gums, loosening of the teeth, painful swelling of joints, internal bleeding of muscles and skin.
Rickets: soft weak bones that bend and break under pressure, poor teeth and bone formation, bowed legs and knock-knees develop.
DIETARY FIBRE (ROUGHAGE)
Dietary fibre is indigestible cellulose cell walls of
plants.
Humans cannot digest cellulose or lignin due to the
absence of the enzyme cellulase.
Dietary sources of roughage
Fruits and vegetables.
Outer husks of cereal grains (bran) such as oats,
wheat and barley.
Whole meal bread, brown or unpolished rice.
SUF/BIO/MSPSBS/2012 6 OF 15
Dietary importance of roughage
Prevents constipation:
Provides bulk to feaces in the large
intestine/colon aiding the process of peristalsis.
Acts as a sponge to absorb water softening the
feaces.
Reduces the amount of fat absorption.
Reduces the risk of colon cancer.
WATER
In mammals, about 70% of the body weight is water
and in most conditions, humans can survive longer
without food than without water.
Dietary importance of water
Water is the medium or substance in which chemical
reactions occur in an organism such as hydrolysis
(breakdown of large, complex food molecules into
smaller simpler molecules).
Water helps to transport dissolved substances
around the body, such as:
digested products from the small intestine to
other parts of the body;
excretory products or waste products from the
tissue cells to the excretory organs for removal
from the body and
hormones from the glands to parts of the body
which require them.
Water is a key component of:
protoplasm;
lubricants found in joints;
the digestive juices;
blood and
tissue fluid.
Water helps to control the body temperature.
Water is a component of sweat and the evaporation
of sweat removes excess sweat from the body
preventing the body from overheating.
DIET
The food an animal eats everyday is called its diet.
A balanced diet is a diet that contains adequate
amounts of all the necessary nutrients required for
healthy growth and activity.
The body needs sufficient energy to maintain the
basal metabolic rate (BMR) and to sustain additional
activities of the individual.
Basal metabolic rate (BMR) is defined as the energy
needed for vital body functions (such as heartbeat,
circulation, brain function and essential chemical
reactions in liver and other organs) to keep alive
when the body is at rest.
The basal metabolic rate depends on the life-style,
climate, occupation, body size, gender, activities
and age; therefore, a balanced diet for one person
may not be balanced for another.
Climate
A person living in a cold country tends to lose more
heat to the surrounding and will require more food
to keep warm. This person will therefore have a
higher basal metabolic rate than a person living in
the tropics.
Body size
A person with a bigger build will require more
energy for their basal metabolism than a person
with a smaller build.
Age
Growing children has a higher basal metabolic rate
than adults as they need more energy for growth.
A child requires extra amounts of carbohydrates,
proteins and calcium in his/her balanced diet:
Carbohydrates: for energy.
Proteins: for growth.
Calcium: for formation of healthy bones and
teeth.
Gender
The basal metabolic rate for males is higher than
that of females. This is because women usually
have a greater amount of fatty tissue in their
bodies. This causes women to be more efficient in
preventing heat loss.
A menstruating female requires extra iron in her
balanced diet. Iron is important for the formation
of extra red blood cells to replace those lost during
menstruation.
A pregnant women requires extra amounts of
proteins, iron and calcium in her balanced diet:
Proteins: for healthy growth of embryo into
foetus (formation of new cells).
Iron: for formation of extra red blood cells to
accommodate foetal requirement for oxygen.
Calcium (+phosphate): for formation of foetus’s
bones.
Vitamins: for healthy development.
A lactating mother requires more intakes of
proteins, vitamins and calcium to produce milk of
adequate quality and quantity.
SUF/BIO/MSPSBS/2012 7 OF 15
Activities
An active adult or individuals who have an
occupation that involves heavy work will need more
energy than a person who is moderately active.
These active adults and manual workers need extra
amounts of carbohydrates, fats, proteins and water
in their balanced diet.
PROBLEMS CAUSED BY UNBALANCED DIET - MALNUTRITION
Malnutrition is the result of unbalanced diet of
either lack of food (undernutrition) or excess of
food (overnutrition).
Undernutrition
This is a lack of one or all types of food.
Starvation is the massive lack of all kinds of
food. It restricts growth, development of
muscles and deficiency diseases which
eventually causes death.
Famine is the lack of adequate amount of food
to support the population.
Starvation and famine may result from one or many
of the following factors:
Unequal distribution of food
The world produces enough food to sustain the
current population. However, some areas
overproduce while others do not produce enough.
Poverty
The cost of transporting food to where it is required
is often too high to those who need it, as they tend
to be those in the poor regions of the world.
Overpopulation
Some regions have more population than what their
food can adequately support. This may be
controlled through education and availability of
birth control methods. Some countries even
imposed laws to control population growth, such as
restricting the number of children per family.
Natural disasters
Quantity of products from farming can be severely
reduced by natural events such as flooding and
draughts. Sudan, Ethiopia and Chad have been
experiencing decreased rainfall for the last 200
years.
Crop failure due to diseases
Biological research is developing disease-resistant
crops and improved methods of disease control.
Poor farming techniques
Education on improved farming practices and
understanding on the effects of deforestation and
land clearing may ease the problems.
War or political instability
War or political instability within a region affects
the distribution of food in that region, where some
parts may not receive any food at all for long period
of time.
Overnutrition
This is the excessive intake of energy food everyday,
more than what the body requires. Excess energy
food will be stored up as either glycogen in the liver
or as fats in the body. This often leads to obesity.
Obesity means being very, very fat. It is a condition
that is very dangerous to health.
Physiologically, obesity has been related to many
other health problems such as hypertension,
diabetes and coronary heart disease.
Psychologically, it causes emotional stress and the
feeling of being socially rejected as a result of poor
self image.
Cardiovascular disease
The excess weight stresses the joints and also puts
extra strain on the heart as it has to work extra
hard to pump blood to the skeletal muscles.
The excess animal fats and cholesterol in blood
forms deposits called atheroma on the walls of
arteries. This causes the walls to harden.
Atheroma decreases the diameter of the lumen of
the arteries (atherosclerosis).
Both the extra volume of blood as well as the
formation of atheroma results in hypertension,
which increases the risk of heart disease.
If atheroma occurs on the walls of the coronary
artery (the blood vessel that carries blood to the
cardiac muscles of the heart), it will restrict the
blood flow to the heart muscles, decreasing their
oxygen supply.
In severe cases, the artery may become blocked
either by the atheroma itself or by a blood clot,
leading to cardiac arrest (heart attack). If this
occurs in the brain, this may lead to stroke.
SUF/BIO/MSPSBS/2012 8 OF 15
NUTRITION
The intake of food, with the changes that result in
the conversion of food substances into living matter,
is known as nutrition.
Nutrition may be divided into two types:
1. Autotrophic Nutrition.
2. Heterotrophic Nutrition.
Plants feed by autotrophic nutrition. “Auto” means
self and “trophic” means feeding. So autotrophic
nutrition means that plants feed itself and does not
rely on other living things to make its food for it.
Animals cannot make their own food. They feed on
organic substances which have been originally made
by plants. This is called heterotrophic nutrition.
“Hetero” means other and so heterotrophic
nutrition means that an animal feeds on substances
made by other organisms.
Heterotrophic nutrition in animals
Human (heterotrophic) nutrition involves five basic
stages:
(1) Ingestion (eating/feeding)
Taking food into the alimentary canal via mouth.
(2) Digestion
Mechanical digestion: Chopping and grinding of
food (with teeth) and muscular churning of food (in
the stomach).
Chemical digestion: Breaking large, insoluble
molecules into small soluble ones via the action of
enzymes in the alimentary canal (in the presence of
water = hydrolysis)
(3) Absorption
Transport of soluble food products into the
bloodstream via villi in the ileum.
(4) Assimilation
Using the absorbed food in the metabolic processes
and conversion into new protoplasm.
(5) Egestion / Defecation
Removal of any undigested and unabsorbed food
from the alimentary canal via anus.
The need for chemical digestion
Most foods contain insoluble starch, proteins and
fats, as these are large and complex molecules.
These large insoluble molecules cannot be absorbed
into the bloodstream so they need to be broken
down into small, soluble and absorbable / diffusible
ones.
Glucose, amino acids, fatty acids and glycerol are
the smallest forms of their ‘parent’ molecules.
HUMAN DENTITION
The function of teeth is to chew food and cut it into
tiny pieces.
Chewing increases the surface area of food and
helps to speed up the action of digestive enzymes
allowing digestion to be more rapid and efficient.
It also helps to dissolve the soluble parts of the
food.
Chewing is only a mechanical digestion of food
where the food remains chemically unchanged.
SUF/BIO/MSPSBS/2012 9 OF 15
Types of teeth, dentition, tooth structure and function
Every human being has two sets of teeth in his life-
time.
The first set of teeth is called milk teeth or
deciduous teeth. Later this milk set is replaced by
a permanent set of 32 teeth.
If the permanent teeth are lost any reason, they will
not grow again.
The number, the type and the arrangement of the
teeth in a mammal is called dentition. This can be
expressed using the dental formula.
In the dental formula, the letters express the
different types of teeth in one half of the upper
and lower jaws, and the numbers expresses the
number of each type of teeth.
Dental formula of milk teeth:
i 2
2 : c
1
1 : pm
0
0 : m
2
2
Dental formula of permanent teeth:
i 2
2 : c
1
1 : pm
2
2 : m
3
3
There are four different types of human teeth:
Types of teeth Function
Incisors
Sharp-edge, chisel-shaped teeth at the front jaw.
Single-rooted.
2 in each quarter jaw (milk and permanent dentition).
For biting and cutting food.
Canines
Sharp, cone-shaped and pointed.
Single-rooted.
1 in each quarter jaw (milk and permanent dentition).
For biting and tearing food.
Premolars
Surface of each tooth have two projections or cusps.
Single-rooted.
2 in each quarter jaw (permanent dentition only).
For cutting, crushing and grinding food.
Molars
Tooth surface is square with 4 cusps.
Double-rooted.
3 in each quarter jaw (milk and permanent dentition).
For crushing and grinding food.
SUF/BIO/MSPSBS/2012 10 OF 15
Parts of a tooth
Composition Function(s)
Enamel Hard, non-living layer of calcium salts.
Forms a hard, biting surface; Protects dentine.
Dentine Softer, bone-like layer.
Acts as a shock absorber.
Pulp cavity
Contains blood capillaries; Tooth cells and nerves present.
Supply food and oxygen to cells; Tooth cells divide to form dentine.
Cement A thin layer of bone-like material
Covers dentine of root and holds root in socket in jaw
Fibres Embedded in the cement.
Allow slight movement of root in socket.
Jawbone and
socket
Bone structure made of calcium phosphate.
Tooth fits into sockets of jawbone.
Root opening
Entrance for blood capillaries and nerves
For blood supply, growth and replacement of tooth; Nerves carry messages to and from brain.
DENTAL DECAY
If teeth are not properly cared for, they may suffer
from dental caries or decay.
The process of dental decay:
1. Small amounts of food, particularly those rich in
sugar, are left on and between the teeth.
2. There are large numbers of harmless bacteria
living in the mouth. Some of these bacteria
stick to the surfaces of the teeth forming a thin
film called dental plaque.
3. Bacteria feed on the sugary deposits using them
for their own metabolism and grow within the
plaque.
4. Bacteria secrete acids as a result of their
metabolism. These acids dissolve the outer non-
living enamel covering of the tooth.
5. A cavity develops, in which more sugary deposits
collect. More bacteria settle secreting more acids.
The size of the cavity increases.
6. Eventually, the cavity reaches the living parts of
the tooth. The first part affected is the dentine,
where there are nerve endings causing toothache.
Then the decay reaches the pulp cavity leading to
an abscess i.e. painful swelling of the gums filled
with puss.
Oral hygiene
Do not eat sweet or starchy foods before going to
bed.
Reduce daily intake of sugary food.
Ensure daily diet contains sufficient calcium,
phosphorus and Vitamin D for the formation and
maintenance of strong teeth.
Brush teeth regularly particularly after eating, first
thing in the morning and before going to sleep.
Use dental floss regularly to remove fragments of
food from between the teeth.
Use a toothpaste which contains:
Fluoride: to strengthen tooth enamel.
Bacteriacide / Antiseptic: to kill bacteria.
Alkaline: to neutralise acids released by the
bacteria
Visit a dentist regularly for an examination and have
treatment if required.
DIGESTIVE SYSTEM: HUMAN ALIMENTARY CANAL
SUF/BIO/MSPSBS/2012 11 OF 15
The alimentary canal consists of the following parts:
The whole of the alimentary canal consists of layers
of muscles and cells which secrete a slimy liquid
called mucus.
The slimy mucus makes it easier for the food to
move along.
The layers of muscles bring about wave-like
contractions called peristalsis which push food
along the alimentary canal.
The Mouth
Food enters the body through the mouth, which
leads into the buccal cavity (pharynx).
In the mouth there are:
1. Teeth: Chewing action of the teeth
(mastication) breaks down large pieces of food
into smaller pieces. This increases the surface
area to volume ratio of the food so enzymes
can act it more efficiently.
2. Salivary glands: These three pairs of glands
which produce saliva; a slightly alkaline
digestive juice, contain an enzyme called
salivary amylase (ptyalin) which digests starch.
3. Tongue: It mixes the food with saliva and then
rolls it into small, slippery balls called bolus
(plural: boli). These balls of food are then
swallowed. Mucin, which is present in the
saliva helps to soften food pass it smoothly from
the mouth to the oesophagus.
The Oesophagus
The oesophagus or gullet is a narrow, muscular tube
leading from the mouth to the stomach.
The wall of the oesophagus is made up of two layers
of muscles. These muscles are present along the
gut from the oesophagus to the rectum.
The two layers of muscles are:
1. Longitudinal muscles on the outside of the gut.
2. Circular muscles on the inside of the gut.
These two muscles are called antagonistic muscles
which means that if one muscle contracts the other
relaxes. The movement of these two muscles
produces long, slow contractions which move food
along the gut.
During peristalsis:
Behind the food bolus: Circular muscle contracts
(small lumen), longitudinal muscle relaxes.
Aim: To decrease the diameter of the lumen
pushing the food bolus forward.
Region of food bolus: Circular muscle relaxes
(wide lumen), longitudinal muscle contracts
(shorter distance).
Aim: To allow the lumen to widen to
accommodate the food bolus, and to shorten
the distance across which the food bolus has to
move.
For smooth movement of food throughout the
alimentary canal, the food passage is lubricated
with mucus (to reduce friction).
The Stomach
The stomach is a distensible (can be stretched or
expanded) muscular bag, with thick and well-
developed muscular walls.
When the stomach is fully distended, it sends signals
to the brain that it is full or sated.
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The stomach has two rings of muscles called
sphincters, one at its entrance and one at its exit.
These sphincters control food going into and out of
the stomach.
Gastric glands in the wall of the stomach secrete an
acidic digestive juice called gastric juice. Gastric
juice is a dilute solution of hydrochloric acid (about
pH 2) and two enzymes, pepsin and rennin.
The dilute hydrochloric acid:
Stops the action of salivary amylase by
denaturing it.
Provides an optimum pH for pepsin and
rennin. Pepsin belongs to a type of enzyme
known as protease which digest proteins by
breaking them into amino acids.
Rennin curdles or coagulates milk by changing
soluble caseinogens to insoluble casein.
Kills certain potentially harmful
microorganisms in food.
Food normally remains in the stomach for about
three to four hours. The partly digested food
becomes liquefied, forming chyme.
Chyme passes in small amounts into the duodenum
when the pyloric sphincter relaxes and opens.
The Small Intestines
The small intestine is a long narrow tube of about 5
– 6.4 metres long in a normal adult human and is
divided into the duodenum and ileum.
The Duodenum
The duodenum is the first part of the small
intestine.
It is a U-shaped tube of about 30 cm long.
It receives three types of digestive juices:
1. Bile juice from gall bladder in the liver.
Liver is the largest internal organ and it
produces bile; a green-yellow coloured
fluid, which is stored temporarily in the gall
bladder. Bile is transported into the
duodenum via the bile duct.
Bile is the product of breakdown of old red
blood cells in the liver. Bile juice contains:
a) Bile salts: emulsifies fats i.e. converts
large fat droplets into small droplets.
Emulsification increases the surface
area for the enzyme lipase to act on
therefore, faster enzyme action.
b) Bile pigments: gives the colour of bile
juice, removed with faeces (gives colour
to faeces)
Bile juice has an alkaline pH and is
important for neutralising the acidic chyme
from the stomach.
2. Pancreatic juice from the pancreas.
Pancreas lies between the stomach and the
duodenum.
Pancreatic juice contains:
1. Lipase: digests fats into fatty acids and
glycerol.
2. Amylase: digests any remaining starch
into maltose.
3. Trypsin: digests proteins into
polypeptides.
4. Sodium Hydrogen Carbonate (NaHCO3):
To provide a slightly alkaline pH for
the enzymes to work in.
To neutralise the acidic chyme from
the stomach.
The pancreas is also an endocrine gland
where it produces the hormones insulin and
glucagon for controlling the concentration
of glucose in the blood and carbohydrate
metabolism.
3. Intestinal juice produced by duodenal walls.
The juice contains:
1. Lipase: digests fats into fatty acids and
glycerol.
2. Erepsin: digests polypeptides into amino
acids.
3. Maltase: digests maltose into glucose.
4. Sucrase / Invertase: digests sucrose into
glucose and fructose.
5. Lactase: digests lactose into glucose and
galactose (This enzyme is absent in lactose
intolerant individuals)
SUF/BIO/MSPSBS/2012 13 OF 15
SUMMARY OF DIGESTION
REGION OF DIGESTION
SECRETION SOURCE ENZYME ACTION
MOUTH Saliva Salivary Glands
Salivary Amylase
Starch maltose
STOMACH Gastric juice
Gastric glands
Pepsin Proteins polypeptides
Rennin Soluble caseinogens insoluble casein
DUODENUM
Bile Liver - Bile salts emulsify fats.
Pancreatic juice
Pancreas
Amylase Starch maltose
Trypsin Proteins polypeptides
Lipase Fats fatty acids and glycerol
Intestinal juice
Intestinal glands
Sucrase Sucrose glucose + fructose
Maltase Maltose glucose
Erepsin Polypeptides amino acids
Lactase Lactose glucose + galactose
Lipase Fats fatty acids and glycerol
OPTIMUM pH
pH 2.0 pH 6.5 – 6.8 pH 8.5
Pepsin and Rennin Salivary Amylase
or Ptyalin Trypsin and other intestinal juice
END PRODUCTS OF DIGESTION
SUBSTRATE END PRODUCTS
Carbohydrates Glucose, Fructose and
Galactose
Proteins Amino acids
Fats Fatty acids and glycerol
ABSORPTION
Products of digestion such as simple sugars, amino
acids, fatty acids and glycerol are absorbed
throughout the small intestines especially the ileum.
The absorbed nutrients pass from the small intestine
into the blood stream.
Ileum
The ileum is the last part of
the small intestine. This is the
region where absorption of
digested food takes place.
The structure of the ileum is
highly adapted in order to
carry out its function. The
main aim of the adaptations is
to increase the surface area
for absorption as much as
possible.
THE PROCESS OF ABSORPTION
Simple sugars and amino acids
diffuse through the walls of
the villi into the blood
capillaries.
They can also be absorbed by
active transport against the
concentration gradient in
times of starvation, diets,
anorexia, etc.
The blood capillaries are
connected to the hepatic
portal vein where they are
transported to the liver.
Minerals salts and vitamins
also diffuse into the blood
capillaries of the villi.
Glycerol is soluble in water
and it diffuses into the
epithelium.
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Fatty acids react with bile salts to form soluble
soaps, and then diffuse into the epithelium.
In the epithelium, the soaps and glycerol recombine
to form minute fat globules, which are absorbed by
the lacteals.
FEATURE OF SMALL INTESTINE (ILEUM)
HOW THIS HELPS ABSORPTION TO TAKE PLACE
1. It is very long, about 6m in adult.
This gives plenty time for digestion to be completed, and for digested food to be absorbed as it passes through.
2. It has villi. Each villus is covered with cells which have even smaller projections on them called microvilli.
This increases the surface area of the small intestine for rapid and efficient absorption of digested food.
3. Villi contain blood capillaries.
Digested food diffuse into the blood and is transported to the liver by the hepatic portal vein.
4. Villi contain lacteals, which are part of the lymphatic system.
Fats are absorbed into the lacteals.
5. Villi have walls only one cell thick.
The digested food can easily cross the wall to reach the blood capillaries and lacteals.
The large intestine (Colon), Rectum and Anus
The large intestine or colon is about 1.5m long.
The colon absorbs excess water, salts and vitamins.
For more effective absorption, its walls are folded
transversely to increase its surface area.
The indigestible fibre provides the faeces bulk
against which the muscles of the colon can push.
The large intestine also secretes mucus, which acts
as a lubricant to facilitate the peristalsis of faeces
through the rectum and anus.
The rectum is a muscular storage chamber where
undigested food (faeces) is held temporarily and
moulded before being pushed out through the anus
during egestion.
The anus is the exit to the alimentary canal. It is
closed by a ring of muscle called the anal sphincter
which is relaxed during egestion.
ASSIMILATION
After the digested food has diffused into the blood
capillaries of the villi, the food is taken to the liver
via the hepatic portal vein. Here, the small food
substances, absorbed as small soluble molecules,
must now be built up into the larger molecules
needed by the body.
Sugars
Glucose and any other simple sugars absorbed by
the villi may be used as it is; as a substrate for
respiration to release energy.
However, after a meal, there is more glucose
available than is needed immediately and so, these
excess glucose molecules need to stored.
Insulin, a hormone secreted by the pancreas,
regulates blood glucose concentration.
Insulin converts glucose into large insoluble
molecule, glycogen, which is stored in the liver and
muscles.
Glycogen can be converted back into glucose when
there is insufficient glucose supply in the diet, using
the hormone glucagon (also from pancreas).
Amino acids
Amino acids are transported around the body for
growth and repair of worn out cells.
They are also used for the formation of enzymes and
hormones.
Any excess amino acids are broken down in the liver
by a process called deamination.
This is the removal of their amino group (-NH3)
leaving a carbohydrate backbone.
Two separate molecules are produced as a result of
deamination:
1. A carbohydrate which can be changed into
glucose. Excess glucose will be converted into
glycogen and stored.
2. Urea, a nitrogenous waste product which passes
in the blood from the liver to the kidneys for
excretion in urine.
Fats
Once in the blood, fatty acids and glycerol
recombine to form tiny fat droplets.
Lipids are stored in special storage cells in the skin
known as adipose tissue and around the body
organs such as the kidneys.
SUF/BIO/MSPSBS/2012 15 OF 15
Other functions of the liver
The liver is the largest gland in the body and weighs
about 2kg.
It is situated just below the abdomen.
It is dark red in colour because it contains a lot of
blood.
Apart from the production of bile, the regulation
of blood glucose and the deamination of amino
acids, other functions of the liver include:
1. Iron storage: vitamin B12 is necessary for the
maturation of red-blood cells and this is stored
in the liver until required. The liver also stores
iron for the manufacture of haemoglobin.
2. Detoxification: the removal and breakdown of
poisons (toxins) from the blood such as alcohol.
Liver can remove small quantities of alcohol on
a regular basis. However, high levels of alcohol
in the blood can eventually lead to liver disease
or ‘cirrhosis’.
3. Heat production: heat is formed as a result of
numerous chemical activities occurring in the
liver and is distributed by the blood to other
parts of the body, thus helping to maintain the
body temperature.
4. Prothrombin and fibrinogen production: these
two substances are essential for the clotting of
blood and are formed in the liver.
5. Fat metabolism: fat is mainly stored in the
saturated form. When it is required by the
tissues to provide energy, the liver performs a
chemical change by removing the hydrogen and
converting the fat into the unsaturated form for
use.
6. Storage of vitamins: the liver stores vitamin A
and D.