form 5 biology chapter 1 transport (c).docx

Form 5 Biology Chapter 1 Transport (c)

Role of the Circulatory System in the Body’s Defense Mechanism

First Line of Defence

1. First line of defence mechanism is nonspecific and immediate

2. The first line of defence consists of physical and chemical barriers that prevent

pathogens from entering the body

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Physical Barrier

The outer layer of skin is tough and it is a barrier that is impermeable to

bacterial and viruses. The continual shedding of dead skin cells makes

bacteria difficult to grow on skin. When the skin is cut, blood clots to seal the

wound and prevent the entry of microorganisms.

Coughing and sneezing also help to expel microorganisms and dirt from the

respiratory tract.

Cilia in the trachea and bronchi, the rhythmic movement of cilia carries the

mucus towards the throat where it is swallowed or spit out.

The mucous membranes - The layers of cells that line the trachea respiratory,

digestive and urogenital tracts. It secrete sticky fluid, mucus, that contains

lysozymes which trap and destroy microorganisms.

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Chemical Barrier

Lysozyme is also present in the saliva from the salivary glands and other nasal

secretions

Hydrochloric acid in the stomach kills microorganisms present in the food and

water.

Perspiration excreted from the sweat glands contains lysozyme and acids which

destroy harmful bacteria and inhibit the growth of fungi on the surface of the

skin.

Tears secreted by the tear glands contain lysozyme and acids to protect the

surfaces of the eyes from infection of bacteria and to prevent the entry of foreign

substances.

Mucus is secreted by the cells of mucous membranes to trap microorganism

Sebum secreted by the skin has a low pH value to prevent the growth of some

bacteria and fungi

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Second Line of Defense

1. The second line of defense comes into play when the pathogens succeed in

penetrating the skin or the mucous membrane.

2. The nonspecific immune responses include:

a. Phagocytosis carried out by the white blood cells such as neutrophils,

macrophages and eosinophils.

b. natural cell killers destroy infected cells and precancerous cells

c. inflammation which involves redness, heat, swelling and pain.

d. Fever (high temperature) stimulates phagocytosis, kills certain bacteria by

denaturing their protein and helps in the healing process.

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Phagocytosis

1. Phagocytosis is a process of encirclement and digestion of microorganisms or

foregin particles by the phagocytes.

2. Two common types of phagocytes are the neutrophils and macrophage

3. The following are some explanation about neutrophils

a) They circulate freely through the blood vessels to engulf and destroy any

pathogen.

b) The can squeeze between the cells of the walls of the capillaries to reach

the site of infection

c) They are the first phagocytes to arrive at the injured tissue before the

arrival of macrophages.

4. The information below are about macrophages

a) Two or more monocytes can develop into macrophages

b) They engulf and digest any bacteria, viruses and foreign particles

c) They remain in a body tissue, wait for pathogen or move around seeking

out pathogens.

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Third Line of Defence7


Immunity, Antigens and Antibodies

1. The third line of defence takes over if a pathogen gets past the first and second

lines of nonspecific defences.

2. The third line of defence:

a. depends on the ability of the body to resist a particular disease by recognising

and defending itself against the specific pathogens or antigens

b. involves the immune response

3. Immunity is the ability of the human body to resist infection.

4. An immune response refers to the body’s defence reaction whereby an antigen

(e.g. bacterium) is recognised and specific antibodies are produced by

lymphocytes to defend against the pathogen.

5. In fighting against specific antigens, apart from the production of antibodies,

specialized lymphocytes are also involved.

6. Antigen:

a. An antigen (antibody generator) is a foreign protein molecule that when

introduced into the body, stimulates the production of antiobodies.

b. Antigens include molecules belonging to viruses, bacteria, fungi, protozoan

parasitic worms, and non-pathogens like pollen and transplanted tissue.

c. Antigens from pathogens are toxic and can cause harm to the human body.

7. Antibody:

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a. An antibody is protein substance produced by the immune system in response

to the recognition of a specific antigen.

b. An antibody is a large Y-shaped protein molecule, which is also known as an

immunoglobulin.

c. An antibody is produced by the immune system to destroy or to weaken a

pathogen and neutralises its toxin, which forms the basis of the immune

response.

Ways Which Antibodies Help to Defend the Body

1. The antibodies produced defend the body through these following ways:

(a)Agglutination (b) Opsonisation

(c)Neutralisation (d) Lysis

2. Agglutination of microorganisms:

(a)Antibodies bind to the antigens and clump microorganisms together in

large numbers, making the antigens harmless.

(b)These incapacitated pathogens are then ingested by the phagocytes.

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3. Opsonisation:

(a)Some pathogens or antigens are not recognized by the phagocytes and do

not resemble the body’s protein.

(b) Antibodies bind to the antigens and cover them, making it easier for the

phagocytes to eat them.

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4. Neutralisation:

(a)Antibodies bind to the toxins (antigens), thereby neutralising the poison

simply by disabling the chemical action of the toxins.

(b) When an antibody binds to a toxin, it is called an antitoxin (if the

toxin comes from some form of venom, it is called an antivenin).

(c)The disabled toxin is then ingested by the phagocytes (macrophage).

5. Lysis

Antibodies bind to the pathogen and the plasma membrane of the pathogen

disintegrates

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[SBP 2014]

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Activation of Lymphocyte (not important but crucial to understand active

immunity later)

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Type of Immunity

Type of immunity Characteristics Examples

Active immunity

a) Natural acquired active immunity or immunity that is obtained after a person recovers from an infection

When a person is exposed to a pathogen, the antigens of the pathogens stimulate an immune response.

The immune system produces antibodies in response to the antigens

After the person recovers from the infection, the person is immune to the pathogen because the

The person is immune to the chickenpox virus after he has been infected by it.

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lymphocytes remain in the body.Permanent immunity follows the infection.

b) Artificially acquired active immunity or immunity that is obtained through immunization or vaccination

Some diseases such as measles are highly contagious.

A serious illness or death may result when a person is exposed to the pathogens for the first time.

Therefore, a person needs to be immunized, that is, to activate his immune response artificially by injecting a vaccine before the infection occurs.

A vaccine is a preparation of weakened, dead or non-virulent forms of a pathogen that is not harmful to the person who receives it.

The process of inducing immunity by administering a vaccine is called immunization.

The vaccine that contains weakened live microorganisms causes only very mild symptoms. The vaccine containing killed viruses or bacteria can stimulate an immune response but cannot induce the disease.

Therefore, the body has acquired immunity through vaccination.

Subsequently, if a live pathogen invades the body, it is able to eliminate the pathogen

The person becomes immune to the measles virus after being inoculated with the measles vaccine.

Other examples are vaccination against hepatitis B, diphtheria, pertussis, tetanus, and poliomyelitis.

Examples of vaccines are the Salk poliomyelitis vaccine and the Sabin vaccine.

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immediately because it already has the antibodies against the pathogen.

Passive immunity

a) Naturally acquired passive immunity or immunity that is obtained from the mother either through the breast milk or via the placenta

A foetus can receive maternal antibodies naturally from its mother through the placenta.

These antibodies prevent the baby from getting disease in the first few months after birth.

Babies can also acquire passive immunity through breastfeeding as the antibodies are found in the mother’s milk or colostrums.

Passive immunity is temporary because the antibodies are evenly broken down in the spleen and liver.

Antibodies that are transferred through the placenta or mother’s milk.

b) Artificially acquired passive immunity or immunity that is obtained through the injection of a serum which contains specific antibodies

An immunity that is obtained through the injection or transfusion of a serum containing a specific antibody against the disease.

For example, a serum which contains antibodies or an antiserum from donors can be injected into a person who needs the antibodies, for example, travelers visiting countries where hepatitis is endemic.

These antibodies temporarily protect the travelers in the event they are exposed to the hepatitis virus.

A serum containing specific antibodies against specific diseases such as tetanus and rabies or for venom of snake bites.

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This type of immunity, although effective, usually disappears after several weeks or months.

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Difference between active immunity and passive immunity

Artificially acquired active

immunity

Artificially acquired passive immunity

Injection of vaccine Injection of serum

Body produces its own antibodies Antibodies are obtained from outer source

Does not result in an immediate

immunity. It takes time to develop

Immunity is immediate

Vaccination is given before infection Injection of serum is given when infection

occur or has a high risk of getting the

disease

Formation of memory cells No memory cells formed

Immunity lasts very long Immunity lasts temporarily

Booster does is given to stimulate

more lymphocytes to produce more

antibodies

Second injection is given to boots

immunity if antigens are yet neutralized.

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Question 1: Sketch the graph of concentration of antibodies against time for

Artificially Acquired Passive Immunity and Artificially Acquired Active

Immunity.

Question 2: Why sometime second injection of vaccine is given?

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Question 3: Why a person who is bitten by poisonous snake cannot be given

vaccine to cure the poison?

Question 4: There is a mother who had recovered from chickenpox breastfeeds

her child. During this period, the baby receives the immunity from his mother

and there is no chance for the baby gets infected by chickenpox virus. However,

after the baby grows up he is still infected by chickenpox virus. Why?

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Question 5: Explain the series of inflammation response.

Vasodilation: leads to greater blood flow to the area of inflammation, resulting in redness and heat.

Vascular permeability: endothelial cells become "leaky" from either direct endothelial cell injury or via chemical mediators.

Exudation: fluid, proteins, red blood cells, and white blood cells escape from the intravascular space as a result of increased osmotic pressure extravascularly and increased hydrostatic pressure intravascularly

Vascular stasis: slowing of the blood in the bloodstream with vasodilation and fluid exudation to allow chemical mediators and inflammatory cells to collect and respond to the stimulus.

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[Perak 2011]

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[SBP 2014]

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[Terengganu 2013]

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AIDS (Acquired Immunodeficiency Syndrome)

1. Human immunodeficiency virus (HIV) is a virus that attacks the human immune

system.

2. Infection caused by the HIV leads to acquired immunodeficiency syndrome

(AIDS).

The effects of HIV on the body’s immune system

1. When a person has AIDS, the infected person is vulnerable to various infections

because his immune system cells are being destroyed progressively.

2. AIDS is the end stage of infection by the virus.

3. The virus reproduces inside the lymphocytes and destroys them in the process.

4. A person who is infected with HIV may be symptom-free for many years, even

when the virus is actively attacking his immune system.

5. The disease may take 8 to 10 years to develop and for the symptoms to manifest.

6. Since the immune system of a person is weakened, the body is vulnerable to

many types of infections.

7. Eventually, the immune system collapses and victim dies of an infection that his

immune system would have been able to cope with under normal circumstances.

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Transmission of HIV

1. HIV enters the body through the transfer of body fluids (for example, blood or

semen) or across the placenta.

2. Newborn babies can be infected with the virus from their infected mother at birth

or through breastfeeding. However, HIV infection of fetuses and newborn babies

can be prevented if the infected mothers get proper medical treatment during

pregnancy and delivery.

3. Teenagers and adults can get the disease from unprotected sex with an infected

person and contaminated needles used to inject drugs or for tattoos.

Prevention of AIDS

1. Blood products used should be treated to destroy the virus

2. Education programs should inform everyone about the risk of unprotected sex

and the sharing of needles.

3. Use condoms to reduce the risk of infection.

4. Stay away from sex with many partners. Partners in a new relationship should

check their HIV status by having a blood test.

5. To date, there is no vaccine yet for AIDS although certain drugs may retard the

progress of the disease.

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