Body's Defence Mechanismk

8/12/2019 Body's Defence Mechanismk

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1. Humans are constantly invaded bydisease-causing microorganisms or

pathogens.2. A healthy body is able to protect itself

from these pathogens.

3. Besides transport, the circulatory systemplays an important role to bodysdefence mechanism against diseases.

4. There are three lines of defencemechanism in the body.


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The first line of defencei.

The first line of defence is the bodysnatural barriers, including the skin andmucous membranes.

ii. The function of the first line of defence

is to prevent pathogens from enteringthe body.

iii. The skin is an effective barrier against

the entry of microorganisms because ofits tough outer layer of closely packeddead cell.


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The first line of defenceiv.

The mucous membrane consists of cells liningthe respiratory tract and openings of theurinary and reproductive systems. Themembrane secretes a protective layer ofmucus.

v. Mucus is sticky and traps pathogens and otherparticles. For example, dust andmicroorganisms breathed in through the noseare trapped in sticky mucus which covers themembranes lining the nasal cavity and

trachea. Trapped dust and microorganisms arethe carried by cilia to the esophagus, wherethey are swallowed and eventually passed outin the faeces.


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Process of phagocytosis

Stage 1 The phagocyte is attracted tochemicals produced by themicroorganism (bacterium).

Stage 2 The phagocyte sticks to themicroorganism.

Stage 3 The phagocyte extends itspseudopodia to engulf themicroorganism.

Stage 4 The phagocyte produces hydrolytic

enzymes to digest the microorganism.Stage 5 The products of digestion are absorbed

into the cytoplasm by the phagocyte.


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Process of phagocytosis


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The third line of defence

i. Lymphocytes in the blood producechemicals called antibodies that destroybacteria and viruses before they get

inside the body cells.

ii. Lymphocytes originate in the bonemarrow and migrate to the lymph nodes,

where they mature and continue tomultiply in larges numbers.


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Immunity, Antigen, Antibody and

Immunisation

Immunityis the ability of an organism toresist infection.

An antigenis a foreign substancecapable of stimulating an immuneresponse or for the formation ofantibodies. Examples of antigens are

pathogens, toxic substances, and variousharmless molecules and cells.


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Immunity, Antigen, Antibody and Immunisation

Antibodies are proteins that interact with the

antigens and thereby rendering them harmless.Antibodies are highly specific because each typeof antibody can interact with one specificantigen only.

Immunisationis a technique used to induceimmunity to a specific disease in humans or theanimals by exposing the individual to an antigenin order to stimulate the production of specificantibodies. Immunisation is achieved through

injecting a vaccine that contains killed orseverely weakened antigen into the body of anindividual.


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How do antigen and antibody relate to

immunity?

1. When an antigen enters the body, thelymphocyte produces a specific antibody tointeract with the antigen.

2. Antibodies vary in their effects on antigens.

a. Opsoninsare antibodies that bind toantigens on the outer surface of amicroorganism. This enables

phagocytes to recognise themicroorganism and destroy it.


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How do antigen and antibody relate to

immunity?

b. Agglutininsare antibodies that bindto antigens, causing the microorganismto clump together. In this state, themicroorganisms cannot enter the hostcells to reproduce.

c. Lysinsare antibodies that bind to theantigens of a microorganism causingthe microorganism to rupture ordisintegrate.

d. Antitoxinsare antibodies that bind tothe toxins produced by microorganismsrendering them harmless to the body.

3. Antibodies provide specific immunity to the body.


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Various types of immunity

Typerofimmunity

Active Passive

Natural Artificial Natural Artificial


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Active immunity

Occurs when an individuals own immunesystem produces its own antibodies todefend against specific antigens.


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Two types of active immunity.

Natural active immunity

a. It occurs after an individual has recoveredfrom certain diseases.

a. For these disease, such as mumps,measles and chicken pox.

Artificial active immunitya. It can be established upon immunisation orvaccination.

b. Vaccines consist of living but harmless(attenuated) pathogens, dead pathogens, ortoxic chemicals from pathogens which havebeen rendered harmless (toxoids)


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Two types of active immunity.

Artificial active immunity

a. It can be established upon immunisationor vaccination.b. Vaccines consist of living but harmless

(attenuated) pathogens, deadpathogens, or toxic chemicals frompathogens which have been renderedharmless (toxoids)

c. Vaccines are normally injected into the bodyto activate the lymphocytes which will be

well-pathogen gets into the body.d. Vaccines are available for diseases such as

rubella, mumps, measles and poliomyelitis.


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Graph showing antibody level in the blood of an individual

after vaccination


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Passive Immunity

Occurs when an individual is given theantibodies required to defend against thepathogen.


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Two types of passive immunity.

Natural passive immunity

a. It occurs when antibodies produced bythe mother are passed across theplacenta to the fetus during

development or in a early infancythrough breast milk.

b. The first formewd milk called coloctrum

is very rich in antibodies.


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Two types of passive immunity.

Artificial passive immunity

a. It is achieved when ready-madeantibody or antiserum is injected intothe individual.

b. Such antiserum is prepared from theblood of humans, cows or horses.

c. Antiserums are used to treat individuals

exposed to rabies, hepatitis, tetanusand snakebites.


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Differences between active immunity and passive

immunity

Active immunity Passive immunity

The body cells of anindividual produce theantibodies required todestroy the pathogen.

An individual is given theantibodies required todestroy the pathogen.

Can last for months or

years

Can only last for a short

period of about onemonth

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Body's Defence Mechanismk