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1.5: The role of circulatory system in the bodys defencesystem

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Bodys Defence Mechanism Circulatory System (CS) also defends the body against

disease abolition of the disease causingmicroorganisms (pathogen)

Humans have 3 lines of defence against pathogens:

FIRST LINE OFDEFENCE

THIRD LINE OFDEFENCE

Skin

# sweat# sebum

Phagocytosisby phagocytes

SECOND LINEOF DEFENCE

MucousMembranes#Secretion of

mucus

Antibodiesproducted bylymphocytes

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First line of defence

-prevent of pathogen entering the body

(i) Skin

-as a physical barrier

-is made up of a dead keratinised layer- tough enough for pathogen topenetrate

If there is a scratch/cut , the blood clotsto seal the wound & avoids infection

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-as a chemical barrier (a) sweat gland secretes sweatwhich contains salt ,

& lysozyme ( destroy bacteria)

(b) Sebaceous gland secretessebum-which contains acid &oil

## All these substances areunfavourable for growth of

microorganisms

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(ii) Tears & Saliva

-Contain lysozyme - protect theeyes & mouth from pathogeninvasion

(iii) Gastric juice in stomach

-contain hydrochloric acid destroys most pathogens in foods &drinks

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(iv) Mucous membranes

-secrete mucus in nasal cavity &tracheas to trap the dustparticles & spores

- The cilia in the respiratory tractsweep the trapping particles

to the pharynx & stimulatesneeze /cough to expel out the

pathogens

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Second line of defence (non-specificdefence)

-killing the pathogens that entered our body byaction ofphagocyticwhite blood cells(neutrophill & monocyte)

known as phagocytes(process: phagocytosis)

-occur when the pathogens get through the first

line of defence .-Phagocytes move to the infected area due to the

stimulation by chemicals released by damaged

cells example cut skin.

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The third line of defence (antibody)

1)is a kind ofprotein released bylymphocytes

in response to the presence of foreignsubstances, called antigen in our body

2)Lymphocytes (WBC) :

-found in lymph nodes & in the blood circulatorysystem

-2 types :

B- lymphocyte T-lymphocytesSecretes antibody Helps B-lymphocytes

in antibody

production

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3)Antigen

-is a substance (usually protein) normally found

on the outer surface of pathogen.-different types of pathogen act as different types

of antigen.

4)It is a specific defence because when a specificantigen invades the body, lymphocytes isstimulated & produces specific antibodytodestroy these specific antigens.

5)This response is known as immune responsebecause it resists the body from pathogens ordisease

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6) After any infection, some lymphocytesremain in the body as memory cells, which

may last for several months /years.#This memory cells help to defend the body

against next infection by the same

antigen.#During this period, someone is said to be

immuned for that particular disease.

7) Definition of immunity

The ability of an organism to defend

itself against infection by pathogens.

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Types of Immunity