PathogensPathogens Microorganisms c

ausing diseases eg. bacteria

viruses fungi protozoa

Importance of having Importance of having Body Defense SystemBody Defense System

prevent pathogens from entering the body

kill or inactivate any pathogens that gain entry into the body

Ways of Pathogen Ways of Pathogen spreading spreading

In Droplets e.g. influenza, cold By Touch

e.g. boils, athlete’s foot, AIDS, anthrax

By Dust e.g. diphtheria, scarlet fever, anthrax, hay fever

In Faeces e.g. cholera, hepatitis A

In Food e.g. salmonella

By Insect e.g. malaria

By Vertebrates e.g. rabies

Ways of Pathogen Ways of Pathogen spreading spreading

Nonspecific Nonspecific DefencesDefences

• physical barrier Skin the 1st line of defence of pathogen Ciliated & Mucus Lining of

respiratory tract mucus: trap bacteria beating cilia: waft the trapped

bacteria towards the throat

BarriersBarriers

• chemical barrier sebaceous glands of skin produce oily secretion (sebum) whic

h has antiseptic properties tears & saliva contain lysozymes (enzyme) which d

estroy bacteria

BarriersBarriers

gastric juice in stomach contain acid which can destroy

most bacteriaacid secretions in vagina of

womenreduce growth of pathogens

• chemical barrier

BarriersBarriers

When you cut yourself carelessly, why the wound stop bleeding after a while ?∵Blood Clotting occurs: Platelets release a substance to turn soluble fibrinogen into insoluble fibrin which catches blood cells & seal off the cut

Insolublefibrin

BLOOD CLOTTINGBLOOD CLOTTING is is important because this important because this can …can … Prevent the body from

invasion of pathogens

Stop excess bleeding (blood loss)

Nonspecific Nonspecific (after (after

infection)infection)• to localize & destroy the pathogens• phagocytes involve in phagocytosis

– to engulf and digest the pathogens

macrophage

• inflammatory response

– (before inflammation : skin arterioles constrict to prevent excessive bleeding)

– skin arterioles in the infected area dilates so that more blood flows to the area

– the permeability of skin capillaries increases so that more phagocytes & fluid come into the infected tissues

– the skin becomes red & swell up with pain (because of high pressure)

Nonspecific Nonspecific (after (after

infection)infection)

Specific Specific DefencesDefences

What are Specific What are Specific Defences ?Defences ?When a pathogen is able to get past the nonspecific defences, immune responses will be produced which involve a series of specific defences

• After pathogens get into the blood & lymph :• Antigens on the surface of pathogen stimulate

lymphocytes in the lymph nodes and the blood.

– to produce specific antibodies which kill pathogen by :

» lysis - burst the pathogen» clump the pathogen together

• After pathogens get into the blood & lymph :• Antigens on the surface of pathogen

stimulate lymphocytes

– to produce specific antibodies which kill pathogen by :

» stick to the surface of pathogen,so that phagocytes can ingest them easily (enhanced phagocytosis)

» neutralize the toxins from pathogens

Primary & Primary & Secondary Secondary Immunity Immunity ResponsesResponses

Primary Response: the 1st

time invaded by a certain

pathogen which stimulates

the body to produce

antibodies

Primary & Primary & Secondary Secondary Immunity Immunity ResponsesResponses

Secondary Response: the invasion

of the same type of pathogen

which stimulates lymphocytes to

produce much larger amount of

antibodies & much more quickly

Time (days)

antibodyconc.

immune response

no immune response

primaryresponse

secondaryresponse

second exposureto antigen X

first exposureto antigen X

Small pox (a killing disease)

Vaccine Vaccine (Vaccination)(Vaccination)

Vaccine (Vaccination)Vaccine (Vaccination) From dead / weakened pathogens

– to stimulate the lymphocytes to produce antibodies

Times of injection:– first→ second → (booster) injection

From injection of a serum It belongs to acquired immunity

Injection of a SerumInjection of a Serum

immune response

no immune response

antibodyconc.

Time (days)injection of antibody

(in serum)

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