11.2 The Body’s Line of Defense - PowerPoint Presentation

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11.2 The Body’s Line of DefensePages 357 - 366

Biology 20 Unit D

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11.2 The Body’s Line of Defence

Pathogen:

an organism causing disease

An infectious disease may be caused by:

Viruses, bacteria, fungi, protozoa, flatworms and roundworms

Staphylococcus

aureus

can be pathogen in the right conditions on the surface of the skin (causing impetigo and other skin conditions)

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Parasites

Malaria

: Single-celled protozoan parasites of the genus

Plasmodium

. Four species infect humans by entering the bloodstream.

Head Lice (adult stage)

Giardia

: a fungi that infects the intestines of animals causing “beaver fever”. People most often get it from drinking contaminated water

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Tapeworms, ringworms, and other Pathogens

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Viruses

Influenza Virus (Flu)

                                                                     

Human Immunodeficiency Virus (AIDS)

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Bacteria

Salmonella

typhimurium

(Food Poisoning)

Syphilis

- is an infectious venereal disease caused by the spirochete

Treponema pallidum

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Elephantitis

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I.) First Line of Defence:

nonspecific

and external (P357

)

Skin – protectiveAcidic secretions (pH of 3 – 5) Respiratory tract (windpipe) – mucus and cilia sweep foreign material away from lung

Stomach – acids and protein digesting enzymes destroy microbesTears, saliva, mucous secretions –

lysozyme

(enzyme) destroys bacterial cell walls

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II.) Second Line of Defence

– nonspecific and internal (P357)

A. Phagocytes

(WBC’s) destroy microbes

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Types of Phagocytes

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Phagocytosis

Ingestion of invading microbes by certain WBCs

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Pus

- remaining fragments of protein, dead WBCs, digested invader

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B. INFLAMMATORY RESPONSE

Tissue damage due to physical injury Initiates an inflammatory responseNonspecific response that results in swelling, heat, and pain

Clues to second line of defence:

Pus

Inflammation

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C. Fever – example of system wide response to infection

Neutrophils

and macrophages digest invaders

Release chemicals

Reach hypothalamusReset body temperature to about 40OCFever makes it difficult for harmful bacteria to survive

Fevers  40O

C can be unsafe

Enzymes start to denature

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D. Protective Proteins

- prevent multiplication of bacteria and virusesi) complement

active against

bacteria

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E. interferon

active against viruses

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III.) The Immune Response

(The Third Line of Defence)

slower, but

more specific

white blood cells and lymph system are involvedWBC respond to antigens: any substance recognized as foreign to the bodyoften antigens are part of a bacterial cell wall, viral coat, or foreign cell membrane

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Cells of the Immune System Overview:

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Called antibody mediated

immunity: antibodies move thru blood and lymph

called cell-mediated immunity:

cells move thru blood and lymph

Immune system detects an antigen

T-cells multiply which

attack the invader directly

B-cells multiply which produce antibodies

target: bacteria,

viruses, etc. that have toxins infected host cells; cancer cells, implanted

tissues

target: free bacteria, viruses, and in body fluids

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1. Cell-Mediated Immunity

a macrophage engulfs a bacterium, then the bacterial antigen, along with an identification protein, will be displayed on the macrophage membraneappropriate T-cell and its receptor is presented with the antigen, and is now activatedT-cell then grows and divides into the following:

a)

Helper T-cell

directly stimulates a B-cell by presenting an antigen to it

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b) Killer T-cell

release a chemical which forms a pore in foreign cell membrane bearing an antigen; cell swells and burstsc) Suppressor T-cellsnumber increases slowly

suppress immune response

d) Memory T-cells

recognizes original invading antigen; can last a life-timelymphokines: chemicals which stimulate immune cells to divide

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2. Antibody-Mediated Immunity

B-cells produce antibodies: proteins which combine with and inactivate antigens

antigen binds to membrane-bound

antibody on B-cell

many plasma cells which produce and release antibodies into blood and lymph

memory B-cells that remain in bloodstream

antibody level increases,

and antigens disappear from body

B-cell divides into:

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Summary of 3rd Line of Defence