11 2 THE BODYS LINE OF DEFENSE PAGES

11. 2 THE BODY’S LINE OF DEFENSE PAGES 357 - 366 Biology 20 Unit D

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)

Parasites Head Lice (adult stage) Malaria: Singlecelled protozoan parasites of the genus Plasmodium. Four species infect humans by entering the bloodstream. Giardia: a fungi that infects the intestines of animals causing “beaver fever”. People most often get it from drinking contaminated water

TAPEWORMS, RINGWORMS, AND OTHERP ATHOGENS

VIRUSES Influenza Virus (Flu) Human Immunodeficiency Virus (AIDS)

BACTERIA Salmonella typhimurium (Food Poisoning) Syphilis- is an infectious venereal disease caused by the spirochete Treponema pallidum

I. ) FIRST LINE OF DEFENCE: NONSPECIFIC AND EXTERNAL (P 357) Skin – protective � Acidic secretions (p. H of 3 – 5) Respiratory tract (windpipe) – mucus and cilia sweep foreign material away from lung Stomach – acids and protein digesting enzymes destroy microbes Tears, saliva, mucous secretions – lysozyme (enzyme) destroys bacterial cell walls

II. ) SECOND LINE OF DEFENCE – NONSPECIFIC AND INTERNAL (P 357) A. Phagocytes (WBC’s) destroy microbes

TYPES OF PHAGOCYTES

Phagocytosis �Ingestion of invading microbes by certain WBCs

� Pus - remaining fragments of protein, dead WBCs, digested invader

B. INFLAMMATORY RESPONSE Tissue damage due to physical injury Initiates an inflammatory response Nonspecific response that results in swelling, heat, and pain Clues to second line of defence: �Pus �Inflammation

C. FEVER – EXAMPLE OF SYSTEM WIDE RESPONSE TO INFECTION Neutrophils and macrophages digest invaders �Release chemicals Reach hypothalamus Reset body temperature to about 40 OC Fever makes it difficult for harmful bacteria to survive �Fevers 40 OC can be unsafe Enzymes start to denature

D. PROTECTIVE PROTEINS - prevent multiplication of bacteria and viruses i) complement � active against bacteria once activated, some complements form pores in bacterial cell walls and membranes pores allow salts and fluids to enter bacterial cell bacterium expands until it bursts

E. INTERFERON active against viruses tissue cells infected by viruses produce and secrete interferon chemical binds to uninfected cells these cells now produce substances that interfere with viral replication

III. ) THE IMMUNE RESPONSE (THE THIRD LINE OF DEFENCE) slower, but more specific white blood cells and lymph system are involved WBC respond to antigens: any substance recognized as foreign to the body often antigens are part of a bacterial cell wall, viral coat, or foreign cell membrane

CELLS OF THE IMMUNE SYSTEM OVERVIEW:

Immune system detects an antigen T-cells multiply which attack the invader directly called cell-mediated immunity: cells move thru blood and lymph target: bacteria, viruses, etc. that have toxins infected host cells; cancer cells, implanted tissues B-cells multiply which produce antibodies Called antibody mediated immunity: antibodies move thru blood and lymph target: free bacteria, viruses, and in body fluids

1. CELL-MEDIATED IMMUNITY a macrophage engulfs a bacterium, then the bacterial antigen, along with an identification protein, will be displayed on the macrophage membrane appropriate T-cell and its receptor is presented with the antigen, and is now activated T-cell then grows and divides into the following: a) Helper T-cell directly stimulates a B-cell by presenting an antigen to it

b) Killer T-cell release a chemical which forms a pore in foreign cell membrane bearing an antigen; cell swells and bursts c) Suppressor T-cells number increases slowly suppress immune response d) Memory T-cells recognizes original invading antigen; can last a life-time lymphokines: chemicals which stimulate immune cells to divide

2. ANTIBODY-MEDIATED IMMUNITY B-cells produce antibodies: proteins which combine with and inactivate antigens antigen binds to membrane-bound antibody on B-cell divides into: 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

SUMMARY OF 3 RD LINE OF DEFENCE