The Nature of Disease
 Pathogens
 Disease producing agents, such as, bacteria, viruses, protozoans, fungi & other parasites
 Infectious disease
 Any disease caused by the presence of pathogens in the body

The Nature of Disease

Koch’s postulates of 1884
(a procedure to establish the cause of a disease)
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1) A pathogen must be found in the body of a sick organism
2) The pathogen must be isolated & grown in the lab to produce a culture
3) When the cultured pathogen is placed in a new host, it should cause the same disease
4) The pathogen should be isolated from the new host and shown to be the original pathogen

The Nature of Disease
 Endemic disease
 Disease that are constantly present in a population (ex: common cold)
 Epidemic
 When many people in a given area are affected with the same disease at about the same time (ex: influenza)

The Nature of Disease
 Antibiotics
 Substances produced by microorganisms that, in small amounts, will kill or inhibit the growth
& reproduction of other microorganisms
 Ex: Penicillin, an antibiotic produced by a fungus, has been in use for over 50 years; many microorganisms are now resistant to penicillin

The Immune System
 Innate Immunity
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Your body’s own built-in defense system
 First (& best) line of defense:
– Unbroken skin
– Body secretions, such as mucus, tears, sweat, & saliva

The Immune System
 Second line of defense is inflammatory response:
 Fever = increased body temperature slows or stops the growth of pathogens
 Phagocytes = white blood cells, such as macrophages , that destroy pathogens
 Interferon = proteins that protect cells from viruses

The Immune System
 Third line of defense is cellular immunity:
 Lymphocytes are types of white blood cells that defend the body against foreign substances
 T cells are lymphocytes that defend against abnormal cells & pathogens inside livings cells
 B cells are lymphocytes that provide immunity against antigens & pathogens in the body fluids

The Immune System
 Lymph
 Tissue fluid (to bathe, nourish cells) after it enters the lymph vessels that will return it to the blood
 Lymph nodes
 Glands that filter pathogens from the lymph before it returns to the bloodstream

The Immune System
 Acquired Immunity
 Defending against a specific pathogen by gradually building up a resistance to it.
 Passive = acquired naturally when antibodies are transferred from mother to unborn child through the placenta
 Active = acquired artificially when induced by vaccines

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