Infectious disease is caused by an organism entering the body and multiplying inside its host.

Pathogens: Disease causing organisms.

Toxin: poisonous substance that disrupts the metabolism of the infected organism.

Bacteria

endotoxins: part of the cell wall. Symptoms include fever, weakness, and damage to the circulatory system.

exotoxins: products of the metabolism of some bacteria..

Viruses: interfere with cell’s metabolism and lyse cell after producing new viruses.

Protozoa: often parasites, such as Entamoeba, Plasmodium.

Fungi: produce toxins; may be parasitic.

Mechanisms of Transmission

Air: spores, cysts, droplets.

Water: waste contamination.

Contact: direct (person-to-person); indirect (inanimate object involved).

Vectors: pathogen is carried by another organism and transmitted to a new host.

Koch’s Postulates

Isolate suspected organism.

Grow organism in lab culture.

Inoculate a healthy animal with cultured organism. Observe.

Isolate the organism that caused the disease in the experimental animal. Compare it with the one isolated previously.

The Immune System: Non-specific Defense

General defense that acts against anything non-self.

Species Resistance: genetic characteristics of a species provide defense against certain pathogens.

Mechanical barriers (first line of defense)

Skin: layers of dead cells; poisonous chemical substances; harmless bacteria.

Mucous membranes: line nasal and oral passages to trap microorganisms.

Chemical barriers

Enzymes: pathogens reaching the stomach are destroyed by powerful chemicals.

Lysozyme: enzyme found in urine, tears, and saliva. Protects openings of skin.

Interferon: produced by infected cells in response to viral infection.

Inflammation: reaction to tissue damage. Warmth, pain, itching, reddening, swelling. (second line of defense)

Histamine: dilates arteries

Cytokines: makes capillary walls leaky to allow white blood cells to enter tissue spaces.

The Immune System: Specific Defense

Components of the immune system attack specific pathogens by identifying surface proteins (antigens) of the pathogen.

Primary response

T cells: attack antigens in a cell-mediated response. Some remain as memory cells to attack if the antigen is encountered again.

B cells: produce antibodies that bind to and destroy antigens.

Secondary response: memory T and B cells multiply when host is invaded again.

The Immune System

Natural immunity: present at birth.

Acquired immunity: developed after birth.

Active immunity: developed as a result of one’s own immune system responding to a harmful agent.

Developed naturally

As a result of vaccination

Passive immunity: developed in another organism and passed on to another.

Received by fetus from mother

Injection

The Lymphatic System

Lymph: fluid in lymph vessels.

Lymph vessels transport lymph to the circulatory system.

Lymph nodes: filters located along lymph vessels that remove bacteria and foreign particles from lymph. Lymphocytes destroy bacteria.

Lymphatic organs

Tonsils

Spleen

Thymus

The Immune System: Plants

Tannins

Bud tissues - protection against freezing.

Leaf tissues - serve to reduce palatability and, thus, protect against predators.

Root tissues - act as a chemical barrier to penetration and colonization of roots by plant pathogens.

Seed tissues - have bactericidal properties.

Stem tissues - may have a role in the growth regulation. contribute to the natural durability of wood by inhibiting microbial activity.

Secondary compounds: compounds not directly related to the growth and development of a plant. Used to protect plant from herbivores.

Stored in vacuoles in the plant cell; released when the cell is crushed or broken.

Usually have a bitter taste to discourage predators.

May cause a change in the herbivore, such as caffeine and morphine.

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