C 3.2

Pathogen

Organism that causes infectious diseases.

Host

The organism that is infected and develops the disease.

Main groups of pathogens

Viruses, bacteria, fungi, and protists.

Eubacteria

The type of bacteria that cause diseases in humans.

Archaea

Other domain of bacteria not known to cause infectious diseases in humans.

Surface barriers to infection

Includes skin and mucous membranes.

Sebum

A chemical secreted by sebaceous glands that makes the skin acidic.

Mucous membranes

Thin, soft areas of skin kept moist with mucus, found in areas such as the nose and trachea.

Phagocytes

Cells that ingest pathogens for non-specific immunity.

Clotting factors

Substances released by platelets that initiate the clotting process.

Thrombin

Enzyme that converts fibrinogen to fibrin.

Innate immune system

Non-specific immune response that does not change during an organism's life.

Adaptive immune system

Specific immune response that develops over an organism's life.

Antigens

Foreign substances that stimulate the production of antibodies.

Lymphocytes

White blood cells part of the adaptive immune system; includes B and T cells.

HIV (Human Immunodeficiency Virus)

A retrovirus that attacks Helper T-lymphocytes and causes AIDS.

AIDS (Acquired Immune Deficiency Syndrome)

Condition resulting from HIV, characterized by a reduced immune response.

Antibiotics

Chemicals that block processes occurring in bacteria but not in eukaryotic cells.

Zoonosis

Infectious diseases that can transfer from other species to humans.

Vaccination

The use of a vaccine to trigger immunity.

Herd immunity

Resistance to the spread of a contagious disease within a population that results when a sufficiently high proportion of individuals are immune.

Primary immune response

The initial response of the immune system to a pathogen.

Secondary immune response

A faster and stronger immune response elicited by memory cells upon re-exposure to an antigen.