Unit 5: Factors Affecting Human Health (Part 2) - Immune System

Vocabulary flashcards covering lines of defense, natural barriers, non-specific immune responses, humoral and cell-mediated specific immune responses, and vaccines.

Immune System

A collection of white blood cells, organs, and molecules that protects the body by detecting harmful microorganisms, destroying pathogens, remembering previous infections, and maintaining health and homeostasis.

First Line of Defense

The level of defense consisting of natural barriers that prevent pathogens from entering the body.

Mechanical Barrier

A physical natural barrier, such as skin, that acts to prevent microorganisms from entering the body.

Chemical Barrier

A secreted natural barrier—such as sweat, tears, saliva, and gastric juices (stomach acid)—that contains enzymes or acidic conditions to destroy pathogens.

Mucous Membrane

A natural barrier lining the respiratory and digestive tracts that traps pathogens to prevent their entry into body tissues.

Second Line of Defense

A rapid, non-specific immune response present from birth that activates when pathogens penetrate natural barriers, involving inflammatory reactions and phagocytosis.

Inflammatory Reaction

A set of non-specific defense reactions involving white blood cells (macrophages) that defend the organism against external aggressions to reduce or stop their effect.

Redness and Heat

Signs of an inflammatory reaction caused by the dilation of blood capillaries at the site of infection or injury.

Edema

Swelling that occurs as a sign of inflammation due to a massive leak of plasma out of blood capillaries into surrounding tissue.

Phagocytosis

The process in which phagocytes surround, engulf, and break down pathogens using lysosomes.

Steps of Phagocytosis

The four sequential stages of phagocytosis: A: Attraction, B: Ingestion (forming a phagosome via pseudopods), C: Digestion (forming a phagolysosome), and D: Exocytosis (excreting bacterial debris).

Third Line of Defense

The specific immune response that takes place when non-specific immune responses fail to eliminate pathogens, mediated by mature B lymphocytes and T cells.

B Lymphocytes

White blood cells produced in the bone marrow that mature to secrete antibodies into the blood or lymph, mediating humoral immune response.

T Lymphocytes

White blood cells produced in the bone marrow and matured in the thymus (also called killer cells) that mediate cell-mediated immune response.

Humoral Immune Response

A specific immune response carried out by B lymphocytes that release antibodies into plasma or blood to target pathogens and toxins outside cells.

Cell-Mediated Immune Response

A specific immune response carried out by T cells targeting infected body cells, cancer cells, and transplanted cells.

Plasma Cell

A mature B cell that secretes millions of antibodies specifically designed to combine with the triggering antigen into the blood or lymph.

Antibody

A Y-shaped protein with two binding sites, produced by activated B lymphocytes (plasma cells), that specifically binds and neutralizes non-self antigens.

Antigen

Any molecule or particle recognized by the immune system as foreign or non-self that triggers an immune response.

Seropositive Individual

An individual whose serum contains antibodies secreted by mature B lymphocytes against a specific antigen.

Seronegative Individual

An individual whose serum does not contain antibodies secreted by mature B lymphocytes against a specific antigen.

Helper T Cells

T lymphocytes ($T_h$) that recognize antigens presented on antigen-presenting cells (APCs) and become activated to signal and coordinate other immune cells, such as B cells and cytotoxic T cells.

Cytotoxic T Cells

Killer T cells ($T_c$) that recognize infected body cells presenting viral antigens on their surface and destroy them directly.

Cytotoxins

Toxic substances contained in cytoplasmic granules of cytotoxic T cells—specifically perforin and granzymes—that destroy target infected cells.

Perforin and Granzymes

Cytotoxins released by cytotoxic T cells: perforin forms a channel in the target cell membrane, through which granzymes enter to induce death of the infected cell.

Secondary Immune Response

The rapid and robust immune response that occurs upon secondary encounter with a pathogen due to pre-existing memory cells formed during the primary response.

Vaccine

An inactivated or weakened form of a pathogen (or component of it) administered to induce a specific immune response and create memory cells without causing severe disease.