Chapter 20: The Immune System
The immune system has two intrinsic systems:
1. Innate (nonspecific) defense system
2. Adaptive (specific) defense system
The immune system is a functional system rather than structural; there are no specific immune system organs
Pathogen: a disease-causing agent; anything foreign in our body that causes disease
Three lines of defense:
1st: external barriers
2nd: several non-specific defense mechanisms
3rd: immunity, specific resistance to disease
Innate Defenses (pp. 691–700)
1st line of defense - Surface Barriers: Skin and Mucosae • Protective chemicals inhibit or destroy microorganisms • Skin, a highly keratinized epithelial membrane, represents a physical barrier to most microorganisms and their enzymes and toxins (skin acidity = acid mantle) • Mucous membranes line all body cavities open to the exterior and function as an additional physical barrier. • Secretions of the epithelial tissues include acidic secretions (HCl, hydrochloric and protein-digesting enzymes of stomach mucosae), lipids in sebum, dermcidin in sweat, lysosome of saliva, lacrimal fluid in tears, and mucus (produced by goblet cells of mucous membranes). • Respiratory system modifications: mucus-coated hairs in the nose; cilia of upper respiratory tract sweep dust-and-bacteria-laden mucus from lower respiratory passages B.
2nd line of defense - Internal Defenses: Cells and Chemicals The second line of defense is necessary if microbes invade deeper tissues 1.
Phagocytes (giant eating cells) confront microorganisms that breach the external barriers. • Mechanisms of phagocytosis: Adherence of phagocyte to pathogen … facilitated by opsonization (coating of pathogen by complement proteins or antibodies); and destruction of pathogens (acidification and digestion by lsysosomal enzymes; respiratory burst with the release of cell-killing free radicals and activation of additional enzymes; oxidizing chemicals and defensins in neutrophils). a.
Macrophages are the main phagocytes of the body. They develop from monocytes to become the chief phagocytic cells in search of foreign invaders. Two types: Free macrophages wander through tissue spaces (alveolar macrophages); and Fixed macrophages are permanent residents of some organs (Kupffer cells of the liver; microglia in the brain); b.
Neutrophils are the first responders and become phagocytic when they encounter infectious material. c.
Eosinophils are weakly phagocytic but are important in defending the body against parasitic worms. d.
Mast cells have the ability to bind with, ingest, and kill a wide range of bacteria. 2.
Natural killer cells (innate, nonspecific) are able to lyse and kill cancer cells and virally infected cells before the adaptive immune system has been activated; (the pit bulls of the defense system); large granular lymphocytes; target cells that lack “self” cell-surface receptors; induce apoptosis in cancer cells and virus-infected cells (self-killing of cell; programmed cell death); secrete potent chemicals that enhance the inflammatory response 3.
Inflammation (the most important mechanism – macrophages, mast cells, WBCs and inflammation chemicals) occurs any time the body tissues are injured by physical trauma, intense heat, irritating chemicals, or infection by viruses, fungi, or bacteria.
Benefits of inflammation:
1) prevents the spread of damaging agents
2) disposes of cell debris and pathogens
3) sets the stage for repair
The four cardinal signs of acute inflammation are redness, heat, swelling, and pain (and sometimes impairment of function) ---
Chemicals cause dilation of surrounding blood vessels to increase blood flow to the area and increase permeability, which allows fluid containing clotting factors and antibodies to enter the tissues....
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