Paramedic Care:Principles & Practice Volume 1Introduction to Advanced Prehospital Care
Chapter 8 General Principles of Physiology and Pathophysiology
Part 3 Topics • Self-Defense Mechanisms • The Immune Response • Inflammation • Variances in Immunity and Inflammation • Stress and Disease
Self-Defense Mechanisms • The body has powerful ways of defending and healing itself. • Homeostasis • Occasionally, these natural defense mechanisms are unequal to the task and become overwhelmed.
Infectious Agents • Bacteria • Single-cell organisms with a cellmembrane and cytoplasm but no organized nucleus • Prokaryotic cell • Cause many common infections, and usually respond to antibiotic treatment • Two types of toxins produced by bacteria: • Exotoxins and Endotoxins
Infectious Agents • Bacteria (cont.) • The systemic spread of toxins through the bloodstream is known as septicemia. • The body counters the bacterial invasion and release of enzymes and toxins through activation of the immune system. • Macrophages • Pyrogens
Infectious Agents • Viruses • Much smaller than bacteria • They cannot grow without the assistance of another organism • Intracellular parasites • If the virus does not find a host cell, it will die • Has no organized cellular structure • Capsid • Envelope
Infectious Agents • Viruses (cont.) • Symptoms of a virus may not be readily apparent • May remain dormant within a cell for months or years • Viruses are very difficult to treat • Infected cell must be destroyed which affects healthy cells • Viruses mutate • Generally, symptomatically treated
Other Agents of Infection • Fungi • Rarely cause human disease other than minor skin infections. • In the immuno-compromised patient, the fungi can invade the lungs, blood, and several organs. • Parasites • Range in size from protozoa (single-cell animals not much larger than bacteria) to large intestinal worms
Other Agents of Infection • Prions • Most recently recognized classification of infectious agents • Initially thought to be slow-acting viruses • They are smaller, are made entirely of proteins, and do not have protective capsids
Three Lines of Defense • Anatomical Barrier • The body’s natural anatomical barrier is the epithelium • Provides both physical and chemical protection • Anatomical defenses are external and nonspecific
Three Lines of Defense • Inflammatory Response • Inflammation begins within seconds of injury or invasion by a pathogen • It is nonspecific • Mediated by multiple plasma protein systems • Complement system, the coagulation system, and the kinin system
Three Lines of Defense • Immune Response • The immune response is specific • It will develop a specialized response for each different invader • Mediated by just one plasma protein system • Immunoglobulin • Attacks the invader mainly with a single cell type • Lymphocyte
Overview of the Immune Response • Most viruses, bacteria, fungi, and parasites have proteins on their surface called antigens. • Determined to be either “self” or “non-self” • Antibodies combine with antigens and destroy them. • Memory cells “remember” the antigen and destroy it more quickly if exposed again.
Characteristics of the Immune Response and Immunity • The immune response and immunity can be classified in various ways: • Natural versus acquired immunity • Primary versus secondary immune responses • Humoral versus cell-mediated immunity
Natural vs. Acquired Immunity • Natural immunity is part of geneticmakeup. • Acquired immunity develops as anoutcome of the immune response. • Active immunity is generated by the immune system after exposure to an antigen. • Passive immunity is transferred to a person from an outside source.
Primary vs. Secondary Immune Responses • Primary immune response • The initial development of antibodies in response to the first exposure to an antigen • Secondary immune response • The swift, strong response of the immune system to repeated exposures to an antigen
Humoral vs. Cell-Mediated Immunity • Humoral immunity is the long-term immunity to an antigen provided by antibodies produced by B lymphocytes. • Cell-mediated immunity is short-term immunity to an antigen provided by T lymphocytes.
B Lymphocytes • White blood cells • Respond to antigens and produce antibodies that attack the antigen • Develop a memory for the antigen • Confer long-term immunity to specific antigens
T Lymphocytes • White blood cells • Do not produce antibodies • Recognize the presence of a foreign antigen and attack it directly
Lymphocytes and the Lymph System • Lymphocytes are circulated throughout the body as part of the lymph system. • B lymphocytes, T lymphocytes, secretory lymphocytes • Lymph consists primarily of interstitial fluid carrying proteins, bacteria, and other substances.
Lymphocytes and the Lymph System • Lymph is carried through lymphatic vessels that are parallel but separate from blood vessels. • Two lymph ducts in thorax: • Right—the smaller drains the right arm, right head, and right side of thorax • Thoracic duct—larger, in the left thorax, drains the rest of the body
Lymphocytes and the Lymph System • The ducts drain lymph into the right and left subclavian veins. • The B lymphocytes and T lymphocytes carried by the blood and the lymph system are the key elements in humoral and cell-mediated immunity.
Induction of the Immune Response • Antigens and Immunogens • Antigens that are able to trigger the immune response are immunogens. • Not every antigen can trigger an immune response. • If an immune response is triggered, it is immunogenic.
Characteristics of Antigenic Immunogenicity • Sufficient foreignness • Sufficient size • Sufficient complexity • Presence in sufficient amounts
Histocompatibility Locus Antigens • The body recognizes if a substance is self- or non-self as a result of certain antigens that are present on almost all cells of the body except red blood cells. • Determines compatibility of tissues and organs that will be grafted or transplanted from a donor
Blood Group Antigens • HLAs are not present on red blood cells. • Red cell antigens have been grouped into a number of different blood group systems. • The two groups that trigger the strongest immune response are the Rh system and the ABO system.
The Rh System • Rh factor is present in about 85 percent of North Americans. • Present—Rh positive • Absent—Rh negative • Problems may occur with pregnancy • Usually with the second pregnancy • Incompatibility can cause severe problems • Hemolytic disease in infants
The ABO System • The ABO blood group consists of only two antigens named A and B. • People with blood type A carry A antigens. • People with blood type B carry B antigens. • People with blood type O carry neither antigen.
Type A and BImmune Responses • An immune response will be activated if a person with blood type A receives type B blood. • B anti-bodies will be present • The same will occur if a person with type B blood receives type A blood. • A anti-bodies will be present
Universal Donor and Recipient • People with blood type O have no antigens to trigger an immune response. • This is the universal donor • People with blood type AB have both antigens and will not have an immune response. • This is the universal recipient
Humoral Immune Response • Long-lasting response provided by production in the bloodstream of antibodies and memory cells called B lymphocytes • Also called the internal or systemic immune system • Another kind of humoral immunity is provided by secretions at the body surfaces • External, mucosal, or secretory immune system
B Lymphocytes • Lymphocytes are generated from stem cells. • May take one of two paths as they mature: • May travel through the thymus gland and mature into T lymphocytes • May travel through a set of lymphoid tissues, including the spleen and lymph nodes, and mature into B lymphocytes
B Lymphocytes • Clonal diversity is generated as the precursors of mature B cells develop in the bone marrow. • The B cell precursor develops receptors for every possible type of antigen it may encounter.
B Lymphocytes • Clonal selection occurs when a specific antigen reacts with the appropriate receptor on the surface of immature B lymphocytes. • The immature B cell will proliferate and differentiate. • Plasma cells will secrete immunoglobulins. • This process takes 5-7 days following exposure.
Immunoglobulins and Antibodies • Antibodies are proteins secreted by plasma cells that are produced by B cells in response to an antigen. • The shape of the antigen fits the shape of the antigen-binding site on the immunoglobulin (antibody) molecule like a key in a lock.
The Functions of Antibodies • An antibody circulates in the blood or is suspended in body secretions until it meets and binds to a specific antigen. • Antigen-antibody complexes form from the direct and indirect binding of antibodies and antigens. • The end result is destruction or inactivation of the antigen.
The Functions of Antibodies • Direct effects of antibodies on antigens • Agglutination • A soluble antibody combines with a solid antigen causing it to clump together • Precipitation • The antigen-antibody complex precipitates out of the blood and is carried away by body fluids • Neutralization • The antibody inactivates the antigen by preventing it from binding to receptors on the surface of cells
The Functions of Antibodies • Indirect effects of antibodies on antigens • Enhancement of Phagocytosis • Certain types of white blood cells that ingest and digest foreign substances • Activation of Plasma Proteins • Antibodies can activate plasma proteins of the complement system that attack and destroy antigens.
Functions of Antibodies • Neutralization of bacterial toxins • Antibodies neutralize the bacterial toxins by occupying their antigenic determinant sites. • Neutralization of viruses • Antibodies attach to viruses, causing agglutination or fostering phagocytosis. • Opsonization of bacteria • Coats the bacteria with opsonin, a substance that makes them vulnerable to phagocytosis. • Activation of the inflammatory processes
IgM Produced first IgG Has “memory” Responsible for agglutination, precipitation, and complement activation IgA Involved in secretory immune responses IgE Involved in allergic reactions IgD Present in very low concentrations Classes of Immunoglobulins
Antibodies as Antigens • An antibody in the human body can function as an antigen if it enters the body of another person. • Human Antibody Classifications • Isotypic • Same within same species • Allotypic • Differ between members of same species • Idiopathic • Differ within the same individual
Secretory Immune System • Its primary function is to protect the body from pathogens that are inhaled or ingested. • Tissues secrete substances such as sweat, tears, saliva, mucus, and breast milk.