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Transcript
Lec 6 Nov.2016 Immune System Immunity: is defined as the ability of human body to resist against harmful chemicals such as toxins that released by microorganism which tend to damage the tissues & organs. Lymphocytes are key constituents of the immune system. The lymphatic system includes lymphocytes, lymph nodes, tonsils, spleen, thymus gland, lymph and lymphatic vessels. Lymphatic system plays an important role in protecting us against invading microorganism and other harmful substances \\ : 2 Types: 1. Innate immunity. 2. Acquired (adaptive) immunity. A. Innate immunity: in this type of immunity the body is born with the ability to recognize and destroy certain substances but cannot distinguish among different kinds of bacteria and remember previous encounters. Its components are: 1.mechaical mechanisms. 2. Chemical mediators. 3. Cells 4. Inflammation. 1. Mechanical mechanisms: such as skin and mucous membranes form barriers that prevent the entry of chemicals and microorganisms into the tissues of the body. For example, substances are washed from the eyes by the tears, from the mouth by saliva, and from the urinary tract by urine. 2. Chemical mediators: a. acid secretion such as HCL in the stomach and sebum in skin that kill and prevent microbial growths. b.lysozymes in tears, saliva, nasal secretions and sweat that lyses cells. c. histamine prostaglandins, complements and leukotriens that promote inflammation by attracting leukocytes and stimulating phagocytes. d. the other chemical mediator is pyrogens released by neurophils and monocytes that stimulate fever production, which inhibit microorganism growth. 3. Cells: such as neutrophils, basophiles, esohophils, mast cells, monocytes and natural killer cells (are a type of lymphocytes) which are involved in phagocytosis and production of chemicals that participate in the response of immune system. 4.Inflammation: when the tissue injury occurs either by bacteria or chemical there is a release of chemical mediators (also called chemotaxins or chemotactic factors ) from infected area which attract leukocytes especially neutrophils to the infected area.. The process of attraction is called chemotaxis. The leukocyte leaves the walls of 2 3 capillaries to the infected area by a process called diapedesis. The chemotaxins produce several effects: 1. Vasodilatation. 2. Increased vascular permeability resulting in edema 3.large amount of fibrinogen enter into interstitial space from blood and converted into fibrin (clot) which prevents the spread of infection by ''walling off” the infected area. The “walling off” process delays the spread of bacteria or toxic products. The process of killing bacteria continues by neutrophils, and macrophages until all bacteria or foreign substances are destroyed. The process of ingestion and digestion of foreign microorganism by macrophages is called phagocytosis. 3 4 4 5 Types of inflammation: a. localized: which is confined to a specific area of the body. b. systemic: this occurs in many areas of the body. So one of the results of inflammation is to “wall off” the area of injury from remaining tissues. Signs and symptoms of inflammation: are heat, redness, , swelling, pain ,loss of function, and release of chemicals called pyrogens from leukocytes which cause fever and inhibit growth of microorganism. Pus formation: are dead neutrophils, necrotic tissue, and dead macrophages and tissue fluid. A localized collection of pus is called abscess. B. Acquired or adaptive immunity: can recognize and remember a particular substance. Vaccination is an example of acquired immunity e.g. typhoid fever, measles, tetanus. Substances that activate adaptive immunity are antigens which are large molecules with a molecular weight of 10000 or more for example penicillin. Antigens are proteins or large polysaccharides. There are two types of antigens: a. foreign antigens: are not produced by the body but are introduced from outside it. Pollen, food, drugs and dried skin are foreign antigens that cause allergic reaction. Transplanted organs and tissues that contain foreign antigens result in the rejection of the transplant organs. b.Selfantigens: that produced by the body itself. There are two types of acquired immunity: 1. Humoral immunity. 2. Cellular immunity. Humoral immunity: is mediated by B-lymphocytes which are produce plasma cells. Plasma cells produce circulating antibodies or immunoglobulins (Ig's). Exposure of the body to an antigen from outside the body, for example bacteria or toxins, can lead to activation of plasma cells and formation of antibodies which are responsible for destruction of 5 6 antigen. Humoral immunity is a major defense against bacterial infections. Humoral immunity can also cause immediate hypersensitivity reactions such as bronchial asthma. Cellular Immunity: is mediated by T-lymphocytes. It is responsible for delayed allergic reactions (such as eczema) and rejection of transplants of foreign tissue. The cytotoxic T cells destroy cells that have the antigen 6 7 which activated them. One mechanism by which they kill is insertion of pore-forming molecules (perforins) in the membranes of their target cells which leads to destruction of the cells by osmotic lyses. Immune system problems of clinical significance: Hypersensitivity (allergy): is an undesirable side effect of immunity. It is defined as an inappropriate activation of the body’s immune system which may result in a very strong inflammation and tissue damage. Types of hypersensitivity: 1. Immediate hypersensitivity: This is caused by B-cell immunity. There is reaction between antibodies and antigens. The symptoms appears within a few minutes of exposure to foreign antigen. For example, bronchial asthma, food allergies, hays fever. 2. Delayed hypersensitivity: mediated by T-lymphocytes and symptoms take several hours or days to develop. Examples, poison oak, eczema, soaps, measles, cosmetics, & drugs. Q: write short notes on the allergies in the allergic person. Give examples 7