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c22 - Anatomy and Physiology Lecture Biology 2402 CHAPTER...

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Anatomy and Physiology Lecture Biology 2402 CHAPTER 22 THE LYMPHATIC SYSTEM AND IMMUNITY
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THE LYMPHATIC SYSTEM AND IMMUNITY Pathogens are disease-producing organisms. Survival and good health depends on fending off attacks of pathogen. Resistance is the ability to ward off diseases through our defenses. Susceptibility is vulnerability or lack of resistance. Resistance grouped in two broad areas : (1) Nonspecific resistance - Includes defense mechanism that provide general protection against invasion by a wide range pathogens, such as the many different kinds of bacteria and viruses. These include: (a) Mechanical barriers provided by the skin and mucus membranes; (b) Antimicrobial chemicals; (c) Phagocytosis; (d) Inflammation; and (e) Fever (Example: The acidity of the stomach contents kills many bacteria ingested in food). (2) Immunity - Involves activation of specific lymphocytes that combat a particular pathogen or other foreign substance. Specific resistance. The body system that carries out immune response is the lymphatic system .
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Lymphatic System - Consist of: 1) Liquid called lymph 2) Lymphatic vessels (lymphatics) - that transport lymph 3) Structures and organs that contain lymphatic (lymphoid) tissue 4) Bone marrow which houses stem cells that develop into lymphocytes. Interstitial (tissue) fluid and Lymph are basically the same. The major difference between the two is location. Fliud from interstitial tissue becomes lymph after it passes from interstitial space to lymphatic vessels. Lymphatic tissue is a specialized form of reticular connective tissue (blood) that contains large number of lymphocytes. FUNCTIONS OF THE LYMPHATIC SYSTEM 1. Fluid Balance - Lymphatic vessels drain tissue spaces of excess interstitial fluid. 2. Fat absorption - Lymphatic system absorbs fats and other substances from the digestive tract. Fats enter the lacteals (special lymphatic vessels located in the small intestine) and pass through the lymphatic vessels to the venous circulation. 3. Defense – Microorganisms and other foreign substances are filtered from lymph by lymph nodes and from blood by the spleen. Lymphocytes (A type of white blood cell found in lymph nodes), aided by macrophages (phagocytic cell derived from a monocyte), recognize foreign cells and substances, microbes, and cancer cells. R espond to foreign cells in two basic ways:
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1. Some lymphocytes ( T cells ) destroy the intruders directly (by causing them to rupture) or indirectly by releasing cytotoxic (cell-killing) substances. 2. Other lymphocytes ( B cells ) differentiate into plasma cells that secrete antibodies. These are proteins that combine with and cause destruction of specific foreign substances. LYMPHATIC VESSELS AND LYMPH CIRCULATION Lymphatic Vessels begin as closed-ended vessel called lymphatic capillaries in spaces between cells.
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