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Slide 2:

At the end of the session the students should be able to a ) List the lymphoid tissues in the body b) Describe the significance of lymphoid tissues c) Discuss the formation flow and functions of lymph d) Classify immune system of the body e) Discuss the natural and acquired immune system

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* It represents the difference between the filtered and the reabsorbed fluids across the capillary membrane. * Normally, lymph flow rate is: 120 ml./hour (i.e., 2-4 L/day) during rest. Lymphatic Circulation Definition: Lymph is the fluid that returns to the blood stream from tissue spaces by lymphatic vessels. Rate of lymph flow:

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Thoracic duct Right lymphatic duct * drains lymph from: lower limbs – abdomen – left half of thorax – left side of head and neck – left upper limb. * lymph flow rate: 100 ml./hour. * drains in the left subclavian. * drains lymph from: right half of thorax – right side of head and neck – right upper limb.   * lymph flow rate: 20 ml./hour. * drains in the right subclavian . lymphatic capillaries which unit together large lymphatic vessels ( have unidirectional valves) 2 lymphatic ducts: Lymph is drained by lymphatic system : 1- Almost all the body have lymphatic drainage except: CNS - deep parts of nerves – superficial parts of the skin – bone marrow,cornnea,inner ear. 2- Lymphatic system is formed of:

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Lymph is a part of the interstitial fluid (I.S.F.) characterized by the following: Physical: - colourless . – isotonic. - pH 7.4. - transparent except during fat absorption where It looks milky due to fat globules. Chemical : It is similar to plasma except in: * Less proteins (average 2 gm %) but protein concentration varies according to the site of drainage form 0-6 gm % . * A/G ratio is greater in lymph than in plasma because albumin has smaller molecular weight. * Less number of lymphocytes than plasma. * Less amount of fibrinogen, prothrombin , Ca ++ and no platelets, so it clots but slower than plasma . Composition of lymph:

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1. Drainage of excess I.S.F. from capillaries back to the blood --> prevent accumulation of fluid and edema. This also maintains blood volume. 2. Removal of substances having large molecular weight (proteins and metabolites), because lymphatic capillaries are more permeable than blood capillaries. The amount of proteins returns to blood by lymph is 25 - 50% of total circulating plasma proteins, so lymph flow maintains plasma proteins. 3. Absorption of fat and fat - soluble vitamins from the intestine. 4. Lymph nodes functions are: - formation of lymphocytes. - removal of bacteria (protective mechanism). Functions of lymphatic system:

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Immune organs

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Immune defenses can be classified into 2 types which usually interacts: Nonspecific immune defenses (Innate Immunity) Protect against microbes or F.B. (invaders) without having to recognize their specific identity. The mechanisms used are not specific to any invader. Specific immune defenses (Acquired Immunity) Protect against microbes to which the body is previously exposed (recognized before) either through infection or immunization. The mechanisms used are specific for each invader.

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Acquired Immunity Innate Immunity Specific i.e., Reacts to a specific invader each time and can not react to another. Non-specific i.e., Reacts to invaders from different type Specificity Very high i.e., Although the cells are of the same type, each group shows totally different surface molecules. Limited Diversity Yes Remembers the invader on re-exposure. No Memory Yes Yes Non-reaction to self Components Lymphocytes Phagocytes & natural killer cells Cells Antibodies Complement Molecules

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Mechanisms of Innate Immunity I - Defenses at Body Surfaces Very few microorganisms can penetrate the intact skin, Various skin glands & tears contain anti-microbial agents Mucus secreted by epithelial lining contain antimicrobial agents and sticky to which microbes adhere. Hairs at the entrance of nose Cough and sneezing reflex Acid secretion by the stomach and uterus

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II- Inflammation 1. Initial entry of bacteria into tissue 2. Vasodilation in the infected area, leading to increased blood flow 3. Marked increase in protein permeability of the capillaries and venules in the infected area, with resulting diffusion of protein and filtration of fluid into the interstitial fluid. 4. Chemotaxis : exit of leukocytes from the venules into the interstitial fluid of the infected area 5. Destruction of bacteria in the tissue either through phagocytosis or by mechanisms not requiring phagocytosis. 6. Tissue repair

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family of plasma proteins which is involved in: killing of microbes without prior phagocytosis. Opsonization : making phagocytosis easier. Chemotaxis : Direction of phagocytes toward the source of infection. III- Complement opsonization

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IV- Interferons are a family of cytokines that nonspecifically inhibit viral replication inside host cells

Antigen (immune stimulant) :

Antigen (immune stimulant) Is any foreign substance which when introduced into the body ,is capable to stimulates specific immune response. Antigen nature: either proteins or high molecular weight polysaccharides (8000 or greater) that are specific for each type organism.

Basic types of acquired immunity :

Basic types of acquired immunity 2) Cell-mediated immunity = T cell immunity 1) Humoral immunity = B cell immunity Performed by T-lymphocyte s It's a major defense against viral & fungal infection The T-cell them selves can kill the abnormal cells. It is also responsible for allergic reactions and rejection of transplanted organs. Performed by B-lymphocytes It's a major defense against bacterial infection The B-lymphocytes produce antibodies that kill bacteria

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Acquired Immunity involves the following steps: 1) Antigen recognition and presentation by “antigen presenting cells” . 2) Lymphocyte activation and differentiation. 3) Elimination of antigen by: Antibodies secreted by plasma cells (differentiated from B-lymphocytes). Direct attack by activated T- cytotoxic cells.

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Functions of different types of T-lymphocytes 1) Helper T-lymphocytes (TH cells): - They are the most numerous of the T-cells (75%). - They serve as the major regulator of all immune functions. They do this by forming a series of protein mediators, called lymphokines , that act on other cells of the immune system as well as on the bone marrow cells. 2) Cytotoxic -T cells ( Tc ) or killer cells - Tc is a direct attack cell that is capable of killing micro-organisms and some of the body’s own cells specially when they are cancerous or invaded with viruses. They are also responsible for rejection of transplants of foreign tissues. 3) Suppressor T-lymphocytes (Ts cells) -Ts cells are capable of suppressing the functions of both cytotoxic and helper T cells.



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