Ch 20 & 21 Lymphatic System and Immunity

Ch 20 & 21 Lymphatic System and Immunity - Ch 20...

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Ch. 20: The Lymphatic System Overview Anatomical organization: 3 components o Lymphatic vessels originate in periphery, drain into veins o Lymph fluid w/in lymphatic vessels; similar to plasma but lower [protein] o Lymphoid organs & tissues contain lymphocytes connected to lymphatic vessls Functions: 3 primary tasks o Production and distribution of lymphocytes o Return of fluids and solutes from peripheral tissues to blood Aids in maintenance of blood volume and blood pressure Stabilizes composition of interstitial fluid o Absorption of digested fat from the gut Lymphatic vessels Lymphatic capillaries Smallest lymphatic vessels Originate as blind-ended pockets in peripheral tissue Differ structurally from cardiovascular capillaries in the following ways: Lger diameter Thinner walls =>leaky = less selectively permeable lge proteins, viruses, bacteria excluded from blood can enter lymph due to endothelium but basement membrane incomplete endothelial cells not held together, just overlapped =>overlap creates one-way door, prevents outflow Smaller lymphatic vessels Resemble small and medium veins Collect lymph from lymphatic capillaries Have internal valves, like veins, to prevent backflow Major lymph-collecting vessels 2 sets: Superficial lymphatics drain the skin and mmbs of body cavities Deep lymphatics drain organs =>larger than superficial lymphatics =>run alongside deep arteries & veins Both sets converge to form the largest lymphatic vessels: Thoracic duct =>collects from ¾ body: all lower, upper left quadrant =>begins at cisterna chyli =>drains into left subclavian vein, near left internal jugular Right lymphatic duct =>collects from upper right quadrant =>drains into right subclavian vein Blockage of lymphatic vessels prevents collection of excess extravasated fluid and results in the accumulation of fluid in interstitial spaces around organs and tissues = EDEMA
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Types of Lymphocytes Lymphocytes are agranular leukocytes (white blood cells, or WBCs) Circulating lymphocytes make up ~30% of total circulating WBCs =>most lymphocytes are not in circulation, they in lymphoid organs 3 classes of lymphocytes: T-cells B-cells NK (natural killer) cells All lymphocytes are formed in bone marrow. T-cells (80% circulating lymphocytes) During maturation of the immune system, some lymphocytes migrate out of bone marrow to the thymus (a lymphoid organ), come under the influence of thymic hormones and become T-cells. The “T” stands for thymus-dependent . Subtypes of T-cells : Cytotoxic T-cells (T c ) Responsible for cell-mediated(cellular) immunity Attack foreign or infected cells directly and kill them Helper T-cells (T H ) Coordinate activation of both cytotoxic T-cells and B cells = Regulatory T-cells Suppressor T-cells (T s ) Coordinate inhibition of both cytotoxic T-cells and B cells = Regulatory T-cells B-cells (10-15% circulating lymphocytes) During maturation of the immune system, B cells remain in bone marrow and are influenced by hormones present there. The “B” stands for bone-marrow derived .
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