Ch 23 Lymphatic System.docx

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Biological Sciences
BIO 121
Jason Ramsay

Ch 23 Lymphatic System The lymphoid system consists of: - Lymph - Lymphatic vessels - Lymph nodes - Lymphoid organs (spleen) Lymph consists of: - Interstitial fluid - Lymphocytes - Macrophages Primary lymphoid structure - Causes differentiation of lymphocytes resulting in: o T cells, B cells, and NK cells Secondary lymphoid structure (lymph nodes and tonsils) (most immune responses originate here) - Consists of lymphocytes and more B cells to battle infectious agents Functions of the Lymphoid System  Produces and distributes lymphocytes  Maintains normal blood volume  Maintains chemical composition of interstitial fluid  Provides an alternative route for the transport of: o Hormones o Nutrients o Waste products Lymphatic Capillaries - Comparisons to the vascular capillaries: o Lymphatic capillaries are larger in diameter o Lymphatic capillaries have thinner walls o Lymphatic capillaries have an irregular outline - Comparisons to the vascular capillaries o Lymphatic capillaries have anchoring filaments that connect to the surrounding connective tissue to keep the capillaries open o Lymphatic capillaries have greater permeability Comparisons of lymphatic vessels to veins  Lymphatic vessels have thinner walls  Lymphatic vessels have larger lumens  Lymphatic vessels do not have easily identifiable tunics (layers)  Larger lymphatic vessels have valves just like most veins have Lymph Movement - Valves of Lymphatic Vessels o Pressure in the lymphatic vessels is lower than the pressure in the veins o Valves prevent the backflow of lymph o Skeletal muscles contract to help propel lymph o Inhalation decreases thoracic pressure, which helps to move lymph toward the venous system (subclavians) The thoracic duct collects lymph from tissues inferior to the diaphragm and from the left side of the upper body. The right lymphatic duct drains the right half of the body superior to the diaphragm. Lymphocytes  Lymphocytes (white blood cells) are the primary cells of the lymphoid system, and they are responsible for specific immunity.  They respond to the presence of: o Invading organisms, such as bacteria and viruses o Abnormal body cells, such as virus-infected cells or cancer cells o Foreign proteins, such as the toxins released by some bacteria  Three different classes of lymphocytes o T cells (Thymus dependent) 80%  Cytotoxic T cells (Attack foreign cells or infected cells)  Helper T cells (control activation and activity of B cells)  Suppressor T cells (control activation and activity of B cells)  Memory T
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