Lymphatic system and Lymphoid Organs.pdf

Lymphatic system and Lymphoid Organs 1 Classificauon of lymphoid organs Primary lymphoid organs and structures : - Bone marrow. Site of origin of T and B lymphocytes. B lympho-cytes directly seed secondary lymphoid rstructures ii and organs. -...

Lymphatic system and Lymphoid Organs 1 Classificauon of lymphoid organs Primary lymphoid organs and structures : - Bone marrow. Site of origin of T and B lymphocytes. B lympho-cytes directly seed secondary lymphoid rstructures ii and organs. - Thymus. T lymphocytes from bone marrow undergo further maturation in the thymus before seeding secondary lymphoid structures and organs. Secondary lymphoid organs and structures: ww Diffuse lymphoid tissue in Lymphoid nodules. Both solitary and in aggregates. we Tonsils, lymph nodes and spleen Mucosa-Associated Lymphoid Tissue (MALT) - Located in the lamina propria of the respiratory and digestive systems. is - Composed of clusters of lymphocytes and other cells capable of responding to antigens. - Filters and provides immune surveillance for tissue fluid in the lamina propria. Lymph Vessels - Lymph vessels are fine tubes that contain lymph. - They assist the cardiovascular system in removing tissue fluid from body spaces and returning it to the blood. - Found in all tissues and organs except the CNS, eyeball, internal ear, epidermis, cartilage, and bone marrow. Functions of Lymphoid Tissue The lymphoid organs: - Provide immune surveillance and defense against foreign substances and microorganisms. - Provide immune tolerance, distinguishing between "self" and "non-self." I - Absorb lipids into small lymphoid vessels (lacteals) in intestinal villi for distribution to the bloodstream. - Help maintain fluid balance by accumulating tissue fluid and white blood cells in lymph vessels and returning them to the blood. Circulation of Lymph - Lymph capillaries are a network of fine vessels that drain lymph from tissues. - They have a similar structure to blood capillaries but are wider and less regular. - Small lymph vessels drain this capillary plexus and unite to form larger lymph vessels, which converge on primary lymph nodes. - The lymph passes through these nodes and leaves in vessels that usually converge on secondary and tertiary lymph nodes. sina. m Lymphatic Vessels - Lymph drains through a number of lymph nodes and is gathered into larger lymph vessels before returning to the bloodstream via great veins at the root of the neck. 5 - Lymph vessels have numerous valves. The vessels that carry lymph an to a node are called afferent vessels, and those that carry it away are efferent lymph vessels. i Tonsils fi - Pharyngeal, lingual, and palatine tonsils are located at the junction of the oral cavity with the pharynx. - Composed of aggregations of lymphoid nodules and diffuse lymphoid tissue.  Thymus d - A primary lymphoid organ that receives immature lymphocytes (thymocytes) from the bone marrow. - These cells mature in the thymus and are carried to secondary lymphoid structures byvia the blood vascular system. - A connective tissue capsule surrounds the thymus and extends into it, dividing it into lobules. bies www.iw Thymus Structure - Each lobule contains: - An outer cortex densely packed with thymocytes (developing T lymphocytes). - An inner medulla with fewer thymocytes. - A blood-thymic barrier around capillaries in the cortex to protect developing lymphocytes from circulating antigens. Diffuse Lymphatic Tissue I - Located in the lamina propria of any organ opening to the exterior of the body. - Composed of clusters of lymphocytes and other cells capable of responding to antigens. - Diffuse lymphatic tissue is also located in tonsils, lymph, nodes, and spleen. Lymph Nodules - Found in the lamina propria of any organ opening to the exterior. - May occur singly (solitary) or in clusters (aggregates) such e as in tonsils and Peyer's patches in the small intestine. - Primary nodules are present before antigen stimulation. consists primarily of densely packed B lymphocytes. - secondary nodules appear after stimulation. central pale core, the germinal center, appears i This center is composed of immunoblasts that divide to form lymphocytes that accumulate inthe densely packed, peripheral zone of the nodule.