Thymus
Bilobed organ located in the mediastinum b/t the sternum and the aorta Immature T cells migrate from the red bone marrow to mature. Mature T cells leave the thymus, enter the blood stream and migrate to lymph nodes, the spleen, and other lymphatic tissue. foals: thymus is large Maturity: thymus atrophies and the secondary lymphatic organs are populated with mature T cells. Some T cells continue to mature in the thymus throughout a lifetime.
Lymph Nodes
Lymph nodes are firm, smooth surfaced, oval or bean shaped structures Some are superficial in location and can be identified through palpation. Each node is bound by a capsule Located along lymphatic vessels ~ 8000 bean-shaped lymph nodes Usually occur in groups lymphocentres Lymph nodes function as a type of filter Lymph flows through a node in one direction only
Lymph enters through afferent lymphatic vessels which penetrate the node at several locations. The afferent vessels contain one-way valves opening toward the center of the node. foreign substances are trapped by reticular fibres within the sinuses of the node. Macrophages then destroy some foreign substances by phagocytosis while lymphocytes destroy others by immune responses. Filtered lymph then leaves through one or two efferent lymphatic vessels containing valves opening away from the node.
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