|
A lymph node is an oval-shaped organ of the lymphatic system, distributed widely throughout the body including the armpit and stomach and linked by lymphatic vessels. Lymph nodes are major sites of B, T, and other immune cells. Lymph nodes are important for the proper functioning of the immune system, acting as filters for foreign particles and cancer cells. Lymph nodes do not deal with toxicity, which is primarily dealt with by the liver and kidneys. Lymph nodes also have clinical significance. They become inflamed or enlarged in various infections and diseases which may range from trivial throat infections, to life-threatening cancers. The condition of the lymph nodes is very important in cancer staging, which decides the treatment to be used, and determines the prognosis. When swollen, inflamed or enlarged, lymph nodes can be hard, firm or tender. ==Structure== Lymph nodes are bean or oval shaped and range in size from a few millimeters to about 1–2 cm long.〔 Each lymph node is surrounded by a fibrous capsule, and inside the lymph node the fibrous capsule extends to form trabeculae. The substance of the lymph node is divided into the outer cortex and the inner medulla. The cortex is continuous around the medulla except at the hilum, where the medulla comes in direct contact with the hilum. Thin reticular fibers and elastin form a supporting meshwork called a ''reticular network'' inside the node. White blood cells (leukocytes), the most prominent ones being lymphocytes, are tightly packed in the follicles (B cells) and the cortex (T cells). Elsewhere in the node, there are only occasional leucocytes. As part of the reticular network there are follicular dendritic cells in the B cell follicle and fibroblastic reticular cells in the T cell cortex. The reticular network not only provides the structural support, but also the surface for adhesion of the dendritic cells, macrophages and lymphocytes. It allows exchange of material with blood through the high endothelial venules and provides the growth and regulatory factors necessary for activation and maturation of immune cells. The number and composition of follicles can change especially when challenged by an antigen, when they develop a germinal center.〔 Lymph enters the convex side of the lymph node through multiple afferent lymphatic vessels, to flow through the sinuses. A lymph sinus which includes the subcapsular sinus, is a channel within the node, lined by endothelial cells along with fibroblastic reticular cells and this allows for the smooth flow of lymph through them.The endothelium of the subcapsular sinus is continuous with that of the afferent lymph vessel and is also with that of the similar sinuses flanking the trabeculae and within the cortex. All of these sinuses drain the filtered lymphatic fluid into the medullary sinuses, from where the lymph flows into the efferent lymph vessels to exit the node at the hilum on the concave side.〔 These vessels are smaller and don't allow the passage of the macrophages so that they remain contained to function within the lymph node. In the course of the lymph, lymphocytes may be activated as part of the adaptive immune response. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「lymph node」の詳細全文を読む スポンサード リンク
|