In the tract of lymphatics, there are small mass of tissues (from one to 25 milimeter long) in the shape of seeds of bean like the beads stringed in a thread which are called lymph nodes. These nodes are found mainly in the neck, armpit, chest, abdomen and hip joints in large number whereas in the elbow and at the back side of the knee joint in less number. Superficial lymph nodes are located near the skin in the neck, armpit and hip joints and deep nodes are found into the depth of hip joint region, near by the lumbar of vertebrae, on the base of lungs, in the mesentery near by the small intestines and in the liver. Most of lymph passes through at least one lymph node for reaching back into the blood circulation.
Lymph nodes are mantled by a capsule of fibrous connecting tissue from all around. Cilia of connecting tissues which are called trabeculae emerge inwardly towards the center of lymph node from the capsule of which node gets divided into several compartments. External portion of each part is called cortex of lymph node in which lymphocytes are present in the thick bunches which are called lymph nodules. There is germinal center at the middle of each nodule where lymphocytes originate because of cell partition. Lymph nodes produce ten billion lymphocytes in a day. Internal portion of the lymph node is called medulla in which string shaped structure of lymphocytes come out from the medullary cords nodule which make a loose spongy reticula web by hugging to each other.
There are four or five afferent lymph vessels which bring lymph into each lymph node and enter into cortical sinus by passing through the edge of convex capsule rather than cell free region and then leave their lymph. The lymph is filtered slowly by passing through the sinuses and efferent lymph vessels reach into the lymphatic ducts by brining lymph after passing through the concave edge of capsule which is called hilum.
- Lymph nodes do the work of filter. The lymph arrived in these lymph gets filtered whereby these checks to the external harmful substances and micro organism.
- Lymphocytes especially b-lymphocytes originate in the lymph nodes and macrophages are present in it and disease producing viruses get destroyed by the antibodies and antitoxins produced because macrophages. Thus, lymph nodes check the infection to spread in other portions of the body by checking the viruses from going into the blood or by destroying them.
- Lymph nodes make new lymphocytes for circulation.