Lymph nodes are unique organs of mammals. Normal people's superficial lymph nodes are very small, mostly within 0.5 cm in diameter, with smooth and soft surface, no adhesion with surrounding tissues and no tenderness. When bacteria enter your body from the wound, lymphocytes will produce lymphatic factor and antibodies, effectively killing bacteria. The result is reactive proliferation of lymphocytes and histiocytes in lymph nodes, which makes lymph nodes swollen, which is called reactive proliferation of lymph nodes. Viruses, certain chemicals, toxic products of metabolism, denatured tissue components and foreign bodies can also cause reactive hyperplasia of lymph nodes. Therefore, swollen lymph nodes are a beacon of the human body and an alarm device.

Peripheral lymphoid organs peculiar to mammals are composed of lymphocytes. Bean-shaped, located on the way of lymphatic vessels, is one of the important organs that produce immune response. One side of the lymph node is convex, connecting several input lymphatic vessels, and the other side is concave, called "gate", with output lymphatic vessels and nerves and blood vessels entering and leaving. The surface of lymph nodes is covered with tunica, and the connective tissue of tunica extends into lymph nodes to form trabecula, which constitutes the scaffold of lymph nodes. Below the capsule is the cortical area. The center and hilum of lymph nodes are medullary regions. There are lymphoid nodules, diffuse lymphoid tissue and cortical lymphatic sinus (dermal sinus for short) in cortical area. Medulla includes dense lymphoid tissue composed of medullary cord and medullary sinus (medullary sinus for short). There are many lymphocytes and macrophages in the sinus cavity of lymphatic sinus. Lymph from the afferent lymphatic vessels first enters the dermal sinus, then flows to the medullary sinus, and finally leaves the lymph nodes through the efferent lymphatic vessels. The main function of lymph nodes is to filter lymph, produce lymphocytes and plasma cells, and participate in the immune response of the body. Lymph node enlargement or pain usually indicates inflammation or other lesions in the organs in the area. Therefore, it is of great significance to examine lymph nodes according to their distribution law for diagnosing and understanding the development of some infectious diseases. Lymph nodes can't effectively filter viruses.

Lymph nodes are all over the body, and only superficial parts can be touched. The neck, jaw, supraclavicular fossa, armpit and groin are the easiest to touch. When lymph nodes are swollen, round, oval or cord-like nodules can be felt under the skin. If swollen lymph nodes are felt under the jaw, it means that there are lesions in the mouth. Such as tonsillitis and periodontitis. When there is a diseased spherical protuberance in the neck, the cervical lymph node nucleus should be considered first. Patients with nasopharyngeal carcinoma often feel cervical lymph node enlargement. Axillary lymph node enlargement,

Diseases of the upper limbs or breasts are often found. Inguinal lymphadenopathy is a signal of infectious diseases of lower limbs and buttocks. In addition, people are reminded not to ignore the pathological reactions caused by uterine cancer, testicular cancer and rectal cancer. The left supraclavicular lymph node is enlarged, which mostly indicates that there are cancer cells in the abdominal cavity that metastasize along the thoracic duct. Such as liver cancer, stomach cancer and colon cancer. The right supraclavicular lymph node is enlarged, indicating that cancer cells in the chest have metastasized upward along the right lymphatic vessel. Such as lung cancer and esophageal cancer. When suffering from lymphoblastic leukemia, the lymph nodes of the whole body are enlarged.