Lymph nodes are very important anatomical structures. Lymph nodes can be found by careful palpation to identify these small soft structures. The palpable lymph nodes are called peripheral lymphnodes. Peripherial indicates that they are on the outside. Internal lymph nodes are present, but unless they are very large, they cannot be felt. Lymph nodes are located at points of the lymphatic system. The lymphatic system is a system of very thin walled vessels that carry lymph. Lymph is fluid that circulates through the entire body much like blood. Lymph flow is essential to life yet is one of the least understood systems of the body. Lymph fluid is composed of water, proteins (antibodies) and lymphocytes. Lymphocytes are the white blood cells responsible for producing antibodies. The lymph fluid circulates but does not have a pump like the heart for circulation. Lymph circulates by the action of muscles and takes advantage of other areas of the body such as the negative pressure of the chest cavity. When limbs do not move the lymph flow stagnates which leads to swelling. The fluid present in such swelling is usually lymph. Lymph nodes are located strategically along the lymph circulatory system. These nodes house many lymphocytes, which process antigen for antibody production. Lymphnodes become very active in the production of antibodies for a diseased organ which it receives the lymph drainage from. If you have an abscessed tooth on your left jaw, then the lymph node under that jaw will be inflamed. That is it is trying to build antibodies to fight the infection in your jaw. When we have strep throat our lymph nodes in our neck are enlarged. The lymph node will capture the draining fluid from an infected organ and process the foreign material to use to make antibodies to protect the body. Therefore, we need to learn to feel for the lymph nodes that drain various parts of the body. Enlargement of these nodes can give us an indication of disease of these regions. If a lymph node is enlarged, it can be biopsied to help determine the type of disease process that is occurring.
For example, dogs with Demodex will actually have mites present in their lymph nodes. Pets with bacterial infections will have bacteria within their lymph nodes. Dog Lymph nodes should be small, soft and non-painful. If a lymph node is hard, hot, or painful then a concern about that region of the body is developed. The common locations for the peripheral lymph nodes in dogs are the cervical nodes under the back of the jaw, the pre-scapular which are between the shoulder and the neck. The axillary lymph nodes are under the front legs and the inguinal lymph nodes are in the inguinal region of the back legs. The popliteal nodes are behind the knee. Please practice feeling for these nodes, it would be great for you to be responsible for finding a previously unknown infection or other illness. Lymph nodes are also enlarged in cancer. Leukemia is cancer of the lymphocytes and can be put in remission if caught early. Other cancers can be diagnosed by biopsy of an affected lymph node. Lymph node removal has been shown to slow the growth of cancer in an area as well. Poorly functioning lymphatics (lymph vessels) cause swelling or edema of an organ. The largest lymph vessel is called the thoracic duct and is located in the chest. Rupture of this duct occurs in dogs and cats and causes a condition called chylothorax. This is a white fluid (lymph) which floods the chest causing the animal to have severe breathing problems. Surgical ligation of the thoracic duct may be helpful. Congenital absence of the lymphatics is also possible and can occur in the intestines. The lymph in the intestines absorbs a large amount of the fat that we eat and absence of the lymphatics (lymphangiectasia) is a serious cause of diarrhea in young affected dogs (this condition is rare). W/D food is used for this disease.
White blood cells apart from some lymphocytes are produced in the bone marrow. The white blood cell act to protect the body from disease. White blood cells are the policemen of the body. Just as there are different types of policemen there are different types of white blood cells.
Neutrophils are the first on the scene when invaders are detected. When the body detects foreign invaders it sends out a chemical signal that attracts the neutrophils. The can move through the blood vessel walls to get to wherever they are needed. They contain granules which kill bacteria and viruses. The life span of a neutrophils is very short, only 8 hours.
Monocytes are circulating cells macrophages are found in the tissues. These are the Crime Scene Investigators. They inspect the scene of the crime after the neutrophils have killed something and pick up the antigens and take them back to the lymph node. They are five times as big as a neutrophil.
Like the neutrophil the eosinophil contains granules, the difference being that the granules stain red instead of purple. Allergic reactions are caused by mast cells degranulating. Eosinophils neutralize the mast cells. Their job is to fight parasites and allergies. Eosinophils live for 24 – 35 hours.
Basophils have blue staining granules. They are a second line of defense against parasites and allergies and are present in severe allergic and parasitic infections.
Only 10% of lymphocytes are in the circulation. They prefer to stay at headquarters and analyze the evidence and synthesize new antibodies to fight infection. B-lymphocytes are produced in the bone marrow. T-lymphocytes are produced in the thymus. T-lymphocytes act like smart bombs and kill specific invaders. B-lymphocytes manufacture antibodies. Lymphocytes are very long lived and are capable of division or transforming into more active forms in the lymph node.
Lymph nodes act as police headquarters collecting the evidence (antigens) from the macrophages and producing antibodies to fight disease.