Structure and Function of the Lymphatic System in Dogs
What Are the Functions of the Lymphatic System in Dogs?
The lymphatic system has several very important functions: absorbing excess fluid from tissues and returning it to the bloodstream, absorbing fat from the gastrointestinal tract, transporting white blood cells and certain proteins, and playing an important role in the immune system, particularly in the production of antibodies (immunoglobulins). The lymphatic system filters and removes debris from the tissues of the body. Cells produce proteins and waste products. The lymph absorbs these products and carries them away from the tissues because they are often too large to be effectively absorbed and removed by the bloodstream. The lymphatic system, functioning along with the circulatory system, absorbs nutrients from the small intestines. A large portion of digested fats is absorbed via the lymphatic capillaries. Fat absorbed from the small intestinal lymphatic capillaries or lacteals is termed chyle. The lymph nodes filter out cellular waste products and foreign material in the lymph fluid, including potentially dangerous infectious particles like bacteria and viruses. They trap material received from the lymphatic vessels and provide a site for white blood cells to mount an immune response. They act as a barrier against the entrance of these foreign substances into the bloodstream. The chief function of the bone marrow is the production of various red and white blood cells. The spleen is an integral part of the immune system and it filters abnormal cells from the blood. It also helps make and store blood cells. The thymus is a very important part of the immune system in the newborn. It is the site where the earliest immune cells are made and where immune functions take place in the young animal. GALT’s main function is to provide immunologic defenses at the surface of certain areas of the body, such as the tonsil and the lining of the intestinal tract. These are areas where the body is often exposed to foreign materials and infectious agents.
What Are Common Diseases of the Canine Lymphatic System?
Due to the distribution and complexity of the lymphatic system, many disorders may affect all or some part of it. The most common disorders seen in dogs include the following: Lymphoma or lymphosarcoma is a tumor of white blood cells. It is a malignant cancer, and it may affect one or more parts of the lymphatic system. Lymphoma may occur as a solid tumor associated with the lymph nodes, the intestines, kidneys, liver, spleen, thymus or other parts of the body. It may also develop as a circulating form that is confined largely to the bone marrow and blood stream. Lymphoma is one of the most common cancers seen in dogs, and has been treated with chemotherapy protocols for a number of years. Lymphadenopathy is enlargement of the lymph nodes. It may represent lymphosarcoma, but may also develop for other reasons. Lymph nodes may enlarge when they are reacting to foreign substances or infection. They become larger as white blood cells proliferate within the nodes. Such reactions may also occur following vaccination or with any chronic inflammation within the body. Lymphadenitis is inflammation of the lymph nodes. It may involve one or several lymph nodes, depending upon the cause. Common causes include wounds, skin infections, infections within the soft tissues of the body, nonlymphatic tumors, and areas of active healing. Chylothorax is the accumulation of chyle in the chest cavity from rupture, obstruction, or abnormal development of the thoracic duct. It may develop secondary to heart disease, tumors of the thorax, diaphragmatic hernias, trauma, fungal infections, heartworm disease, and for unknown reasons. It is more common in Afghan hounds and Shiba Inu dogs than in other breeds. Lymphangitis is an inflammation of the lymph vessel. It often arises from trauma, foreign bodies, and infections. It may occur at the same time as lymphadenitis. Lymphangiectasia is an obstructive (blockage) disorder that causes dilation of the lymph vessels, particularly in the intestinal tract. Lymphedema is an accumulation of lymph in the soft tissues of one or more of the limbs. Congenital forms occur in some dogs (e.g. poodles, Labrador retriever, Great Dane) due to deformities in either the lymphatic channels or the lymph nodes themselves. Acquired forms may occur with blockage or destruction of lymph vessels from trauma, surgery, inflammation, infection, tumors, or radiation therapy. In some cases the soft tissue swells so much that the limb may be painful or dysfunctional.
What Types of Diagnostic Tests Are Used to Evaluate the Lymphatic System in Dogs?