The Lymphatic System

A key component of the immune system is the lymphatic system. The lymphatic system can be thought of as a secondary circulatory system. The lymph vessels contain a clear, colorless fluid called lymph, which is derived from a network of capillaries which collect this clear fluid as it filters through the capillaries of the blood. The lymphatic system provides our immune defenses, filters foreign substances and cell debris from the blood and destroys them; and produces a type of white blood cells known as lymphocytes, which circulate in the blood and lymph vessels.

Lymph passes from tiny capillaries to lymph vessels and flows through lymph nodes that are located along the course of these vessels. Cells of the lymph nodes phagocytize, or ingest, such impurities as bacteria, old red blood cells, and toxic and cellular waste. Finally, the lymph flows into either the thoracic duct, a large vessel that runs parallel to the spinal column, or into the right lymphatic duct, both of which transport the lymph back into veins of the shoulder areas where is reenters the general circulation. All lymph vessels contain one-way valves, like the veins, to prevent backflow.

In an infection, the lymph nodes occasionally become enlarged with lymph and white blood cells and become palpable (can be felt by an examiner). These can be felt most easily at the neck, in infections of the neck and head; in the axillary region (the armpit), in infections of the breast or arm; and in the inguinal region (the groin), in infections of the pelvis or lower extremities.

Unlike the blood, which is forced through the arteries by the pumping action of the heart, the flow of lymph is not aided by a pump. The lymph moves by way of the one-way valves, aided by the compression of lymph vessels when the muscles of the body contract. Therefore, exercise and activity is very important for the proper circulation of the lymphatic fluid.

The tissues of the lymphatic system include the spleen, thymus, bone marrow, and aggregates of lymphatic tissue located in the tonsils and intestines (including the appendix). The spleen, thymus, and bone marrow manufacture lymphocytes, which are the major cell type of the system. The spleen is also involved in the destruction of old cells and other substances by phagocytosis and plays a role in immune responses. The thymus is considered the central organ that controls lymphocyte production and antibody formation.

Lymphatic tissues of the intestines are known as lacteals. They absorb digested fat (lipids), which are transported by the veins to the liver where they are processed for use by the body. Lymph fluid from lacteals is milky white because of the fat globules that are present.

The most common cell of the lymphatic system is the lymphocyte. Lymphocytes can be classified as T cells (thymus-derived) or B cells (bone-marrow-derived). Other cells of the lymphatic system include histiocytes, which are responsible for structural support of lymph tissue and for phagocytosis; monocytes, which also function to ingest foreign substances; and plasma cells, which synthesize and release antibodies. Monocytes are believed to originate from lymphocytes. 

Lymphadenitis

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Lymphadenitis is an infection of the lymph nodes (also called lymph glands). It is a common complication of certain bacterial infections.

Causes

The lymph system is a network of lymph nodes, lymph ducts, lymph vessels, and organs that produce and move a fluid called lymph from tissues to the bloodstream. For more information on this part of the body, see lymph system.

The lymph glands, or nodes, are small structures that filter the lymph fluid. There are many white blood cells in the lymph nodes to help fight infection.

Lymphadenitis occurs when the glands become enlarged by swelling (inflammation), usually in response to bacteria, viruses, or fungi. The swollen glands are usually found near the site of an infection, tumor, or inflammation.

Lymphadenitis may occur after skin infections or other infections caused by bacteria such as streptococcus or staphylococcus. Sometimes it is caused by rare infections such as tuberculosis or cat scratch disease (Bartonella).

Symptoms

• Red, tender skin over lymph node
• Swollen, tender, or hard lymph nodes

Lymph nodes may feel rubbery if an abscess has formed.

The health care provider will perform a physical exam, which includes feeling your lymph nodes and looking for signs of injury or infection around any swollen lymph nodes.

A biopsy and culture of the affected area or node may reveal the cause of the inflammation. Blood cultures may reveal spread of infection to the bloodstream.

Lymphoma

Lymphoma is a cancer of a part of the immune system called the lymphatic system. There are many types of lymphoma. One type is called Hodgkin disease. The rest are called non-Hodgkin lymphoma.

Non-Hodgkin lymphomas begin when a type of white blood cell, called a T cell or B cell, becomes abnormal. The cell divides again and again, making more and more abnormal cells. These abnormal cells can spread to almost any other part of the body. Most of the time, doctors can't determine why a person gets non-Hodgkin lymphoma.

Non-Hodgkin lymphoma can cause many symptoms, such as

    Swollen, painless lymph nodes in the neck, armpits or groin
    Unexplained weight loss
    Fever
    Soaking night sweats
    Coughing, trouble breathing or chest pain
    Weakness and tiredness that don't go away
    Pain, swelling or a feeling of fullness in the abdomen