Lymphatic System

Lymphatic System

Reviewed By:
Mark Oren, M.D., FACP


The lymphatic system consists of various glands, organs and ducts connected throughout the body. It removes lymph (fluid containing white blood cells, plasma and other substances) from the tissues and returns it to the bloodstream. The lymphatic system is an important part of the immune defense system. In addition to extracting lymph fluid from tissues, the lymphatic system produces and stores some of the cells needed by the body to fight infections and diseases, including cancer.  

Lymph is transported throughout the body in tubes known as lymph vessels. Without lymph vessels, the lymph fluid would collect in the tissues and cause swelling. Located along the lymph vessels are lymph nodes (small, bean-shaped organs clustered in various areas of the body). Their functions include producing immune cells to fight infection and filter bacteria and other foreign material from lymph. 

In addition to the lymph fluid, lymph vessels and lymph nodes, the lymphatic system also involves a number of organs and tissues, including:

  • Spleen. An organ involved in the detruction of worn-out or damaged red blood cells and platelets and in the production of certain white blood cells.

  • Thymus. An organ responsible for developing T lymphocytes (T cells) during fetal development.

  • Bone marrow. The soft inner part of bone in which all forms of blood cells are produced.

  • Adenoids and tonsils. Masses of tissue that produce antibodies against antigens or threats to the body, such as germs, mismatched red blood cells and cancer cells.

The lymphatic system is closely linked to cancer. It is an important factor in the body’s response against cancer, and is also one of the most common pathways for the spread of cancer cells to other areas of the body (metastasis).

Cancer of the lymphatic system is known as lymphoma. In addition to this group of diseases, a variety of other cancers may also develop in areas of the lymphatic system. These diseases include:

  • Thymus cancer
  • Multiple myeloma (bone marrow)
  • Leukemia (bone marrow)
  • Tonsillar cancer
  • Adenoidal cancer

Cancers that do not start in the lymph system, such as breast cancer, can spread or metastasize to the lymph system easily. After the cancer cells are in the lymph system, it is much harder to contain the cancer, significantly affecting the patient’s prognosis for recovery.

About the lymphatic system

The lymphatic system consists of organs, nodes and vessels that are responsible for draining a fluid called lymph and returning it to the bloodstream. Lymph is composed of plasma, white blood cells and other substances.

Lymph fluid continually flows out of the thin walls of the capillaries into surrounding body tissues, where its proteins, minerals and nutrients provide nourishment to the tissues.  

Although most of the lymph is reabsorbed into the capillaries, some of the lymph remains in the spaces surrounding the cells. The lymph vessels are a network of tubes or canals that branch off into tissues throughout the body. They collect the excess lymph from the tissues and carry it back to the blood. Without this process, the excess lymph would remain in the body tissues and cause swelling. Lymph vessels also remove and transport damaged cells, bacteria, cancer cells and other foreign material that may have entered the tissue fluids.

A major component of the immune system, the lymphatic system defends the body from foreign material by producing and storing some of the cells needed to fight infections and disease. The system includes lymph nodes, small, bean-shaped organs that are clustered in various areas of the body, including the neck, armpit, chest and groin. The lymph nodes are located along the lymph vessels and their functions include producing immune cells (e.g., lymphocytes, monocytes and plasma cells) and filtering foreign materials from lymph.  When the lymph nodes recognize antigens or other foreign material in the lymph fluid, they respond by enlarging and producing additional lymphocytes and plasma cells to help combat infection.

In addition to the lymph fluid, lymph vessels and lymph nodes, the lymphatic system also involves a number of organs and tissue masses, including:

  • Spleen.  An organ located under the rib cage on the left side of the abdomen. It is involved in the destruction of worn-out or damaged red blood cells and platelets as well as production of certain white blood cells. It produces lymphocytes and other cells to fight infection, stores healthy blood cells and filters out damaged or worn-out blood cells, platelets and cell waste.
  • Thymus. An organ located in the front of the chest at the base of the neck that is most active before birth. During fetal development and childhood, its main function is developing T lymphocytes (T cells), a type of white blood cell. The T cells mature in the thymus and then travel to the lymph nodes. The activity and size of the thymus diminish after birth. It continues to decline with age as it is gradually replaced by fat tissue. In an older patient, what appears to be a yellowish-colored thymus may reveal only small remnants of thymus tissue surrounded by fat.
  • Bone marrow. The soft, inner section of bone. It is composed of blood-forming cells, fat cells and tissues that support the growth of blood cells. There are two types of bone marrow, yellow and red. Found in the cavities of large bones, yellow marrow consists mainly of fat cells and a few primitive blood cells. Red marrow is tissue in which blood cells are produced. Blood cells produced in the bone marrow include:
    • White blood cells (to fight infections)
    • Red blood cells (carry oxygen to tissues in the body)
    • Platelets (help develop blood clots and control bleeding)
  • Adenoids and tonsils. These are masses of lymphoid tissue located at the back of the throat. Their role in the lymphatic system includes producing antibodies against antigens or other foreign materials that are breathed in or swallowed. Tonsils and adenoids often become swollen when they are fighting off an infection in the throat. Physicians may recommend that they  be surgically removed if they become chronically enlarged (e.g., after several attacks of tonsillitis).

Role in cancer response or spread

The lymphatic system is essential to the body’s response against cancer. It is also one of the body’s most common pathways for the spread of cancer cells to other areas of the body (metastasis).

Lymph nodes produce immune cells and filter foreign material including bacteria and cancer cells from lymph. When the lymph nodes recognize antigens or foreign materials in the lymph fluid, they respond by enlarging and producing additional including lymphocytes to help combat infection. In a person with cancer, immune cells patrol the body searching for cancer cells to destroy. Tumors develop when this immune response breaks down or is overwhelmed.

LymphomaAlso known as swollen glands, enlarged lymph nodes are usually not a serious concern. They are most often seen in people with infections such as sore throats and colds. However, an enlarged lymph node is the most common sign of lymphoma, or cancer of the lymphoid tissue. In this condition, tumors generally develop in the lymph nodes, but may occur in lymphatic tissue located in the stomach, intestines or other organs. Cancer may also develop in other parts of the lymphatic system, including the:

  • Bone marrow (multiple myeloma and lymphoblastic leukemia)
  • Adenoids
  • Tonsils
  • Thymus

Enlarged lymph nodes may be a sign that cancer has spread to the lymph nodes from another location. Cancer cells can easily break off from an initial tumor and enter the lymphatic system. Breast cancer, for example, can spread through the lymph vessels to the lymph nodes in the armpit (axillary nodes) and under the sternum (breast plate).

To determine whether a lymph node contains cancerous cells, a biopsy of the area may be ordered. The sentinel lymph nodes are the first lymph nodes to which cancer cells are likely to spread from a primary tumor. As a result, these lymph nodes are often removed and examined under a microscope to determine if the cancer has spread. In order to identify the sentinel lymph nodes, a process known as lymph node mapping may be performed. In this procedure, dyes and radioactive substances are used to identify lymph nodes that contain cancer cells. Once the sentinel lymph nodes have been identified, they may be surgically removed (excisional biopsy) or a sample may be removed for testing (incisional biopsy).

Researchers are studying how new blood vessels are formed promoting the spread of cancer cells to other areas of the body. Researchers are also working to develop ways to enhance the immune system’s response to cancer. One method under study is biological therapy or immunotherapy. This method uses substances naturally produced by the immune system to kill cancer cells, slow the growth of the cancer cells or activate the patient’s immune system to more successfully fight the disease.

Biological therapy agents currently being studied include monoclonal antibodies. These are antibodies produced in a lab to resemble those normally produced in the body. However, instead of attacking other antigens as normal antibodies do, monoclonal antibodies are designed to attack antigens on cancer cells. Some monoclonal antibodies have already been approved by the U.S. Food and Drug Administration (FDA) and are currently in use to treat certain types of cancer.

Lymphedema is a condition that can occur when the lymph system is obstructed. When lymph vessels are blocked, it may cause a buildup of lymph fluid in the tissues and result in swelling. It occurs most often in the arms or legs.

There are two types of lymphedema – primary and secondary. Primary lymphedema can occur when lymph nodes or lymph vessels are missing or are not working properly.

Secondary lymphedema is more common. It can develop as a result of cancer or cancer treatments, among other causes. During surgery for cancer, a surgeon may remove some of the lymph nodes located near the tumor for a biopsy. In some cases, lymph vessels may also require removal because they are wrapped around the lymph nodes.

Removing lymph nodes and lymph vessels makes it harder for lymph fluid to flow to other parts of the body. When the remaining lymph vessels fail to remove enough of the excess lymph in the area, the fluid can build up and cause swelling. Scar tissue from lymph node removal or radiation therapy can also cause blockage of the lymphatic system, therefore increasing the risk for lymphedema.

Lymphedema can occur after surgery or radiation therapy for any type of cancer, but is most common in patients with Breast cancer, prostate cancer, pelvic area cancers, lymphoma or melanoma.

Questions for your doctor

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their condition. Patients may wish to ask their doctor the following questions about the lymphatic system:

  1. How does the lymphatic system work?
  2. What is the function of the lymph nodes?
  3. What does it mean if I have swollen lymph nodes?
  4. What are the signs my lymphatic system is not working properly?
  5. Can I do anything to improve the functioning of my lymphatic system?
  6. Should my child have tonsils or adenoids removed if they are repeatedly swollen?
  7. What is metastasis and how does it relate to the lymphatic system?
  8. How do I know if my cancer is in my lymphatic system?
  9. How will this affect my prognosis?
  10. If I need a lymph node biopsy, what type will I receive?
  11. How is the sentinel node identified for biopsy?
  12. What will a lymph node biopsy tell me?
  13. If cancer is found in my lymph nodes, does it mean I have cancer elsewhere in my body?
  14. How can I prevent lymphedema if I undergo surgery?
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