Topic Resources
The lymphatic system is a vital part of the immune system, along with the thymus, bone marrow, spleen, tonsils, appendix, and Peyer patches in the small intestine.
Like the venous system, the lymphatic system transports fluids throughout the body. The lymphatic system consists of
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Thin-walled lymphatic vessels
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Lymph nodes
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Two collecting ducts
Lymphatic vessels, located throughout the body, are larger
than capillaries (the smallest blood vessels, which connect arteries
and veins), and most are smaller than the smallest veins. Most of the
lymphatic vessels have valves like those in veins to keep the lymph,
which can clot, flowing in the one direction (toward the heart).
Lymphatic vessels drain fluid called lymph from tissues throughout the
body.
Lymph begins as fluid that has diffused through the very
thin walls of capillaries into the space between cells. Most of the
fluid is reabsorbed into the capillaries and the rest is drained into
the lymphatic vessels, which eventually return it to the veins. Lymph
also contains many other substances including
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Proteins, minerals, nutrients, and other substances, which provide nourishment to tissues
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Damaged cells, cancer cells, and foreign particles (such as bacteria and viruses) that may have entered the tissue fluids
Lymph nodes are collection centers for lymph. All lymph
passes through strategically placed lymph nodes, which filter damaged
cells, cancer cells, and foreign particles out of the lymph. Lymph nodes
also contain specialized white blood cells (for example, lymphocytes and macrophages)
designed to engulf and destroy damaged cells, cancer cells, infectious
organisms, and foreign particles. Thus, important functions of the
lymphatic system are to remove damaged cells from the body and to
provide protection against the spread of infection and cancer.
The Lymphatic System
The lymphatic vessels drain into collecting ducts, which
empty their contents into the two subclavian veins, located under the
collarbones. These veins join to form the superior vena cava, the large
vein that drains blood from the upper body into the heart.
Lymphatic System: Helping Defend Against Infection
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The lymphatic system is a vital part of the immune system, along
with the thymus, bone marrow, spleen, tonsils, appendix, and Peyer
patches in the small intestine.
The lymphatic system is a network of lymph nodes connected by
lymphatic vessels. This system transports lymph throughout the body.
Lymph is formed from fluid that seeps through the thin walls of
capillaries into the body's tissues. This fluid contains oxygen,
proteins, and other nutrients that nourish the tissues. Some of this
fluid reenters the capillaries and some of it enters the lymphatic
vessels (becoming lymph). Small lymphatic vessels connect to larger ones
and eventually form the thoracic duct. The thoracic duct is the largest
lymphatic vessel. It joins with the subclavian vein and thus returns
lymph to the bloodstream.
Lymph also transports foreign substances (such as bacteria),
cancer cells, and dead or damaged cells that may be present in tissues
into the lymphatic vessels and to lymph organs for disposal. Lymph
contains many white blood cells.
All substances transported by the lymph pass through at least one
lymph node, where foreign substances can be filtered out and destroyed
before fluid is returned to the bloodstream. In the lymph nodes, white
blood cells can collect, interact with each other and with antigens, and
generate immune responses to foreign substances. Lymph nodes contain a
mesh of tissue that is tightly packed with B cells, T cells, dendritic cells, and macrophages. Harmful microorganisms are filtered through the mesh, then identified and attacked by B cells and T cells.
Lymph nodes are often clustered in areas where the lymphatic vessels branch off, such as the neck, armpits, and groin.
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Lymphatic System
3D Model
Disorders of the lymphatic system
The lymphatic system may not carry out its function adequately due to
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Blockage (obstruction): Obstruction in the lymphatic system leads to an accumulation of fluid (lymphedema). Obstruction may result from scar tissue that develops when the lymph vessels or nodes are damaged or removed during surgery, by radiation therapy, by injury, or in tropical countries, by infection with a threadworm (filariasis) that blocks the lymphatic ducts.
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Infection: Infection may cause swollen lymph nodes because the lymph nodes are inflamed. Sometimes the lymph nodes themselves may become infected (lymphadenitis) by organisms that spread through the lymphatic system from the original site of infection.
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Cancer: Tumors may block the lymphatic ducts or may travel (metastasize) to lymph nodes near a tumor, interfering with flow of lymphatic fluid through the node. Rarely, a tumor (lymphangiosarcoma) may develop in the lymphatic system.
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