The lymphatic system is an extensive drainage network that helps keep bodily fluid levels in balance and defends the body against infections.

The lymphatic system is made up of a network of lymphatic vessels. These vessels carry lymph — a clear, watery fluid containing protein molecules, salts, glucose, urea, and other substances — throughout the body.

The spleen is located in the upper left part of the abdomen under the ribcage. It works as part of the lymphatic system to protect the body, clearing worn-out red blood cells and other foreign bodies from the bloodstream to help fight off infection.

Why They're Important

One of the lymphatic system's major jobs is to collect extra lymph fluid from body tissues and return it to the blood. This process is important because water, proteins, and other substances are continuously leaking out of tiny blood capillaries into the surrounding body tissues. If the lymphatic system didn't drain the excess fluid from the tissues, the lymph fluid would build up in the body's tissues and they would swell.

The lymphatic system also helps defend the body against germs like viruses, bacteria, and fungi that can cause illnesses. Those germs are filtered out in the lymph nodes, which are small masses of tissue located along the network of lymph vessels. The nodes house lymphocytes, a type of white blood cell. Some of those lymphocytes make antibodies, special proteins that fight off germs and stop infections from spreading by trapping disease-causing germs and destroying them.

The spleen also helps the body fight infection. The spleen contains lymphocytes and another kind of white blood cell called macrophages, which engulf and destroy bacteria, dead tissue, and foreign matter and remove them from the blood passing through the spleen.

Basic Anatomy

The lymphatic system is a network of very small tubes (vessels) that drain lymph fluid from all over the body. The major parts of the lymph tissue are located in the bone marrow, spleen, thymus gland, lymph nodes, and the tonsils. The heart, lungs, intestines, liver, and skin also contain lymphatic tissue.

One of the major lymphatic vessels is the thoracic duct, which begins near the lower part of the spine and collects lymph from the pelvis, abdomen, and lower chest. The thoracic duct runs up through the chest and empties into the blood through a large vein near the left side of the neck. The right lymphatic duct is the other major lymphatic vessel. It collects lymph from the right side of the neck, chest, and arm, and empties into a large vein near the right side of the neck.

Lymph nodes are round or kidney shaped. They can be up to 1 inch in diameter. Most of the lymph nodes are found in clusters in the neck, armpit, and groin area. Nodes are also located along the lymphatic pathways in the chest, abdomen, and pelvis, where they filter the blood. Inside the lymph nodes, lymphocytes called T-cells and B-cells help the body fight infection. Lymphatic tissue is also scattered throughout the body in different major organs and in and around the gastrointestinal tract.

The spleen helps control the amount of blood and blood cells that circulate through the body and helps destroy damaged cells.

How It Works

Carrying Away Waste

Lymph fluid drains into lymph capillaries, which are tiny vessels. The fluid is then pushed along through the capillaries when a person breathes or the muscles contract. The lymph capillaries are very thin, and they have many tiny openings that allow gases, water, and nutrients to pass through to the surrounding cells, nourishing them and taking away waste products. When lymph fluid leaks through in this way it is called interstitial fluid.

Lymph vessels collect the interstitial fluid and then return it to the bloodstream by emptying it into large veins in the upper chest, near the neck.

Fighting Infection

Lymph fluid enters the lymph nodes, where macrophages fight off foreign bodies like bacteria, removing them from the bloodstream. After these substances have been filtered out, the lymph fluid leaves the lymph nodes and returns to the veins, where it re-enters the bloodstream.

When a person has an infection, germs collect in the lymph nodes. If the throat is infected, for example, the lymph nodes of the neck may swell. That's why doctors check for swollen lymph nodes (sometime called swollen "glands" — but they're actually lymph nodes) in the neck when your throat is infected.

Things That Can Go Wrong

Certain diseases can affect the lymph nodes, the spleen, or the collections of lymphoid tissue in certain areas of the body.

• Lymphadenopathy. This is a condition where the lymph nodes become swollen or enlarged, usually because of a nearby infection. Swollen lymph nodes in the neck, for example, can be caused by a throat infection. Once the infection is treated, the swelling usually goes away. If several lymph node groups throughout the body are swollen, that can indicate a more serious disease that needs further investigation by a doctor.
• Lymphadenitis. Also called adenitis, this inflammation of the lymph node is caused by an infection of the tissue in the node. The infection can cause the skin overlying the lymph node to swell, redden, and feel warm and tender to the touch. It usually affects the lymph nodes in the neck and is often caused by a bacterial infection that can be easily treated with an antibiotic.
• Lymphomas. These cancers start in the lymph nodes when lymphocytes undergo changes and start to multiply out of control. The lymph nodes swell, and the cancer cells crowd out healthy cells and may cause tumors (solid growths) in other parts of the body.
• Splenomegaly (enlarged spleen). In someone who is healthy, the spleen is usually small enough that it can't be felt when you press on the abdomen. But certain diseases can cause the spleen to swell to several times its normal size. Most commonly, this is due to a viral infection, such as mononucleosis. But in some cases, more serious diseases such as cancer can cause the spleen to expand.

If you have an enlarged spleen, your doctor will probably tell you to avoid contact sports like football for a while. If you're hit, the swollen spleen is vulnerable to rupturing (bursting). And if it ruptures, it can cause a huge amount of blood to be lost.

• Tonsillitis. Tonsillitis is caused by an infection of the tonsils, the lymphoid tissues in the back of the mouth at the top of the throat that normally help to filter out bacteria. When the tonsils are infected, they become swollen and inflamed, and can cause a sore throat, fever, and difficulty swallowing. The infection can also spread to the throat and surrounding areas, causing pain and inflammation. Someone with repeated tonsil infections may need to have them removed in a procedure called a tonsillectomy.

Reviewed by: Yamini Durani, MD
Date reviewed: October 2012