Did you know that your body has two circulation systems? One, of course, circulates blood. But the other – the lymphatic system – also reaches into all areas of your body to collect a clear fluid called lymph, filter it, and circulate it back into the bloodstream. As part of the immune system, the lymphatic system is crucial to helping your body fight disease and infection. Here’s how it works.

The journey begins
When blood is pumped out of the heart it enters the aorta, the body’s main artery. Smaller arteries branch off from the aorta and even smaller blood vessels branch off from these, until the outward journey ends at microscopically small capillaries. Fluid that contains oxygen, proteins, minerals, and other nutrients seeps through the thin walls of the capillaries into the body’s tissues to nourish them. Excess fluid (lymph), along with bacteria, viruses, cancer cells, and worn-out blood cells, is picked up by nearby lymphatic vessels for a return trip through the body. Blood, meanwhile, returns by way of the veins of the cardiovascular system.

Lymph makes stops along the way at lymph nodes, which are essentially filtering stations that remove bacteria, viruses, cancer cells, and other harmful substances from the fluid. Lymph nodes are round or kidney-shaped and can measure up to one inch in diameter. Most are clustered in areas where the lymphatic vessels branch off, such as the neck, armpits, and groin. However, you can also find lymph nodes along lymphatic vessels in the chest and abdomen and lymphoid tissue in other parts of the body. In fact, tonsils are actually lymphoid tissue that helps to filter out bacteria at the top of the throat.

A well-designed filter
Lymph nodes are well designed for their filtering task. Each contains a mesh of tissue in which infection-fighting white blood cells are packed. As lymph passes through the nodes, it is filtered through the mesh. Foreign substances are trapped, attacked by the white blood cells, and disposed of as waste. This activity can also trigger the rest of the immune system to respond.

Once through the lymph nodes, lymph travels to larger vessels that ultimately empty the filtered fluid into veins near the left and right sides of the neck. From there lymph re-enters the bloodstream and the process begins again.

What can go wrong?
Swollen or enlarged lymph nodes (“glands”) can mean a number of things, some relatively minor and some far more serious. For example, if you have a bacterial infection like strep throat, bacteria can accumulate in the nearby lymph nodes of the neck faster than the white blood cells and immune system can deal with them. This can cause inflammation and swelling. Lymphoid tissue itself can become infected and swollen, which is the case with tonsillitis. In both instances, appropriate antibiotics will almost always take care of the infection and return things to normal.

However, sometimes an enlarged lymph node can be of much greater concern. If cells in the lymphatic tissue itself begin to grow rapidly and erratically, they can form a mass of extra tissue – a tumor. Tumors can be either benign or malignant (cancerous). Cancer of the lymphatic system is called “lymphoma,” and there are several different types. Because lymphatic tissue is found throughout the body, lymphoma can start almost anywhere. As with other cancers, early detection is the key to a successful outcome.

A marvel of design
The lymphatic system is a network of vessels and filters that protects us against infection and disease, removes excess fluid from our tissues, and even alerts us to potentially serious health problems. As with every other system in the human body, it’s a marvel of design and detail, working in concert with other systems and organs as a defender of our good health.