The lymphatic system has two main functions. One is a secondary route for fluid back to the blood and heart. The other is a main function of the immune system.

I). Secondary route for fluid back to the blood and heart.
The heart pumps blood to the tissues of the body via the arteries, arterioles and arterial capillaries (largest to smallest vessels). The capillaries allow dissolved oxygen and nutrients from the blood to diffuse into the interstitial fluid (fluid between cells). Here the oxygen and nutrients enter cells. At the same time carbon dioxide and waste products leave the cells and returns to the blood and heart thru the venous system of vessels, smallest to largest (capillaries, venules, veins, inferior vena cava and superior vena cava. ) The venous system picks up about 80% of the fluid in the interstitial space.

The pressure from the pumping of the heart and gravity assist the delivery of oxygen and nutrients to the tissues, and there are no valves in the arterial system. The venous system (returning blood to the heart) goes against gravity and the pressure from the heart pumping is significantly reduced at this point. The venous system has valves to prevent backflow. If the veins have defective valves, they can become engorged and create varicosities.

Now, here is where the lymphatic system comes in. One of the nutrients in the interstitial space is proteins delivered by the arterial capillaries. They are too big to be picked up by the venous capillaries and so are picked up by the lymphatic capillaries. The lymphatic capillaries pick up approximately 20 % of the fluid that was delivered to the interstitial space. Fluid becomes lymph when it enters the lymph vessels. It is a high protein fluid.

The lymphatic system has small to large vessels ( lymph capillaries, precollectors, collectors and lymph trunks) like the arterial and venous system. There is a superficial system about a nails width under the skin. It is like a fine mesh that covers the whole body. It does not have valves or lymph nodes. There are links to a deeper system (gradually larger vessels) that have valves and lymph nodes that filter the fluid before it returns to the venous circulatory system. There is no central pump for the lymphatic system.

There are several ways lymph is encouraged to move, temperature, activity of muscle and joint pumps, diaphragmatic breathing, pulsation of adjacent arteries. The larger vessels have sections (sometimes referred to as a string of pearls and in some areas like the groin, it looks like a bunch of grapes) called angions with smooth muscle, so that when they fill up with lymph it causes a contraction.  This contraction squeezes the lymph out and filling the next angion and contracting, etc.  Manual Lymph Therapy also moves lymph in a very effective way.

This is the alternate route for returning fluid to the blood and heart.

II). The lymphatic system as a major function of the immune system.
As flulid enters the lymph vessels system it eventually is interrupted by lymph nodes. The lymph nodes have three main functions.

1. Protective (filtering dust, cancer cells, pathogens and dirt).
2. Immune function – responsible for producing lymphocytes (antibodies). Lymphocytes are white blood cells that circulate in the blood and lymphatic system. They harbor in the lymph nodes and spleen and are directly responsible (T-cells and macrophages), and indirectly (B-cells producing antibodies) for attacking invaders. Antibodies travel through the lymph vessels to where they are needed.
3. Thickening of lymph fluid – blood capillaries in the lymph nodes reabsorb water, thickening fluid.

There are 600 to 700 lymph nodes in the body. Their size varies, the number does not.  They are located all over the body along the deeper vessels.  There are also groups or strings of lymph nodes in strategic places like under the arms, neck, groin and abdomen.  These are referred to as regional nodes.  When moving lymph, we direct to these sites unless the area is compromised, then it is rerouted.

What is lymphedema?

When the lymphatics (lymph nodes or lymph vessels) have been compromised, they are not as effective at processing the lymph.  The lymph backs up causing swelling. Lymphedema.  The compromised lymphatics can be something you are born with, called congenital or primary lymphedema.  When lymph nodes are removed due to cancer or vessels are damaged by radiation, surgery the system is usually unable to process the lymph adequately, resulting in lymphedema.

Lymph can be rerouted through alternate vessels and routes, this is the work of Manual Lymph Therapy.