The Lymphatic System essentially, provides a way for fluid and particulate matter to move from interstitial spaces (AKA tissue space - this is the space outside of and between our cells) into the blood.  Return of fluid and matter, particularly larger proteins, from the tissue space to the blood is an essential function. 
Lymphatic System Components include lymph capillaries, lymph vessels, lymph ducts, and lymph itself which is a fluid.  Some include lymph nodes as part of the lymphatic system, while others consider nodes to be more a part of the immune system. 
     In our blood circulatory system, way at the end of the line in the tiniest capillaries, fluid filters out of the capillaries and into tissue spaces where it can reach individual cells in need of nourishment and waste removal.  Most of that fluid is reabsorbed into the venous side of those tiniest capillaries and continues on in the blood circulatory system.  But a small percentage of the fluid enters the lymphatic system instead.  This fluid is known as Lymph.  In normal conditions, 2-3 liters of this (usually) clear, colorless fluid enters the system each day.  Almost all tissues in the body have lymph channels that drain excess fluid directly from these interstitial spaces.
     Lymph capillaries are the first, smallest vessels to receive lymph.  These capillaries are microscopic, anchored to surrounding connective tissue and uniquely arranged to have minute valves that allow lymph to push into the capillary, but do not allow backflow.  As capillaries merge into bigger lymph vessels, valves continue to control the movement of lymph continually in one direction -- from superficial to deep and ultimately toward the heart.  Most of the body's lymph is headed for the thoracic duct.  This duct gathers lymph from all of the lower body and abdomen, the left side of the head, the left arm and parts of the chest.  In an adult it is 15-18 inches long, running from the lower spine alongside the aorta up to the cervical spine and emptying into the bloodstream at the juncture of the left subclavian and internal jugular vein.  The lymph from the right side of the head and neck, right arm and parts of the right side of the chest empty into the venous blood via the right lymph duct at the juncture of the right subclavian vein and internal jugular vein.  This duct is a much shorter trunk - only about one-half inch.
     One component that is missing from the lymphatic circulatory system is a pump - it does not have a "heart" to move the lymph through.  The vessels themselves do a small amount of contraction to move lymph. but external forces are a bigger factor in lymph movement.  The 2 most important external forces are nearby muscle contraction and body movement in general.  
Lymph System Functions.  When things are working well, lymphatic circulation is a carefully balanced flow, keeping the rate of return of fluid and proteins to the blood even with their leakage from the blood capillaries.  This balance is influenced by capillary pressure and permeability and the osmotic pressures of both plasma and interstitial fluid.  If any of these factors fall out of balance, or if there is a blockage in a lymph vessel at any point there will be a build up of fluid which is known as lymphedema.  This can be just a temporary nuisance, but chronic lymphedema can result in more serious medical problems. 
     A specialized lymphatic vessel known as a lacteal is critical to the absorption of fat from our diets.  Lymph fluid in the lacteals is known as chyle and looks milky due to the absorbed fat particles.
     Finally, lymph flows through lymph nodes on its way back to the bloodstream.  Lymph nodes are the filtration part of our immune system.  They keep particulate matter found in the lymph fluid out of the bloodstream.  Lymph nodes are full of specialized cells that destroy bacteria and other foreign materials.  When you have an infection and notice that you have swollen nodes, often in your neck, this is because the nodes are doing their job - working extra hard to eliminate the infection that has passed into them.  This is also what makes lymph nodes important in matters of cancer.  Cancer cells may be cleared from the surrounding tissue spaces and end up captured in lymph nodes.  If nodes are overwhelmed with any particular kind of foreign cells - whether it be cancer or an infectious bacteria - their ability to contain them may be compromised and a more serious infection or metastatis may be the result. 
Keeping the Lymphatic System Happy!  Moving lymph is happy lymph.  Perhaps you have had the experience of being on your feet in a relatively stationary position for the larger part of a day and finding your feet and ankles swollen by the end of the day.  Your lymphatics have been struggling against gravity all day with little assistance from muscular activity to move it up toward the heart.  So the vessels are full, but fluid continues to gather in the tissue space.  When it cannot get into the lymph capillaries, it has nowhere else to go, so just pools there in the tissue spaces of the feet and ankles.  If you go home and put your feet up, gravity is no longer working against the lymph.  If you go for a walk, the muscle activity will propel the lymph along.  In both cases, the edema will resolve.  But the walking will resolve it more quickly.  Lymph movement at rest is fairly slow.  Movement of the body and contraction of muscles around the lymph vessels increase the flow of lymph 10-30 times!  Another form of movement particularly good for lymph flow is rebounding - bouncing on a mini-trampoline.  5-10 minutes a day will help keep lymph moving.
    Massage helps move lymph.  For those with a chronic and/or severe edema problem, or post-surgical patients, a specific type of lymphatic drainage massage might be best.  For those in generally good health, all massage helps with this.  Self-massage works too!  If you find a swollen lymph node, work around it, not directly on it.
   Dry brushing is another wonderful habit for lymphatic and skin health.  Using a dry, natural-bristle brush, begin at the soles of your feet and brush either in long strokes or circles, moving up the legs and torso toward the heart.  With arms raised, brush them down toward the heart.  Do this before your shower to invigorate your skin, slough dead skin cells and, of course, move lymph!
   And always be sure you are drinking enough good, clean water!  Lymphedema is not caused by drinking too much water!  Your body needs plenty of water to keep everything moving, lubricated, and working at its peak. 
     Get medical attention for any chronic, unresolving edema, sudden onset edema or edema with red streaks.  Edema caused by obstructions or complications involving infection require other interventions.