About the Lymphatic System

The amount of water in the human body averages about 60% of total body weight. The average adult weighing 154 lbs. has about 10 and 1/2 gallons of water in their body.
That water is divided into 2 categories:
  1) the intracellular compartment: about 66% of that water is inside the cells.
  2) the extracellular compartment: about 33% of that water is outside the cells in blood, lymph and interstitial fluid.

The lymphatic system belongs to the circulatory apparatus, which provides one way for the blood to leave the heart - the arterial system, and two ways for it to return - the venous and lymphatic pathways. It parallels the venous system. Contrary to the blood circulation, the lymphatic circulation is one way, has a low velocity, low pressure, and a slow rhythm.

Fluid from blood vessel capillaries diffuses into the interstitial fluid. The interstitial fluid is very important because it is the fluid in which the cells are immersed, receive nutrition and release damaging by-products into. The lymphatic system drains this interstitial fluid of harmful waste products, first entering the lymphatic capillaries (walls of which are one cell thick) where it is then called lymph. This lymph is then transported to increasingly larger vessels, moving from pre-collectors to collectors, to ducts then to trunks, eventually dumping back into the venous circulation just under the collarbone. It is the lymph collectors that are the main transporting vessels of the lymphatic system. These collectors have valves and muscular units, lymphangions, which carry the lymph to the lymph nodes. The lymph nodes are filtration and purification stations, and destroy or disable microbes and produce lymphocytes. When the flow of lymph through the nodes increases - as through LDT - lymphocyte production increases.

The lymphatic system consists of 3 main elements:
  1) The lymph vessels: lymph capillaries, pre-collectors, collectors, trunks and ducts
  2) The lymph nodes (which also form part of the secondary lymphoid organ system)
  3) lymph fluid

The lymphoid organs consist of the various tissues and organs linked to the immune system which produce and/or store large numbers of lymphocytes and related cells. There are primary and secondary lymphoid organs. The primary lymphoid organs, the bone marrow and the thymus, are the sites for lymphocyte production and maturation. The secondary lymphoid organs store lymphocytes and destroy or disable antigens. They are lymph nodes, spleen, and M.A.L.T. (Mucosa-Associated Lymphoid Tissue): Peyer's patches (in the submucosa of the distal ileum), tonsils, appendix, and other locations throughout the body.

The lymphatic circulation is separated into two categories:
  1) The superficial: just under the dermo-epidermic junction and is not directly stimulated by exercise.
  2) The deep: in the muscles and the organs, which is stimulated by muscle contraction.

The lymphangions, on the collectors, contract at 5-8 per minute, which may be higher during exercise. These rhythmic peristaltic waves of contractions are central to the lymph circulation. When stimulated these lymphangions can increase the flow through the lymphatic system by 20-30 times.

Factors that increase lymphatic flow: Deep breathing increases flow into the thoracic duct; skeletal muscles contractions; peristalsis of visceral smooth muscles; contractions of adjacent arteries; active or passive motion of the limbs; external compression as in LDT, pressure of water during swimming, or the external counter-pressure exerted by bandages. During exercise drainage of the deep lymphatic circulation increases by 5-15 times.