This section provides a brief overview of the anatomy of the lymphatic system, along with a few diagrams to provide some understanding of this important system in our body. The copyrighted historical images utilized in this section are courtesy of the Dr. Vodder Schule, Austria.
The lymphatic system begins with delicate lymph vessels called angions, located in the top two layers of the skin. These vessels constitute 60% of the lymphatic system. Lymph angions are composed of a single layer of endothelial cells secured to connective tissue by collagen fibers to hold them in place. Angions are a ‘swinging flap valve’ that can move inward and outward with the flow of fluid. Once the fluid has entered the lymph angion the pressure of the fluid opens a lobed value allowing the lymph fluid to enter a pre-collector vessel. The pre-collectors then connect to larger collector vessels and move the fluid to regional lymph nodes.
Lymphatic pre-collectors and collectors are larger vessels than the angions with a similar wall structure to a vein, although the walls are thinner than that of a vein. Both the pre-collectors and collectors are wrapped with smooth muscle fibers which contract rhythmically at a rate of 5 – 10 beats per minute. This contraction moves lymph fluid along the vessels to the lymph nodes.
Lymphatic collectors move fluid through a series of lymph nodes on the way to the subclavian vein.
Several lymph collectors can enter a single node although only one or two collectors exit each node. The lymph collectors enter and exit the node in the same location as the artery and vein that feeds the lymph node.
The lymph node itself is made up of sinuses filled with immunological cells, such as lymphocytes and macrophages, that both identify and eliminate viruses, bacteria, cell debris, cancer cells, and other foreign substances that invade our body.
Each area of our body constitutes a different watershed. Each watershed drains to a particular region of lymph nodes. After the lymph fluid passes through these nodes it enters larger lymphatic trunks deep within the body. Ultimately, after travelling through the lymphatic trunks the lymph fluid empties into the subclavian vein at the base of the neck.
The lymphatic system is a separate and distinct system in the body structured for the purpose of transporting filtered fluid and suspended material back to the venous side of the vascular system. This is performed through a series of lymph vessels and nodes. Although the lymphatic system transports fluid to the circulatory system it is unlike the circulatory system in that it only moves fluid in one direction.
It is also important to note that the lymphatic system not only carry lymph fluid it also carries metabolic waste, inflammatory agents, dead cell particles, large proteins, and fat molecules away from the interstitial areas. In layman’s terms it is basically “the sewer system of the body”.
Lymph fluid is a clear, colorless fluid originating in the tissue spaces as interstitial fluid. It is made up of various proteins, living and non-living particles, large fatty acids (protein), and fluid. In fact the only difference between interstitial fluid and lymph fluid is where it is located. If it is in the interstitial space it is called interstitial fluid; if it is in the lymphatic system it is called lymph fluid.
The initial lymphatic vessels are called lymph angions and are located in the top two layers of the skin. Lymph angions collect lymph fluid from the interstitial space within our tissue. The lymph is transported from the initial lymph vessels by pre-collector and collector lymphatic vessels. These segments contain lymph valves to prevent the backflow of fluid, and are wrapped with smooth muscles to move the lymph forward through the lymphatic system.
As lymph fluid passes from one region of the body to the next it moves through regional lymph nodes where cells, microorganisms, and tissue debris are filtered out of the fluid. Antigens (foreign bodies) are also identified and destroyed by immune cells in the lymph nodes. The lymph fluid then collects in lymphatic trunks and enters the bloodstream in the subclavian vein, just before the venous arch above the heart.
The lymphatic system typically dumps one to two litres of lymph fluid into the subclavian vein every 24 hours. This amount can be increased to 10 times normal levels during an MLD session, prior to tapering back to the normal levels within a 24 – 36 hour period.
Once the lymph fluid enters the subclavian vein it mingles with the blood and passes through the kidney. In the kidney the large proteins are removed and the waste fluid and material is dumped into the bladder and subsequently urinated from the body.
A variety of mechanisms move the lymph fluid through the lymphatic vessels. While smooth muscle wraps the pre-collectors and collectors and can contract rhythmically to move the fluid along the vessels, a number of other factors also contribute. Changes in intra-thoracic pressure during diaphragmatic breathing creates what is known as a Venturi effect to draw lymph fluid through the vessels. In addition, as the lymph vessels are situated close to arterial blood vessels, arterial tension and contraction promotes lymph flow, as does muscular contraction from gentle exercise.
It is critical to our health for the lymphatic system to function properly as it is the transportation component of the immune system. If the lymphatic pathways become congested, damaged or blocked, or lymph nodes are removed or irradiated, lymphatic fluid, wastes and proteins build up in the tissue. As more and more large proteins reside in the tissue, without the lymphatic system to remove them, the colloid osmotic pressure in the tissue increases and more fluid filters from the vascular system into the interstitial area. Thus a protein rich edema called lymphedema forms.
The volume of the lymph fluid in the tissue depends on a number of factors acting on three elements described by the Starling Equilibrium. The three elements that impact this fluid equilibrium in the body include: the hydrostatic pressure within the vascular system, the colloid osmotic pressure relationship between the vascular system and the interstitial region, and the permeability of the blood capillaries.
These three elements can be affected by such factors as blood pressure, particularly venous pressure, the protein concentration level in either the blood or the interstitial area, which can change the osmotic relationship across the vascular membrane, and inflammation and edema which increases vascular permeability.
In order for the lymphatic load to be handled by the lymphatic system, the lymphatic system must be healthy and the elements described by the Starling Equilibrium must be in balance. Any disturbance to the lymphatic system or imbalance in the fluid equilibrium will result in the formation of edema in the region.