Understanding the Lymphatic System

INTRODUCTION

The treatment of lymphedema is based on the structures and functions of the lymphatic system. This article presents basic information about the lymphatic system as it relates to the lymphedema care provided by patients as self-care and by caregivers who are aiding lymphedema patients. A qualified lymphedema therapist must have a more extensive understanding of this body system that is presented here.

FUNCTIONS OF THE LYMPHATIC SYSTEM

The lymphatic system works in close cooperation with other body systems to perform these important functions:

• The lymphatic system aids the immune system in destroying pathogens and filtering waste so that the lymph can be safely returned to the circulatory system.
• To remove excess fluid, waste, debris, dead blood cells, pathogens, cancer cells, and toxins from these cells and the tissue spaces between them. 
• The lymphatic system also works with the circulatory system to deliver nutrients, oxygen, and hormones from the blood to the cells that make up the tissues of the body.

In lymphedema affected tissues, the lymph is unable to drain properly. Instead within these swollen tissues the protein-rich lymph becomes stagnant. When bacteria enter this fluid through a break in the skin, they thrive on this protein-rich fluid. It is for this reason that lymphedema affected tissues are prone to infections. 

Blood capillaries allow fluid to leave, and enter, the circulatory system.

THE ORIGIN OF LYMPH

Lymph originates as plasma, which is the fluid portion of blood. The arterial blood that flows out of the heart slows as it moves through a capillary bed (see figure above). This slowing allows some plasma to leave the arterioles and flow into the tissues where it becomes tissue fluid.

• Also known as extracellular fluid, this is fluid that flows between the cells but is not found within the cells. This  fluid delivers nutrients, oxygen, and hormones to the cells.
• As this fluid leaves the cells, it takes with it cellular waste products and protein cells.
• Approximately 90 percent of this tissue fluid flows into the venules. Here it enters the venous circulation as plasma and continues in the circulatory system.
• The remaining 10 percent of the fluid that is left behind is now known as lymph.

BLOOD FLOW COMPARED WITH LYMPHATIC FLOW 

Lymph returning to the subclavian veins. © Lymph Notes

The bloodstream is pumped by the heart. It circulates throughout the body and is cleansed by being filtered by the kidneys. The lymphatic system does not have a pump to aid in its flow, instead this system is designed so that lymph only flows upward through the body traveling from the extremities (feet and hands) and upward through the body toward the neck.

As it travels through the body, lymph passes through lymph nodes where it is filtered. At the base of the neck, the lymph enters the subclavian veins and once again becomes plasma in the bloodstream.

LYMPHATIC CAPILLARIES

In order to leave the tissues, the lymph must enter the lymphatic system through specialized lymphatic capillaries. Approximately 70 percent of these are superficial capillaries that are located near, or just under, the skin. The remaining 30 percent, which are known as deep lymphatic capillaries, surround most of the body’s organs.

Lymphatic capillaries begin as blind-ended tubes that are only a single cell in thickness. These cells are arranged in a slightly overlapping pattern, much like the shingles on a roof. Each of these individual cells is fastened to nearby tissues by an anchoring filament.

As shown in the animation below, pressure from the fluid surrounding the capillary forces these cells to separate for a moment to allow lymph to enter the capillary. Then the cells of the wall close together. This does not allow the lymph to leave the capillary. Instead it is forced to move forward.

Lymph entering a lymph capillary. (Courtesy of John Ross).

LYMPHATIC VESSELS

A functioning lymphangion (Courtesy of Laura Niklason)

The lymphatic capillaries gradually join together to form a mesh-like network of tubes that are located deeper in the body. As they become larger, these structures are known as lymphatic vessels.

• Deeper within the body the lymphatic vessels become progressively larger and are located near major veins.
• Like veins, lymphatic vessels, which are known as lymphangions have one-way valves to prevent any backward flow.
• Each angions is a segment created by the space between two sets of valves.
• Smooth muscles in the walls of the lymphatic vessels cause the angions to contract sequentially to aid the flow of lymph toward the thoracic region. Because of their shape, these vessels are previously referred to as a string of pearls.

LYMPH NODES

There are between 600-700 lymph nodes present in the average human body. It is the role of these nodes to filter the lymph before it can be returned to the circulatory system. Although these nodes can increase or decrease in size throughout life, any nodes that has been damaged or destroyed, does not regenerate.

Lymph nodes kill pathogens and cancer cells. They also remove debris and excess fluid..© Lymph Notes

• Afferent lymphatic vessels carry unfiltered lymph into the node. Here waste products, and some of the fluid, are filtered out.
• In another section of the node, lymphocytes, which are specialized white blood cells, kill pathogens that may be present. This causes the swelling commonly swelling known as swollen glands.
• Lymph nodes also trap cancer cells and slow the spread of the cancer until they are overwhelmed by it.
• Efferent lymphatic vessels carry the filtered lymph out of the node to continue its return to the circulatory system.

Lymphatic Drainage Areas © Lymph Notes

DRAINAGE AREAS

Lymphatic drainage is organization into two separate and very unequal drainage areas. These are the right and left drainage areas and normally lymph does not drain across the invisible lines that separate these areas. Structures within each area carry lymph to its destination, which is to return to the circulatory system. 

Right Drainage Area	Left Drainage Area
Right drainage area landmarks © Lymph Notes	Left lymphatic drainage landmarks © Lymph Notes
Drains lymph from the right side of the head and neck The right arm Upper right quadrant of the body. Lymph from this area flows into the right lymphatic duct. This duct empties the lymph into the right subclavian vein.	Drains lymph from the left side of the head and neck The Left arm and the left upper quadrant The lower trunk and both legs The cisterna chyli temporarily stores lymph as it moves upward from the lower areas of the body. The thoracic duct transports lymph upward to the left lymphatic duct. The left lymphatic duct empties the lymph into the left subclavian vein.

WHY THIS INFORMATION IS SO IMPORTANT

• Damage disturbs the flow. When lymphatic tissues or lymph nodes have been damaged, destroyed or removed, lymph cannot drain normally from the affected area. When this happens excess lymph accumulates and results in the swelling that is characteristic of lymphedema.
• Drainage areas. The treatment of lymphedema is based on the natural structures and the flow of lymph. The affected drainage area determines the pattern of the manual lymph drainage (MLD) and for self-massage. Although lymph does not normally cross from one area to another, MLD stimulates the flow from one area to another. It also encourages the formation of new lymph drainage pathways.
• MLD treatment and self-massage begin by stimulating the area near the terminus and the larger lymphatic vessels. This stimulates the flow of lymph that is already in the system and frees space for the flow of the lymph that is going to enter the capillaries during the treatment.
• MLD treatment continues as a gentle massage technique to stimulate the movement of the excess lymph in affected tissues. The rhythmic, light strokes of MLD provide just the right pressure to encourage this excess lymph to flow into the lymph capillaries.
• The compression garments, aids, and/or bandages that are worn between treatments help control swelling by providing pressure that is needed to encourage the flow of lymph into the capillaries.
• Exercise is important in the treatment of lymphedema because the movements of the muscles stimulate the flow of the lymph into the capillaries. Wearing a compression garment during exercise also provides resistance to further stimulate this flow.
• Self-massage or simplified lympatic drainage, as prescribed by your therapist, is another way in which lymph is encouraged to flow into the capillaries. Each self-massage session begins at the terminus with strokes to stimulate the flow of lymph that is already in the system. This is followed by specialized strokes that encourage the flow of lymph into the capillaries and then upward to the terminus. 

REFERENCES

[1] About the Lymphatic System in The Lymphoedema Handbook by Professor N. Piller and M.O. O’Conner, P.T. Hill. Content 2002.

[2] Anatomy Fundamentals by W. Weissleder, and C. Schuchhardt in Lymphedema Diagnosis and Therapy 2nd ed. Kagerer Kommunikation, Bonn 1997

[3]  Foundation of Manual Lymph Drainage 3rd ed by M. Földi and R. StröBenreuther. Elsevier, 2003.

[4]  The Human Body Explained by P. Whitfield. Henry Holt and Company.

[5] Living Well with Lymphedema by A. Ehrlich, MA, A. Vinjé-Harrewijn PT, CLT-LANA, and E. McMahon. PhD. Lymph Notes, 2005.

[6] Lymphatic Vessels by A. Gashev in The Lymphatic Continuum Revisited ed by S.G. Rockson, 2008.

[7 Lymphedema Caregiver’s Guide by M. K. Kearse, PT, CLT-LANA, E. McMahon, PhD, and A.Ehrlich, MA. Lymph Notes 2009.

[8] Lymphedema Management: The comprehensive Guide for Practitioners, 2nd ed. by J.E. Zuther. Thieme, 2009.

[9] Lymphedema Therapy in a Vascular Anomaly Patient: Therapeutics for the Forgotten Circulation by S. G. Rockson in Lymphatic Research and Biology, Vol 3, No 4," 2005.

[10] The Lymphatic System Pathology by B. Lasinski in Implications for the Physical Therapists 2-Ed by C.C. Goodman, W.G. Boissonnault, and K.S.Fuller. Saunders, 2003, pages 477-508.

[11] The Way We Work by D. Macaulay and R. Walker. Houghton Mifflin Company, 2008.

[12] Unlocking the Drains by P. Brown. Nature Publishing Group, 2005, pages 459-458.

© LymphNotes.com 2010. This information does not replace the advice of a qualified health care professional.

Got a question or comment? Post in the 'The Lymphatic System' forum.
Category: The Lymphatic System Updated: 2011-11-30