Lymphatic system
In addition to the blood system, our body has another transport system called the lymphatic system.
Clear fluid seeps out of blood capillaries into surrounding tissue cells. Called interstitial fluid, it helps deliver oxygen and nutrients to cells and carries away their waste. To deal with this seepage, the fluid drains into a system of tubes. The tubes increase in size from tiny lymph capillaries to lymph vessels. The vessels empty into lymphatic trunks and ducts, which finally link together into two large collecting ducts (the thoracic duct and the right lymphatic duct). The lymphatic fluid drains back into the blood system at the right and left subclavian veins just before the blood returns to the heart at the right atrium.
The human lymphatic system
The lymphatic system includes tubes of various sizes, lymph nodes and areas of lymphatic tissue such as the tonsils, spleen and bone marrow.
There is no pump in this drainage system – instead, muscles attached to your skeleton provide the force to move this fluid back to the blood system at the subclavian veins.
Lymph empties into the subclavian vein
Interstitial fluid drains from the tissues into the lymphatic system. When interstitial fluid enters the lymph vessels it becomes ‘lymph’ (lymphatic fluid). Lymph then drains back into the blood system through the left and right subclavian veins.
Adapted from the diagram 'Lymphatic Vessels, Trunks, and Ducts' by Julie Jenks, a derivative of the original work by Daniel Donnelly.
To help this one-way flow of fluid, there are semilunar valves in the veins that prevent lymph flowing backwards. When people are sitting in one place or their muscles are restricted from full movement, there can be a build-up of fluid in the tissue because the pumping action of the muscle is not able to aid the movement of fluid away from the tissue. When that happens, tissues may swell – this is called oedema.
Parallel circulation systems
Relationship between the blood circulation and lymphatic circulation systems.
One way of preventing oedema is to move your skeletal muscles so there is not a build-up of tissue fluid. This is why you are requested to carry out leg exercises when you are flying long distances on a plane. Also, when you are standing still for very long periods, you should gently back and forth.
Lymph nodes
At certain points on the larger lymphatic vessels, there are lymph nodes. Their function is to produce B cells (also called lymphocytes) that protect the body against infection.
Lymph nodes are distributed throughout the body, and you may have noticed that, when you are sick, your doctor may feel the lymph nodes in your neck or ask about the lymph nodes in your pelvic region. When the lymph nodes are swollen, it is a sign that the body is actively fighting an infection with the arsenal of cells and substances produced by this lymph node tissue.
The lymphatic system and melanoma
Professor Rod Dunbar describes the lymphatic system and explains its role in the spread of melanoma.
Select here to view video transcript, discussion questions and copyright information.
Metastasis
Scientists have discovered that cancer cells travel from the tumour through the lymphatic system, and this process is called metastasis. Scientists have developed a technique to map the closest lymph node to the tumour. Once this lymph node is identified, surgeons can remove this lymph node and carry out a biopsy (cross section and chemical test) to see if the cancer cells have travelled this far. This technique is called sentinel node biopsy.
Sentinel lymph nodes
Dr Elizabeth Baird and Professor Rod Dunbar discuss sentinel lymph nodes - the node or nodes where a cancer first spreads to, from the primary tumour.
Select here to view video transcript, discussion questions and copyright information.
Because of this new technique of detection, biopsy and treatment, there is a much greater chance that cancers will be detected before they spread, so there is more incentive for people to check on unusual growths on their bodies rather than ignoring them or denying that there might be a problem.
Related content
The lymphatic system is part of the immune system. Learn more in The body’s first line of defence and The Body’s second line of defence.
The boy in the bubble looks at the case of David Vetter, who was born with a rare inherited disease, which meant that his immune system didn’t work.
Fighting infection, the immune system – unit plan is designed to help teachers improve students’ ideas about the immune system and how it works to fight infection.
These two activities also look at our immune system: The wars within and the Fighting infection card game.
These articles explain skin cancer, melanoma, why New Zealand skin cancer rates are so high, some of the risk factors and how skin cancer is diagnosed and treated.
Read about the early research of biomedical engineer Dr Hayley Reynolds, to develop a Melanoma spread pattern model.
Activity ideas
Students can explore concepts around cancer in the activities Cancer definitions and Characteristics of normal and cancerous cells.
Useful links
A drawing made from a dissection of the lymph nodes and subclavian veins that is published in Gray’s Anatomy.
Check out this Encyclopaedia Britannica article for more information about the lymphatic system.
