Many people think that the lymphatic system serves as a ‘secondary’ or ‘back up’ to the blood. Yet when we delve deeper into the physiology of this remarkable system, its importance to protecting our bodies suddenly seems indispensable. The lymphatic system in vertebrates is an organ system, forming part of both the immune and circulatory systems. When tissue fluid (see left) is forced out of the blood capillaries, around 90% of it seeps back into the blood stream. The remaining 10% of tissue fluid, now called interstitial fluid, drains into lymph capillaries. This is know as lymph fluid (see left), and it has a similar composition to that of blood plasma. Lymph fluid is transported around the body in an akin manner to blood, in the sense that its movement through larger lymph vessels (lymph ducts) and lymph nodes (see below) is aided by valves and muscle contractions. These ducts are divided into a right and the much larger left side (the thoracic duct, which drains around 75% of lymph), and each duct is responsible for their own ‘sides’ of the body. The right and left ducts empty the lymph fluid into the right and left subclavian veins (under the collar bone) respectively, and hence the lymph fluid is returned to the bloodstream.
The main function of the lymphatic system is to transport lymph around the body, and ultimately returning it to the blood. However, it also plays a vital role in the removal of waste material and toxins. Lymph fluid is rich in leukocytes (white blood cells), which are responsible for protecting against and destroying pathogens that enter the body. As briefly mentioned before, there are essential bean-shaped structures throughout the lymphatic system, called lymph nodes, in which the majority of leukocytes are contained in. Lymph fluid is circulated within these lymph nodes (which are mostly located in the head, neck, armpits and groin), thus destroying toxins and pathogens that cause the body harm. Additionally, the system flushes out excess fluid from body tissues, which would otherwise cause bloating/oedema (see below), as well as the absorption and subsequent transport of fats to the circulatory system.
Whilst the lymphatic system plays a role in transporting vital substances around the body, this inadvertently means surviving pathogens or abnormal cells have another mechanism, apart from the blood, for circulating the body. As mentioned previously, the lymph nodes are the primary site where white blood cells destroy harmful pathogens. Hence, during an infection, the production of these white blood cells rapidly increases to counteract the disease, causing the lymph nodes to swell (inflammation). This response is deemed as lymphadenopathy, more specifically noted as local lymphadenopathy if a small number of lymph nodes are enlarged. General lymphadenopathy, when lymph nodes all around the body are enlarged, is caused by more serious bodily infections, such as HIV, cancer and arthritis.
Oedema is a swelling caused by a build up of fluid in tissue/cavities of the body. If this fluid consists of primarily lymph, the condition is coined lymphedema, arising from damage or a ‘malfunction; of the lymphatic system. Although the causes of lymphedema are largely unknown, a parasitic infection of lymphangiomatosis (lesions/cysts of the lymphatic vessels) are considered to be the most likely causes, as well as from the result of removal of the lymph nodes via surgery. As with other cases of oedema, this condition can be treated using manual drainage or compressive garments.
Cancer of lymphatic tissue is known as a lymphoma. A lymphoma is classified as ‘Hodgkin’ or ‘non-Hodgkin’, with a Hodgkin lymphoma causing a largely painless and “rubbery” lymphadenopathy. Conversely, a non-Hodgkin lymphoma, characterised by a large increase in the number of B- and T-cells, yields an extensively poorer outcome/prognosis for the patient (depending on whether it is high-grade or low-grade). However, this is attributed to by the fact that non-Hodgkin lymphomas occurs in older people.
Unfortunately, the role of the lymphatic system in transport means cancers from certain parts of the body can also be transported to other parts; when a group of cancer cells, which have “broken away” from the primary tumour, settle in the lymph nodes, the new tumour is known as a ‘secondary LN metastasis’. Nevertheless, with adequate medical care, over 85% of lymphoma patients survive for over 5 years after diagnosis, and can still be treated successfully with an S4 lymphoma.
Colbert, T. (2016) Stage 4 Lymphoma: Facts, Types, Symptoms, and Treatment. Available from: https://www.healthline.com/health/lymphoma/stage-iv.
Lymphoma Action (n.d.) The Lymphatic System. Available from: https://lymphoma-action.org.uk/about-lymphoma-what-lymphoma/lymphatic-system.
Lymph Node Diagram (2016) Wikimedia Commons. Available from: https://commons.wikimedia.org/wiki/File:Lymph_Node_Diagram_Unlabeled.jpg.
Lymphoma Research Foundation (n.d.) About Lymphoma. Available from: https://lymphoma.org/aboutlymphoma/.
‘Lymphatic System’ (2020) Wikipedia. Available from: https://en.wikipedia.org/wiki/Lymphatic_system#Clinical_significance.
Raeburn, P. (2018) How Is Non-Hodgkin Lymphoma Treated? Available from: https://www.everydayhealth.com/lymphoma/guide/nhl-treatment/.