The Lymphatic System

Written by Dr Sze Man WONG


The lymphatic system probably needs to be better known by the public as it looks complex.  Most people may not have a good understanding of this vital system of our body and how it works. 


The lymphatic system is an extensive drainage network that consists of vessels, nodes and organs that carry lymph throughout the body.  This system plays multiple key roles in our health; it helps our body maintain the fluid level, ensures our immunity against foreign invaders, and cleans our tissues from cellular waste.1 The lymphatic system is essential to the good functioning of our body, and any problem at any level of this system may seriously impact the person's life.


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What is the lymphatic system and how it works?
What is the lymphatic system and how it works?
The lymphatic system is a network of vessels that look like blood vessels. In the difference of the vascular system, the lymphatic system consists of lymph ducts, lymphatic vessels, lymph nodes and lymphoid organs that transport lymph throughout the body. The lymph, an extra colourless fluid collected from cells and tissues, contains different substances, including proteins, minerals, fat, and white cells, but also damaged cells, cancer cells and foreign particles. The nutrients are brought to any part of the body and provide nourishment to tissues. At the same time, the white cells help protect the body against infection.

The lymphatic system plays an essential role in the body's immune function; it forms the first line of defence against disease with the white cells.  When pathogens are detected, our body elicits an immune response and prevents the onset of illness. Lymphocytes, specialized white cells, fight against these microorganisms, such as bacteria and viruses but also against cancer cells. Once produced in the bone marrow, lymphocytes undergo their maturation process in different lymphoid organs.  They enter the circulation and are stored in lymph nodes and the spleen, where they scrutinize for hazardous microorganisms.2


Lymph nodes are small bean-shaped structures of lymphatic tissue.  Normal lymph nodes are usually less than 1 cm in diameter.3 They filter out waste and eliminate pathogens that they find in the lymph.  That explains why lymph nodes swell when exposed to an infection or cancer.  There are about 600 lymph nodes in the body, and some are clustered in the neck, armpits, abdomen, and groins.4 They might become apparent when they are under the skin and can be examined.


The other key function of the lymphatic system is to maintain the fluid level of the body. The system continuously collects excess fluid and proteins that leak out from the blood vessels and capillaries.  The drainage of this excess fluid is crucial as if this is impaired, fluid might accumulate in the body's tissues and swelling might happen. This phenomenon is called oedema when the effect is localized, or lymphoedema when this implies a larger area such as an arm or the whole leg.


Unlike our cardiovascular system, the lymphatic system does not have a heart pump to circulate its lymph. The flow of the lymphatic fluid is maintained by small valves in the lymphatic vessels and by the movement of our muscles. The less we move, the more stagnant the lymphatic system is. And if dehydration occurs, cellular waste and toxins consequently accumulate in tissues resulting in diverse metabolic and infectious complications.

Dysfunction of the lymphatic system
Dysfunction of the lymphatic system

The lymphatic system may not carry out its function due to various reasons such as obstruction of its vessels, direct damage to the system or a malformation before birth or during childhood.


Lymphatic obstruction may be caused by an infection with parasites such as filariasis, a tumor or surgery. These may cause lymphoedema, an accumulation of extra fluid that the patient might experience a heaviness of the limb, a restriction of his movement and a hardening of the skin. A common cause of lymphoedema is mastectomy which is the removal of the breast and underarm lymph nodes for breast cancer treatment.


Infection, inflammation, and cancer may cause a swelling of the lymph nodes (lymphadenopathy).  Any common infections may give rise to lymphadenopathy; that could be flu, streptococcal pharyngitis, mononucleosis, and infected skin wounds. When a patient has an upper respiratory infection, the lymph nodes of the neck enlarge as they react against the infection. They appear as small, soft, and tender lumps on the neck. But when the lymph nodes persist or enlarge without any pain, other causes of lymphadenopathy should be suspected. In this case, a healthcare provider should be consulted to rule out more serious condition. 


White blood cell cancer such as lymphoma starts in the lymph glands and then spread to other organs of the body. The patient might see some painless swollen lymph nodes anywhere on the body but also experience fever, drenching sweat, unintended weight loss and unexplained fatigue. The symptoms may be nonspecific and if they are persistent, a medical evaluation should be undertaken as soon as possible. There are 2 main types of lymphoma: Hodgkin lymphoma and non-Hodgkin lymphoma.  Risk factors for lymphoma are men aged in their 60s or older, a first degree relative known for lymphoma, exposure to benzene and certain insecticides and radiation. Treatment may differ depending on the type of lymphoma.6

When to see a doctor?
When to see a doctor?
Patient should seek medical attention when he notices a painless lump, a persistent swelling in the arm or leg or continuous feeling of fatigue or unexplained weight loss. A further medical evaluation shall be undertaken. Of course, if the patient is concerned for any other symptoms, even minor, he is welcome to seek medical advice and be reassured on their concerns. For many conditions, early detection can lead to better outcomes.
What do the doctors do to find the diagnosis?
What do the doctors do to find the diagnosis?

Once the patient notices a lymph node swelling, what will the doctors do in consultation?  This situation can be very stressful to the patient as he might considerably question about the origin of the lump.


To narrow the diagnostic possibilities, doctors usually start with a complete history by asking the patient a series of questions. Are there symptoms suggesting an infection? Were there any recent cat scratches, any ingestion of undercooked meat or any tick bite? Any constitutional symptoms such as fever, night sweat or weight loss? Any recent medications? Any family history of lymphoma? A careful history may differentiate between an infection and a cancer.


Doctors will then carry a careful physical examination and they usually start by examining the abnormal lymph node by evaluating its size, its location, its consistency, and its fixation to the surrounding tissues. Lymph nodes are also looked at other locations to exclude a generalized disease.  Then a more general physical examination is undertaken.


A viral infection is often obvious after a complete history and clinical examination.


Even if the probability is low, cancer is a diagnosis that doctors always keep in mind, especially when the patient presents some worrisome symptoms.  The risk for malignancy is 4% in patients older than 40 and 0.4% in those younger than 40.7 Malignant lymph nodes are usually firm and increase rapidly in size.  Patients might present general symptoms such as weight loss or fatigue. These patients should have more investigations, such as imaging and biopsy, for further evaluation.

The prevalence of lymphatic disease in Hong Kong
The prevalence of lymphatic disease in Hong Kong

Lymphoma is one of the top 10 cancers in Hong Kong. The subtype Hodgkin lymphoma has seen its incidence increase in recent years in Hong Kong, especially in the young male population. According to a study led by CUHK, 60% of new Hodgkin lymphoma cases were aged 44 years old or younger. In addition, morbidity and mortality from Hodgkin lymphoma are higher in populations with risk factors of smoking, obesity, and hypertension.8  


Lymphoedema is a well-known complication to treatment for breast cancer and gynaecological cancer. The treatment may seriously damage the lymphatic vessels and the lymph nodes, causing oedema. The prevalence of such complications ranges from 5% to 45%. In difference with blood vessels, the lymphatic system does not regenerate after being damaged, and lymphoedema often persists if no intervention occurs.9

How to keep our lymphatic system healthy?
How to keep our lymphatic system healthy?

There is no definitive cure for lymphedema once it sets up.  Physiotherapy and lymphedema massage are the mainstays of the treatment. Physiotherapists usually perform compression therapy that consists of manual lymphatic drainage and bandaging in the early stage of lymphoedema. Unfortunately, its efficacy is limited in severe lymphoedema.


In healthy people, maintaining an effective lymphatic system can be achieved with simple lifestyle routines. Keeping the lymphatic system healthy allows it to filter toxins and eliminate cancer cells, bacteria and viruses. Drinking plenty of water is one of the first healthy tips to boost the lymphatic system. Once you are dehydrated, less fluid will flow through the tissues, and more toxins and cellular waste will remain. The second tip is to exercise, so the lymph is squeezed through the lymphatic vessels during physical activity. As the lymphatic system has no heart pump, it relies on muscles to move the lymph through the body. Running, jumping, walking, stretching, and other daily exercises can improve your lymphatic system.  Massage and compression garments can also help in reducing swelling. The last tip is to have a healthy diet with plenty of green leafy vegetables and fruits.  Avoid processed foods, limit your consumption of caffeine and alcohol, and watch your body weight.10

The lymphatic system plays an important role in providing an immune response to harmful pathogens, maintaining fluid levels in the body and removing toxins and waste from tissues. This optimal condition is delicate, and even a simple infection might significantly affect the system. It is essential to look for medical attention when symptoms appear worrisome and intrusive. An enlarging painless lymph node or unexplained weight loss or fatigue should alert for further investigation. Keeping your lymphatic system healthy is one of the simplest ways to maintain your optimal health.
  1. Lymphatic system. Cleveland Clinic.
  2. Manda Null; Manuj Agarwal. Anatomy, Lymphatic system. National Library of Medicine. Last update: February 2022
  3. Evaluation of peripheral lymphadenopathy in adults. Up to date.
  4. University of Rochester, Medical Center.
  5. Lymphoedema. NHS.
  6. Cancer Research UK. CUHK
  7. Andrew M. Freeman, Patricia Matto. Adenopathy. National library of Medicine. Published February 2022.
  8. CUHK finds the largest rise in incidence of Hodgkin lymphoma in Asia Rising trend of male incidence means Hong Kong tops the world. Published June 2022.
  9. HKU Introduces the Latest Lymphedema Surgery to Hong Kong and Helps Patients Return to Normal Life. The University of Hong Kong. Published June 2016.,from%205%25%20to%2045%25.
  10. The lymphatic system and how to keep yours healthy. Published December 2019.

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