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What is the lymphatic system?

The lymphatic system is fundamentally important to cardiovascular disease, infection and immunity, cancer, and probably obesity — the four major challenges in healthcare in the 21st century (Mortimer and Rockson)

What is the lymphatic system?

The lymphatic system has been described as the “sewer system” of the body.

Whilst the lymphatic system does move waste products that sit in the tissue space, through to lymph nodes for filtering, the lymphatic system is far more than the “sewer system” of the human body.

The lymphatic system is linked to major health problems:

  • cardiovascular disease and obesity through fat transportation and inflammatory processes – the lymphatic system playing a crucial role in the intestinal absorption of fats. Fats that are absorbed by the lymphatic system eventually end up in the blood. When the lymphatic system functions abnormally, abnormal fatty tissue deposition occurs. Cardiovascular disease involves a build up of fat in blood vessels and inflammatory processes which involve the lymphatic system in atherosclerosis can contribute to this process. (Atherosclerosis is a chronic inflammatory disease affecting large – to medium-sized arteries).
  • infection and cancer through the lymphatic systems role in immunity – lymph nodes monitor the lymph that flows into them and produce immune cells and antibodies that protect the body from infection and disease. The spleen and thymus are lymphatic organs that monitor the blood, detect pathogens and cancerous cells, and act accordingly.

When the lymphatic system is not functioning properly, it may contribute to obesity, Crohn’s disease, and other conditions involving chronic swelling (called oedema which is also spelled as edema). Body areas may swell if the lymphatic system is malformed or if it has been damaged by surgery, radiation, or tissue damage (most commonly the legs or arms). When this swelling persists for more than three months, whereby compromise to the lymphatic system is suspected, the condition is known as lymphoedema.

What are the functions of the lymphatic system?

The primary functions of the lymphatic system are:

  • Regulating the body’s fluid levels in response to pathogens, cancer cells, and cell products that would otherwise cause disease or disorders.
  • Managing fat in the absorption by absorbing a portion of dietary fats in the small intestine.
  • Circulating immune cells. Lymph nodes and other lymphatic structures, such as the spleen and thymus, contain specialised white blood cells known as lymphocytes. These cells can multiply rapidly and release antibodies in response to bacteria, viruses, and a variety of other stimuli from dead or dying cells and abnormally behaving cells such as cancer cells.

How does the lymphatic system control tissue swelling?

The lymphatic system eliminates fluids and their contents that leak into the tissues, as well as waste products formed in the tissues and bacteria that enter through the skin.

When the lymphatic system fails to properly drain fluids from the tissues, the tissues swell and become uncomfortable. If the swelling is temporary, it is referred to as oedema. If it persists for longer than three months, it is known as lymphoedema.

All chronic oedemas show that the lymphatic system is not functioning well enough in order to move fluids adequately out of the tissues.

What organs and vessels make up the lymphatic system?

The lymphatic system is a complex network of pipes throughout the body. It returns fluid (called lymph) that has leaked from the blood vessels into the tissues to the bloodstream via the lymph nodes.

The lymphatic system is part of the circulatory system.

Cardiovascular system + lymphatic system = circulatory system

What are the components of the lymphatic system?

Lymphatic capillaries

Lymphatic vessels are located throughout the body.


The smaller lymphatic vessels that absorb fluids are referred to as lymph capillaries. Larger lymphatic vessels have muscle in their walls, allowing them to pulse gently and slowly. These larger lymphatic vessels also contain valves that prevent lymph from flowing in the opposite direction.


Lymph vessels return lymph to the lymph nodes, which are located in the armpits, groin, as well as the mouth, throat, and intestines. There are approximately 700 lymph nodes in total.


The fluid entering the lymph nodes is examined and filtered.

About 30-50% of lymph re-enter the blood circulation at the level of regional lymph nodes. The remaining lymph drains deep into the thoracic duct which eventually empties into the bloodstream.



The spleen is situated on the left side of the abdomen, just below the diaphragm. It is the largest lymphatic organ in the human body.


The spleen filters and monitors our blood, among other functions. It contains a variety of cells, including macrophages, the garbage trucks of the body. It also produces and stores numerous cells, including a variety of white blood cells that are essential to our body’s immune system.


In addition to eliminating microbes, the spleen eliminates old or damaged red blood cells. It can also aid in rapidly increasing blood volume if a large amount of blood is lost.



The thymus is located just behind the breastbone, within the ribcage. It filters our blood and monitors its composition. It generates T-lymphocytes, which circulate throughout the body. These cells are essential for the cell-mediated immune response to a challenge, such as an infection.


Additional lymphoid tissue

Our digestive and respiratory tracts are largely lined with lymphatic tissue. It is necessary because these systems are exposed to the outside world. This lymphatic tissue plays a crucial role in our body’s defences.

Tonsils, Peyer’s patches, and the appendix are the most significant locations of this lymphoid tissue.


Lymph nodes

Lymph nodes function as filters. They are located throughout the body, including the neck, armpits, chest, abdomen, and groin. Typically, they form chains or groups. All are situated close to veins and arteries and are embedded in fatty tissue.


Lymph nodes serve a variety of purposes,  but are most commonly associated with body defence. Bacteria (or their by products) collected from the tissues by macrophage cells or those that enter the lymph are forced to percolate through the lymph nodes. There, white blood cells known as lymphocytes are able to attack and kill bacteria. Viruses and cancer cells are also captured and eliminated by lymph nodes.


When an infection exists, more lymphocytes are produced. When you have an infection, your lymph nodes tend to swell for this reason.


Frequent issues with the lymphatic system

Common lymphatic system issues can be separated into the following categories:

  • Infection
  • Disease, or
  • Harm to the lymphatic system or its lymph nodes
  • Poor functioning or formation of the lymphatic system

Examples of infection:

  • Symptoms of glandular fever include tender lymph nodes
  • Tonsillitis is the infection of the tonsils in the throat.
  • The disease Crohn’s is an inflammatory bowel disorder.

Example of disease:

Lymphatic system cancer is Hodgkin’s disease.

Example of harm to the system:

Secondary lymphoedema – When the lymphatic system is damaged by surgery or radiotherapy used to treat cancer, when soft tissues are damaged by trauma, or when the lymphatic system has some other structural or functional impairment.

Venous disease involves poor functioning of the venous valves. Swelling can overwhelm the veins and later on the lymphatics. This is called phlebolymphoedema – a type of secondary lymphoedema.

Examples of poor functioning or formation:

Primary lymphoedema is caused by an improperly formed lymphatic system. May present at birth as a limb or body part swelling, or may develop during puberty or later in life.

Lipoedema is abnormal fatty tissue accumulation

Where to get help

  • Your GP
  • You can see a qualified lymphoedema therapist


Mortimer PS, Rockson SG. New developments in clinical aspects of lymphatic disease. The Journal of clinical investigation. 2014 Mar 3;124(3):915-21. Access here

Milasan A, Ledoux J, Martel C. Lymphatic network in atherosclerosis: the underestimated path. Future science OA. 2015 Nov;1(4). Access here