Understanding the lymphatic system

A significant number of people are simply not aware that besides the blood circulation system, the body has another circulation system – the lymphatics.

What does the lymphatic system do?

The lymphatic system has three main functions.

Fighting infection
The lymphatic system transports a watery clear fluid full of proteins and lymphocytes. Lymphocytes are defence cells (infection-fighting cells). The fluid maybe yellow to milky white in colour, depending on where it is within the lymphatic system, and is known as lymph.

Draining excess fluid
As the blood circulates through the body’s tissues, it leaves behind waste products such as proteins and fluids. The excess fluid is drained through capillaries and into the lymphatic system where it is filtered and the clean fluid is returned to the blood.

Lipid (fat) absorption:
The lymphatic system also absorbs lipids from the intestine and transports them to the blood.

Your lymphatic system runs throughout your entire body and is parallel to the venous and arterial system (commonly known as the bloodstream). However, unlike your veins, the lymphatic system is not a closed system and has no central pump (i.e. your heart). It consists of hundreds of lymph nodes, lymph vessels, and lymph capillaries spread throughout the body in a similar way to blood vessels. The lymph vessels usually run parallel to the arteries and veins in the body. Lymph vessels and capillaries collect fluid from the spaces in between the cells, from all over the body, filter it and then return it back into the blood circulation system. Once the fluid passes into the lymphatic vessels, it is called lymph. The fluid is filtered by forcing it through lymph nodes. Lymph nodes help filter bacteria and other toxins from your body by trapping harmful organisms using specialised white blood cells (called lymphocytes), present in these nodes, to destroy them. The purified fluid, enriched with defence cells (infection-fighting cells), is distributed through the lymph vessels back into the body. Lymph vessels are equipped with one-way valves that act like gates to ensure lymph fluid only flows in one direction. The pressure (or squeezing) on the lymph vessels from muscle movement propels lymph through the lymph vessels.  

Therefore, the main function of the lymphatic system is to transport, and filter the fluid (lymph) collected from the spaces between the cells and have the overall capacity to manage both effectively.

Lymph fluid transport is aided by:

  • breathing
  • muscle contractions
  • pulsation in the arteries
  • external compression therapy (for example, manual lymphatic drainage, compression bandaging or graduated compression garments)

 

The defective lymphatic system / when it goes wrong

When the lymphatic system is damaged, or it hasn’t developed properly, it causes a disruption to the normal flow of fluid. The fluid cannot drain properly and excess fluid accumulates in the body's tissues causing a swelling (known as, lymphoedema). The swelling may be slight at first, possibly intermittent, and may reduce overnight with elevation. However, in time and without treatment, the swelling becomes more persistent and changes occur to the skin and tissues. The body's natural defence reaction is to send defence cells (infection-fighting cells) into the damaged area which additionally reinforce the blockage and interrupt fluid transport.

Lymphoedema patients are at higher risk of developing an infection. Lymphocytes cannot reach the parts of the body where infection occurs due to the swelling. The swelling, resulting from the lymphoedema, causes a distribution of the local immune system. This means the body may not be able to effectively fight invading bacteria.

When lymph fluid remains stagnant in the tissues (lymphostasis), the body interprets this excess protein as a foreign body and tries, as a protective mechanism, to separate this area. This can cause chronic inflammation and subsequently lead to fibrosis (a growth of connective tissue, similar to the formation of scar tissue). Fibrosis can feel hard and tight and makes it more difficult for the lymph fluid to be moved out of the area. It also increases the risk of infections (such as cellulitis or lymphangitis), and it can lead to the skin changing in appearance and texture.

The swelling mostly affects the limbs, although other areas of the body can be affected. In some cases, both arms or both legs may be affected at the same time.