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Imagine a fierce white blood cell, ready to battle an invading bacteria, racing through the circulatory system…

Just as cars need a highway on which to travel in order for the drivers to reach their destinations, so do your cells need blood and lymphatic vessels so that your cells can reach their desired destination.

To help cells reach their desired destination they need a means by which they can travel quickly through the body. Just as a human paddles a boat down the rapids, racing with glee, your cells are able to happily float through the blood and lymphatic vessels if there are body fluids to carry them.

Different names are given to body fluids based on where they are found:

  • Blood is the fluid inside blood vessels. This fluid is  made up of red blood cells, white blood cells, platelets and plasma which is water inside the blood vessels.
  • Lymph is the fluid inside lymph vessels. This fluid is made up of water, salts, proteins (albumins, globulins and fibrinogen) and white blood cells.1
  • Tissue fluid (also known as interstitial fluid) is the fluid sitting in the tissue spaces. This fluid is similar to lymph. 

What is the circulatory system?

The cardiovascular system moves blood.

The lymphatic system moves lymph.

The circulatory system of the human body involves the cardiovascular and the lymphatic systems working together. Body fluid is transported through the blood, then into the tissues then into the lymphatics where it eventually returns into the blood.

Representation of how the lymphatic system and the cardiovascular system work together to transport body fluid.

What is lymph?

Lymph is from the latin word “lympha” which means “pure water or streams”.

Lymph simply refers to the fluid found in the lymphatic system and lymph vessels of the body.

There are two types of lymph fluid in the human body:

1. Lymph fluid that does not contain fat.

This type of fluid is clear. It is found inside most superficial lymph vessels such as in the tissues of the arms, legs, breast, genitals and face.

To illustrate what lymph fluid looks like, lets explore a blister. Fluid inside a blister is tissue fluid. This fluid is similar to lymph and is clear in colour. At this stage the fluid is known as tissue fluid, or interstitial fluid, as it has not been collected by the lymph vessels. In order for the fluid in the blister to escape it must be carried by the lymph vessels or alternatively it can escape through the skin, which is not ideal as the skin will be broken leaving it susceptible to infection.

Image of a common blister by FrazzmatazzCC BY-SA 3.0, via Wikimedia Commons.


2. Lymph fluid that contains fat.

This type of lymph is known as chyle. Chyle is found in the lymphatics of the digestive system which drain into the large lymphatics of the abdomen. The cisterna chyli is the most lower part of the thoracic duct – the biggest lymphatic vessel in the human body. This lymph vessel receives fatty chyle from the intestines and contributes to digestion via the transportation of fats within the human body.

It is the first type of non-fatty lymph fluid that causes the swelling most commonly seen in those living with lymphoedema and can result in swelling in the arms, legs, breast, genitals and face.

What is the lymphatic system?

The lymphatic system is a network of organs, lymph nodes, lymph ducts and lymph vessels that transport fluid from the tissues to the bloodstream. The lymph system is a major part of the body’s immune system.

Reference: Moore Jr JE, Bertram CD. Lymphatic system flows. Annual review of fluid mechanics. 2018 Jan;50:459.