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Interstitial Fluid

Dr. Sumaiya Khan Apr 21, 2019
Interstitial fluid is a liquid which surrounds the cells in the body. It acts as a medium for intercellular communication, delivery of nutrients to the cells, and removal of metabolic waste.
The human body is made up of many cells. Each organ contains cells that are specialized either in their structure and/or function. These cells are connected to each other with the help of intercellular junctions. However, in between these cells, there is a solution that bathes the cells. This solution is known as interstitial fluid.
It can be defined as the main component of extracellular fluid which is found in interstitial tissue spaces. It is an important component of the body and in fact, on an average, a person has eleven liters of interstitial fluid. Following are some more details regarding the formation, composition, and the function of this fluid.


Whenever the heart pumps blood into the arteries, which supply this blood to various organs, it does so under pressure. Due to this hydrostatic pressure, it pushes water out of the capillaries. This differential water potential is established because the small solutes are able to drift past the capillary walls.
Due to this, there is osmosis, and so the water passes from a point of high concentration to a point of low concentration. This same osmotic pressure also eventually manages to push this water back into the circulatory system.
This pressure is different in different places of the body, like, the pressure is highest in arteries and lowest in veins, in direct correspondence to the pressure, rate, and direction of the flow of blood and the presence of solutes.


The basic composition of interstitial fluid is water, along with solutes like sugars, fatty acids, amino acids, salts, urea, white blood cells, etc. Thus, it contains nutrients as well as waste products. Although the basic composition of this fluid remains the same, it differs slightly depending on the region of the body where the fluid is present.
In fact, the composition of this fluid is very similar to the composition of lymph fluid, as lymphatic fluid is also considered to be interstitial fluid. However, this composition varies slightly depending on the location of the fluid like the lymphatic fluid will contain more of white blood cells so as to combat any kind of infection. 
Also, certain other types of interstitial fluid, like peritoneal fluid are present mostly for lubrication purposes, so this fluid is more clear and contains lesser cells.


There are many functions served by the interstitial fluid. Basically, this fluid is responsible for maintaining the homeostasis in the cell and in the body.
It also helps deliver nutrients to the cells and carry waste from the cells to other organs like the kidneys, from where it is eliminated. Also, this fluid may contain hormones which will reach the target organ via this fluid. It may even contain neurotransmitters.
There are certain diseases associated with this condition, like ideally, this fluid needs to be removed from cells and be put back into circulation.
If this fluid is not removed, then there is a build up of this fluid, which leads to swelling and a condition commonly known as elephantiasis, which is a severely disfiguring condition that leads to build up and swelling of the ankle and feet, which is exacerbated due to gravity.
Sometimes, the build up of fluid may even be due to obstruction of the flow of lymph, which may even affect the functioning of the entire lymphatic system. Thus, if there is a build up of this fluid, then it should be diagnosed and treated at the earliest.
Disclaimer: This is for informative purposes only, and should not be used as a replacement for expert medical advice.