According to some scientists, the interstitium is the largest organ in the human body. That is a slightly controversial view, however, for reasons we’ll get into shortly.
The interstitium was only discovered in the last 10 years and most of us don’t even know that we have one.
So, what is it, where is it and what does it do?
Think of the interstitium as a network of channels that runs around and between our cells and tissues: a space between spaces.
These channels are filled with fluid and seem to have multiple roles in our bodies, including cushioning and supporting our tissues, transporting oxygen, nutrients and waste products, and playing a part in our immune systems.
Prior to 2018, this network was thought of simply as fluid between our cells – important, but not a distinct organ or organised network. Then, a team of researchers published an eye-opening paper that made biologists think again.
They used an advanced imaging technique called confocal laser endomicroscopy, which is a way of looking inside the body in real-time. The real-time element is important because it explains how we missed a significant part of human anatomy for so long.
When researchers take biopsies or perform dissections, they see a ‘collapsed’ version of the tissues they’re working with, because any fluids that were present have drained out in the lab setting.
Confocal laser endomicroscopy allows us to visualise our bodies functioning in three dimensions. When researchers used it to view tissues as diverse as our lungs, skin and digestive tract, they noticed that this in-between fluid was not travelling through compressed tissues.
Instead, they saw open, interconnected channels, supported by a scaffold of collagen and elastin fibres. It was a picture entirely missing from centuries of anatomy textbooks.
In the years since the interstitium’s discovery, there has been debate around the nature and function of it. It may serve as a kind of intracellular shock absorber, for example.
The channels drain off into lymph nodes so it’s likely that they play a role in the removal of waste tissue and possibly serve as a kind of communication highway through the body.
It may also be a mode of transport for white blood cells, when our body mounts an immune response or a route that cancer cells use to spread throughout the body. Other medical implications include it potentially playing a role in swelling and inflammation.
Ever since the 2018 paper, there has been a debate about whether the interstitium constitutes an organ in its own right. Its spongy structure and multifunctional nature are some of the reasons to grant it that status.
It’s also vast, covering as much as 20 per cent of the body’s volume, according to some estimates.
Others argue it’s not a distinct organ, but simply an improved picture of a network we knew was there all along – one of the many systems that the body uses to carry out its functions.
Either way, this is early science and researchers are only beginning to understand how the interstitium impacts our lives and whether it can be harnessed for new types of treatments and medicines.
This article is an answer to the question (asked by Joel Percival, Sutton Coldfield) 'What is the interstitium?'
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