08/05/2026
Here's a little fact you might have heard before: Humans are around 70% water. About the same percentage as a sweet potato, incidentally. But what does that actually mean? Sure, there's blood, that accounts for some of it. And the lymphatic system has a fair amount too, sloshing around. There's water in each of our cells. But that doesn't add up to the full 70% - where is the rest of it?
In 2018, a scientific paper was published which gives a tantalising clue. The authors revealed for the first time that our 'interstitial spaces' - those gaps, between our bones and joints and all of our organs - spaces which are often somewhat sidelined in conventional anatomy - those spaces were full of a kind of soft, gel-like liquid. Flowing around the body. Bringing essential substances to where they're needed. Connecting all the disparate parts of us and communicating between them. They called this massive, fluid-filled system 'The Interstitium', and suggested that it might be a brand new, previously undiscovered organ.
This moist, fibrous network seems to be important, in ways we still don't quite understand. It seems to have a key role in so many of our body's essential functions, from wound repair, to the maintenance of our body-clocks, to the spread of cancer from one tissue to another. And it's everywhere.
Emily Knight takes a journey deep into the human body, into the ocean within us, the spaces in between the things we think of as 'us'. And discovers the way it flows, and the things that flow through it.
https://www.bbc.co.uk/programmes/m002zrqy
