  Interstitial connective tissues are one of the four basic types of animal
tissue and continuously distributed throughout the body. Illustrated by the
movements of the micron-sized particles across the defined tissue boundaries
and the continuously distributions of the fluorescently stained hyaluronic acid
within the fibrous tissues around blood vessels and nerves, the authors of this
paper suggested that interstitial fluid (ISF) is not fixed locally but would
flow through fibrous matrices for a long-distance, even between more distant
parts of the body. However,the fluid-filled interstitial spaces are similar
with the interstitial tissue channel, lacking a distinct spatial structure for
"free" interstitial fluid flow, which might be the key to comprehend the
whereabouts and directions of a systemic fluid flow and circulation.
