  Fluid in interstitial spaces accounts for ~20% of an adult body weight. Does
it circulate around the body like vascular circulations besides a diffusive and
short-ranged transport? This bold conjecture has been debated for decades. As a
conventional physiological concept, interstitial space was the space between
cells and a micron-sized space. Fluid in interstitial spaces is thought to be
entrapped within interstitial matrix. However, our serial data have further
defined an interfacial transport zone on a solid fiber of interstitial matrix.
Within this fine space that is probably nanosized, fluid can transport along a
fiber under a driving power. Since 2006, our imaging data from volunteers and
cadavers have revealed a long-distance extravascular pathway for interstitial
fluid flow, comprising four types of anatomic distributions at least. The
framework of each extravascular pathway contains the longitudinally assembled
and oriented fibers, working as a fibrous guiderail for fluid flow.
Interestingly, our data showed that the movement of fluid in a fibrous pathway
is in response to a dynamic driving source and named as dynamotaxis. By
analysis of some representative studies and our experimental results, a
hypothesis of interstitial fluid circulatory system is proposed.
