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Fig. 1 | Fluids and Barriers of the CNS

Fig. 1

From: Analysis of convective and diffusive transport in the brain interstitium

Fig. 1

Illustration of movement of fluid and solutes in brain tissue between interstitial tissue (parenchyma) and perivascular space surrounding penetrating vasculature. Green arrows indicate fluid transport, whether by diffusion, dispersion, or convection and diffusion has not been established. The figure shows movement of fluid along the periarterial space into the interstitium and out along the perivenous space. This is one proposed theory, and other evidence suggests periarterial and perivenous transport in the opposite direction of blood flow. Purple indicates interstitial solutes; solutes exit the interstitial space through gaps in the astrocytic endfeet to either to the perivenous or periarterial space, where they are cleared to primary para-venous drainage pathways or the CSF. Although the interstitial space looks essentially open in this illustration, it is crowded with cells and extracellular matrix where both fluid and solutes move along a tortuous path in a restricted extracellular liquid volume that comprises approximately 20% of the total volume

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