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Figure 9 | Fluids and Barriers of the CNS

Figure 9

From: Mechanisms of fluid movement into, through and out of the brain: evaluation of the evidence

Figure 9

Possible schemes to explain rapid influx of markers via periarterial spaces: a) the glymphatic proposal based on Figure five of Iliff et al. [[143]], b) stirring or mixing and c) layered flow. In a) and c) there is preferential influx via the space between the arterial wall and the pial sheath (the inner periarterial space in Figure 6) while in b) convection back and forth, speeds up the rate of transfer of markers in both directions. Red lines represent pial membranes, grey lines the layer of glial end-feet or glia limitans, solid arrows are fluxes of markers carried or assisted by convection, dashed arrows are either by diffusion or assisted by convection and green arrows have been added as a reminder that fluid secreted by the blood-brain barrier contributes to the fluid in the parenchyma. The location of the pial barriers is based on Zhang et al.[23] (Figures 1d and 6). In c) the influx of fluid via the periarterial spaces may inflate the space of His providing a route for the return of fluid to the subpial space at the cortical surface and then to CSF in the subarachnoid space.

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