Brain Res Rev
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According to the traditional hypothesis, the cerebrospinal fluid (CSF) is secreted inside the brain ventricles and flows unidirectionally along subarachnoid spaces to be absorbed into venous sinuses across arachnoid villi and/or via paraneural sheaths of nerves into lymphatics. However, according to recent investigations, it appears that interstitial fluid (ISF) and CSF are formed by water filtration across the walls of arterial capillaries in the central nervous system (CNS), while plasma osmolytes are sieved (retained) so that capillary osmotic counterpressure is generated, which is instrumental in ISF/CSF water absorption into venous capillaries and postcapillary venules. ⋯ Multidirectional distribution of substances inside CSF, as well as between CSF and ISF, is caused by to-and-fro pulsations of these fluids and their mixing. Absorption of CSF into venous sinuses and/or lymphatics under the physiological pressure should be of minor importance due to their minute surface area in comparison to the huge absorptive surface area of microvessels.