<prompt> CSF pressure is mainly regulated by:AIIMS May 2012, May 2011Rate of CSF formationRate of CSF absorptionCerebral blood flowVenous pressure  <response>: Ans. b. Rate of CSF absorption Ref: Ganong 24603, 23e p571; Guyton 12e p747, 11765CSF pressure is mainly regulated by rate of CSF absorption. AIIMS May 2011, November 2008, May 2008 RepeatCerebrospinal Fluid CSFCSF is produced by choroid plexuses, absorbed by the arachnoid villiQ.Volume of CSF: 150 mLQRate of CSF production: 550 mLdayQ CSF turns over 3.7 timesdayRate of CSF formation is independent of intra-ventricular pressureQ.Absorption of CSF is proportional to its pressure. At 112 mm CSF pressure, filtration and absorption are equal. Whereas, below 68 mm CSF absorption stops.CSF Important pointsCSF formationQ50-70 is formed by choroids plexusQ, remaining CSF formed around blood vessel and ventricular wallsQVolume150 mlQRate of CSF formation550mlday 2.3 mlhr or 0.38 mlminQRate of CSF turnoverApprox. 3 time dayQSpecific gravity1.006-1.007QCSF pressure70-180 mm of H2O 8-10 mm of HgIon with maximum CSFplasma ratioMg2QMinimum CSFplasma ratioCholesterol and ProteinQEqual CSF plasma ratio is withOsmolalityQAll ve ions Na, K, Ca2 are more in plasma except Mg2 which is more in CSFQAll -ve ions Cl- HCO3- are more in CSFQ.CSF ConstituentsAppearanceClear colorlessProteins20 - 40 mgdlQSugar40- 70 mgdlQChlorides720-750 mgdlQCellmm3Lymphocytes 0-5QDLC60-70 lymphocytes, 30-40 monocytes, 0 None neutrophilsQ 