CSF pressure is mainly regulated by:(AIIMS May 2012, May 2011)

Ans. b. Rate of CSF absorption (Ref: Ganong 24/603, 23/e p571; Guyton 12/e p747, 11/765)CSF pressure is mainly regulated by rate of CSF absorption. (AIIMS May 2011, November 2008, May 2008 Repeat)Cerebrospinal Fluid (CSF)CSF is produced by choroid plexuses, absorbed by the arachnoid villiQ.Volume of CSF: 150 mLQRate of CSF production: 550 mL/dayQ (CSF turns over 3.7 times/day)Rate 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 points)CSF formationQ50-70% is formed by choroids plexusQ, remaining CSF formed around blood vessel and ventricular wallsQVolume150 mlQRate of CSF formation550ml/day (2.3 ml/hr or 0.38 ml/min)QRate of CSF turnoverApprox. 3 time /dayQSpecific gravity1.006-1.007QCSF pressure70-180 mm of H2O (8-10 mm of Hg)Ion with maximum CSF/plasma ratioMg2+QMinimum CSF/plasma 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 mg/dlQSugar40- 70 mg/dlQChlorides720-750 mg/dlQCell/mm3Lymphocytes (0-5)QDLC60-70% lymphocytes, 30-40% monocytes, 0% (None) neutrophilsQ