- Lipid-soluble substances (C02 and 02) and H20 freely cross the blood-brain barrier and equilibrate between blood and CSF.
- Other substances are transported by carriers in the choroid plexus epithelium. They may be secreted from blood into the CSF or absorbed from the CSF into blood.
- Protein and cholesterol are excluded from the CSF because of their large molecular size.
- The composition of CSF is approximately the same as that of the interstitial fluid of the brain, but differs significantly from blood (Table 2-8).
- CSF can be sampled with a lumbar puncture.
Table 2-8. Comparison of Cerebrospinal Fluid (CSF) and Blood Concentrations
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