Cerebrospinal fluid
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Introduction
CSF bathes the brain and spinal cord, providing mechanical and metabolic buffering. CSF is an important waste management system due to its high rate of production, its circulation, and its free exchange.
CSF Production
Ventricles are filled with cerebrospinal fluid.
Fourth ventricle leads to the third ventricle via the cerebral aqueduct
medulla and pons
CSF and the Brain Extracellular Fluid
CSF is exchanged freely across the pial-glial membrane, which has intracellular gaps. It can also cross between ependymal cells, special glial cells which line the ventricles. Ependymal cells form gap junctions but do not have a tight epithelium.
As such, macromolecules and ions can pass through paracellular openings
CSF Absorption
CSF is absorbed in a number of places.
CSF enters the venous return system in the sagittal sinus through arachnoid granulations or villi, which extend through the dura. Pressure-sensitive one-way valves prevent CSF backflow.
Transcytosis may be the actual mechanism of absorption.
Increased intracranial pressure increases CSF absorption but not production, leading to a balancing of pressure.
Impairment of CSF absorption, which can occur fowwing arachniod villi damage during meningitis, can lead to increased intracranial pressure in a condition called normal pressure hydrocephalus.
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