Brain Extracellular Fluids

The composition of brain extracellular fluid is critical because changes in the ionic environment affect the electrical behavior of neurons and will disrupt function.

Three extracellular fluid compartments.

1. Blood Plasma

•        contained inside the vascular system (approximately 70 mL).

2. Interstitial Fluid

•        located outside the vascular system in contact  with neural cells and glia (approximately 250 mL). 

3. CSF ( Blood Cerebro-spinal Fluid )

•        located within the ventricular system and subarachnoid space (approximately 150 mL).  The composition of CSF must be carefully regulated. 

Each ventricle contains a CSF fluid. The circulation of CSF replaces the CSF volume approximately four times per day.

Functions of the CSF include:

• To act as a shock absorber to protect the brain from contact with the skull during movement.
• To assist in the maintenance of a constant internal environment in the CNS.
• To provide a route for removal of metabolites from the brain.