====== Extracellular interstitial fluid ======
 

Extracellular [[interstitial fluid]] is a thin layer of fluid that surrounds the body's cells.

Although there is no [[lymphatic system]] in the [[central nervous system]] (CNS), there seems to be a mechanism to remove [[macromolecule]]s from the brain. [[Cerebrospinal fluid]] (CSF) and [[interstitial fluid]] (ISF) are thought to be parts of this [[pathway]], but the details are not known.

Since substance exchange occurs between the CNS extracellular interstitial fluid (ISF) and CSF, it is assumed that CSF serves as a sink for the removal of various metabolites out of the CNS by its unidirectional pulsatile flow and [[absorption]]
((Davson H, Welch K, Segal MB. The physiology and pathophysiology of the cerebrospinal fluid. 1st edition. Edinburgh: Churchill Livingstone; 1987.))
((Fishman AR. Cerebrospinal fluid in disease of the nervous system. Philadelphia: W B Saunders Co; 1991.))
((Irani DN. Cerebrospinal fluid in clinical practice. Philadelphia: Saunders Elsevier; 2009.))

see [[Cerebrospinal fluid physiology]].