Glymphatic system

The glymphatic system, glymphatic clearance pathway, or paravascular system is an organ system for removing metabolic waste from the vertebrate central nervous system (CNS). In mammals, cerebrospinal fluid flows into the paravascular space around cerebral arteries, where it mixes with interstitial fluid and solutes within the brain parenchyma, and exits via the cerebral venous paravascular spaces into the subarachnoid space. The pathway consists of a para-arterial influx mechanism for cerebrospinal fluid driven primarily by arterial pulsation. This "massages" the low-pressure cerebrospinal fluid into the denser brain parenchyma. During sleep, flow of cerebrospinal fluid is regulated by changes in parenchyma resistance due to expansion and contraction of the extracellular space. Clearance of soluble proteins, metabolites, and excess extracellular fluid is accomplished through convective bulk flow, facilitated by astrocytic aquaporin 4 water channels. The term "glymphatic system" was coined to indicate its dependence upon glial cells and the similarity of its functions to those of the peripheral lymphatic system.