Cytotoxic edema involves the cerebral cortex, whereas vasogenic edema is more pronounced in the white matter. Vasogenic edema is more important clinically than cytotoxic edema. Astrocytes are important for regulation of metabolic activities of neurons. They take up GABA and glutamate that are released at synaptic clefts and convert them to glutamine. Glutamine is then transferred to neurons and recycled into GABA and glutamate.
Astrocytes are also important for maintaining proper ionic balance in the extracellular fluid.
This process, which is called gliosis, is for the CNS what scarring is for extraneural tissues. Astrocytes participating in gliosis are referred to as reactive astrocytes . They have a large cytoplasmic mass, long, branching processes, and increased cytoplasmic filaments. Such astrocytes are also known as gemistocytic astrocytes from a Greek word that means to fill up. In acute metabolic disorders such as hepatic encephalopathy, hyperammonemia, and cerebral ischemia, astrocytes enlarge.