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Astrocytes, or astroglia, are star-shaped glial cells within the brain which have many processes that envelope synapses made between neurons. Astrocytes have several functions including the biochemical support of the endothelial cells in forming the blood-brain barrier, provision of nutrients to nervous tissues and to form scar tissue during repair of the brain. The fluorescent image of astrocytes on the right is possible because astrocytes express glial fibrillary acidic protein (GFAP) which facilitates their identification.

Astrocytes, or astroglia, are star-shaped glial cells within the brain which have many processes that envelope synapses made between neurons. Astrocytes have several functions including the biochemical support of the endothelial cells in forming the blood-brain barrier, provision of nutrients to nervous tissues and to form scar tissue during repair of the brain. The fluorescent image of astrocytes on the right is possible because astrocytes express glial fibrillary acidic protein (GFAP) which facilitates their identification.

[[Image:astrocyte.jpg|thumb|right|150px|Astrocyte (immunofluorescence staining). Image courtesy of Alliance Européenne Dana pour le Cerveau (EDAB)]]

[[Image:astrocyte.jpg|thumb|right|150px|Astrocyte (immunofluorescence staining). Image courtesy of Alliance Européenne Dana pour le Cerveau (EDAB)]]

 

 

Another key role of astrocytes is within the brain where they play an important structural role as well as performing the roles described above. Astrocytes are involved in the physical structuring of the brain and the interplay between astrocytes and mesenchymal cells is important in sculpting [[Forebrain_-_Anatomy_%26_Physiology#Cerebral_Cortex|sulci]] in development. Astrocytes also delineate the  CNS from the PNS by creating the CNS-PNS interface. The cells cover the surface of the brain and where this occurs the astrocytes' surface is coated by a basal lamina.

 

** Astrocytes are involved in the physical structuring of the brain:

Where astocytes are involved in repair within the brain they take over from fibroblasts to play an important role in abscess formation, as it is difficult to induce fibrosis within the CNS. It is due to this role that astrocytes are the only differentiated CNS cell that retains the ability to divide.

*** Interplay between astrocytes and mesenchymal cells is important in sculpting sulci in development.

*** Astrocytes delineate the  CNS by creating the CNS-PNS interface.

*** The cells cover the surface of the brain.

Within the metabolic role that astrocytes play within the brain, it has been found that they may control glucose levels and provide lactate for neurone for energy production. The lactate is believed to be produced via the lactate shuttle mechanism. Astrocytes also have high levels of antioxidants, such as glutathione peroxidase which protects the neurons from damage by reactive oxygen species.

**** In this situation, the astrocytes' surface is coated by a basal lamina.

*** Astrocytes take over from fibroblasts to play an important role in abscess formation, as it is difficult to induce fibrosis in the CNS.

*** Astrocytes are the only differentiated CNS cell that retains the ability to divide.

Perhaps one of the most important roles that is undertaken by astrocytes is that of the '''blood brain barrier (BBB)'''. It was originally thought that the astrocyte "end-feet" that encircle adjacent endothelial cells within the BBB aided in the maintenance of the blood-brain barrier. However, the tight junctions and basal lamina of the endothelial cells are now considered to play a more substantial role in maintaining the barrier and within this astrocytes play a key role.

** Astrocytes may control glucose levels and provide lactate for neurone for energy production

*** This is by the lactate shuttle mechanism.

** Astrocytes have high levels of antioxidants, such as glutathione peroxidase.

*** This protects neurons from damage by reactive oxygen species.

* '''Blood brain barrier'''

** It was originally thought that the astrocyte end-feet encircling endothelial cells aided in the maintenance of the blood-brain barrier.

***  The tight junctions and basal lamina of the endothelial cells are now considered to play a more substantial role in maintaining the barrier.

* '''Transmitter reuptake'''

* '''Transmitter reuptake'''

** Astrocytes:

** Astrocytes: