Changes

===VASOGENIC OEDEMA===

===VASOGENIC OEDEMA===

*The BBB breaks down in many pathological situations, e.g around brain tumours and when there is inflammation in the CNS.  

This BBB defect causes the BBB to break down in many pathological situations, e.g around brain tumours and when there is inflammation in the CNS. When this happens protein rich fluid spreads through the extracellular space of the brain, and is termed vasogenic oedema and since there are no lymphatic channels in the CNS, the excess fluid flows down pressure gradients, making its way to white matter and eventually to the ventricles. The presence of protein rich fluid causes astrocytes and microglial cells to react, causing astrocyte hypertrophy, swelling and upregulate many molecules. Microglia express MHC-2 molecules and take up plasma proteins. The presence of extra fluid in the extracellular space results in an increase in brain volume.

*When this happens protein rich fluid spreads through the extracellular space of the brain, and is termed vasogenic oedema, since there are no lymphatic channels in the CNS, the excess fluid flows down pressure gradients, making its way to white matter and eventually to the ventricles.

*The presence of protein rich fluid causes astrocytes and microglial cells to react, i.e astrocytes hypertrophy, swell, upregulate many molecules and may divide.  

*Microglia express MHC-2 molecules and take up plasma proteins.  

'''The presence of extra fluid in the extracellular space results in an increase in brain volume.'''

 

===CYTOTOXIC OEDEMA===

===CYTOTOXIC OEDEMA===

*It is important to distinguish the brain swelling which results from the presence of plasma in the extracellular space from the brain swelling that occurs as a consequence of cell swelling.  

It is important to distinguish the brain swelling which results from the presence of plasma in the extracellular space from the brain swelling that occurs as a consequence of cell swelling. Accumulation of fluid within cells, ''cytotoxic oedema'' is a common manifestation of many neurotoxic situations. It usually affects specific cells, or even parts of cells with the location being a reflection of the metabolic process being blocked by the neurotoxin:

*Accumulation of fluid within cells, ''cytotoxic oedema'' is a common manifestation of many neurotoxic situations.  

*Hexochlorophene and tri-ethyl tin cause fluid to accumulate in myelin sheaths

*It usually affects specific cells, or even parts of cells, the location being a reflection of the metabolic process being blocked by the neurotoxin:

*Cyanide caused swelling of axons

**Hexochlorophene and tri-ethyl tin cause fluid to accumulate in myelin sheaths

*Interfering with energy generation causes swelling of astrocytes.

**Cyanide caused swelling of axons

**Interfering with energy generation causes swelling of astrocytes.

<blockquote>'''CLINICAL LINKER:''' The distinction between cytotoxic and vasogenic oedema is important clinically when one is trying to decrease brain volume using hyperosmolar agents since one can only decrease brain volume with these agents when the BBB is intact.</blockquote>

<blockquote>'''CLINICAL LINKER:''' The distinction between cytotoxic and vasogenic oedema is important clinically when one is trying to decrease brain volume using hyperosmolar agents since one can only decrease brain volume with these agents when the BBB is intact.</blockquote>