why does venous block cause infarction?

[scilearner]

Hi guys,

I know this is a simple question. But when an artery is blocked it is easier to understand because, less oxygen goes to tissue so, necrosis of tissue. But when a vein is blocked, only the draining is affected, the arteries are still able to supply oxygen, but why does necrosis still occur. I'm assuming it is because when a vein is blocked, it leads to congestion, increased back pressure, which makes it difficult for arterial blood to come and perfuse tissue. Just asked to clarify (I know this is probably a pretty obvious stupid question, but I like to get it clarified). Thanks

 

While we are at it, if u know something about this, please tell me

Does the pathogenesis of cerebral venous infarction differ considerably from the pathogenesis of cerebral arterial ischemic infarction. Why does a haemorrhagic infarct occur in cerbral venous infarction.

Edited May 31, 2013 by scilearner

[MagnusMallard]

Veins carry blood back to the right ventricle, via the right atrium; this deoxygenated blood is pumped to the lungs via the pulmonary artery. This blood is then re-oxygenated and pumped to the left ventricle, which in turn pumps oxygenated blood to the rest of the body. When a vein (or veins) are blocked, the blood supply is restricted not only to the left ventricle, but also to the right ventricle; as a result, the oxygenated blood supply will be insufficient. This results in necrosis. Veins and arteries are part of the circulation, and if any of them are blocked, the blood supply is restricted. Basically, the veins 'feed' blood to the left ventricle via the lungs. The amount of oxygenated blood supplied to the body is affected by the performance of the veins, because blood is 'recycled' (red blood cells have a life span of around 3-4 months, and it takes minutes for them to circulate).

 

Cerebral venous infarction and cerebral arterial infarction are caused by numerous factors, and obviously result in blockage, or partial blockage of the arteries - which supply nutrients and blood to the brain - and/or the veins, which take away toxic waste products of cells' metabolism. Both involve the restriction of blood flow, which could be caused by atheroma deposition, vasoconstriction, aneurysms (and therefore blood leakage), blood viscosity etc.

Blood clots/thrombi can form in the cerebral veins which lead down to the jugular; this causes venous infarction - the veins become congested and may eventually cause a cerebral haemorrhage. Again, the infarction is typically the result of the coagulating blood.