Stroke: what is it?
A stroke happens when blood going to the brain is interrupted. Blood is carried to the brain by blood vessels called arteries. Blood may stop moving through an artery because the artery is blocked, or because the artery breaks or bursts.
When blood stops flowing, the brain does not receive the oxygen it needs. Brain cells in the affected area die and the brain can become permanently damaged. Brain cells usually die within one hour from the beginning of the stroke. However, sometimes brain cells can survive for a few hours after the stroke starts.
There are 2 main ways a stroke can happen. Either there is a blood clot or plaque that blocks a blood vessel in the brain, or a blood vessel in the brain breaks or ruptures.
Ischaemic stroke
A stroke that is caused by a blocked artery is called an ischaemic stroke.
In everyday life, blood clotting is beneficial. When you are bleeding from a wound, blood clots work to slow and eventually stop the bleeding. In the case of a stroke, however, blood clots are dangerous because they can block arteries and cut off blood flow. An ischaemic stroke is caused when a blood clot blocks a blood vessel in the brain.
There are two ways that a blood-clot stroke can occur. An embolic stroke forms somewhere in the body and travels through the bloodstream to the brain. A thrombotic stroke occurs when clots form around pieces of the blood vessel deposits, and can grow to completely block the blood vessel.
Haemorrhagic stroke
A stroke that is caused by a bleed in the brain is called a haemorrhagic stroke.
A haemorrhagic stroke is caused when a blood vessel in the brain breaks or ‘erupts’. When this happens, blood leaks into the brain stopping the delivery of oxygen and nutrients. Haemorrhagic stroke can be caused by a number of disorders which affect the blood vessels, including long-standing high blood pressure and cerebral aneurysms. There are 2 types of haemorrhagic stroke: a subarachnoid haemorrhage and an intracerebral haemorrhage. These 2 terms refer to areas of the brain where the stroke has occurred.
In a subarachnoid haemorrhage, bleeding occurs under the thin, delicate membrane surrounding the brain.
An intracerebral haemorrhage involves bleeding within the brain tissue itself.
Last Reviewed: 08 January 2008
