What happens in a stroke, exactly?

What is it?

A stroke happens when insufficient blood flow to the brain leads to cell death.There are two main types of stroke: ischemic, due to a lack of blood flow, and hemorrhagic, due to bleeding inside the brain. The symptoms of a stroke vary depending on which part of the brain is affected, but they typically start quickly and can include things like  an inability to move or feel on one side of the body, problems with speaking and understanding the speech of others, feeling like the world is spinning, and a loss of vision.

In 2013, 6.9 million people had an ischemic stroke while 3.4 million people had a hemorrhagic stroke. Strokes account for about 12% of all deaths. About half of stroke victims live less than a year after it. It is most common in older people. The stroke rates in developed countries have decreased during the last years, while in developing countries they have been increasing.

What causes it?

High blood pressure is the main risk factor. Others include smoking, obesity, high cholesterol, and diabetes.

What happens during it?

Our cells need energy for practically all their functions. We get this energy from food – it is stored in the bonds of molecules like glucose. Our cells break the molecules down to release the energy, and this process requires oxygen. Many of our cells, like muscle cells, don’t need a constant supply of glucose in the blood because they can store their own bigger molecules from which they can release energy if there isn’t enough glucose around. For our brain cells, however, glucose is the only source of energy they can use. This is why our brain needs a constant supply of blood to keep it going. The cells need it both for the oxygen and for the glucose. Being deprived from blood for just 60-90 seconds is enough to stop brain cells from functioning. After a few hours they are irreversibly damaged and may die.

An ischemic stroke can happen either when blood clots form in the vessels in the brain, or when they form elsewhere in the body but travel to the brain. Less blood means less energy, and less energy means less ability to maintain vital functions. One particularly damaging result of this is the release of the excitatory neurotransmitter glutamate. Normally, glutamate is carried back inside neurons by certain carrier molecules that work because the concentrations of ions are different between the two sides of the cell membrane. These concentration differences are maintained through pumping the ions to their side of the membrane. This pumping requires energy, and when there isn’t any, the concentration differences start to evaporate. This leads to loads of glutamate being released to the space between neurons. When the glutamate molecules bind to the other neurons, a reaction series begins which eventually leads to the cell’s own enzymes breaking down it’s building blocks. A shortage of oxygen also leads to the production of dangerously reactive substances, which destroy the tissue through reacting with practically anything that comes their way.

How can it be treated?

Timing is everything in the case of a stroke. The sooner the blood flow is returned to normal, the fewer cells die. In an ischemic stroke the primary focus is on removing the clot: this can be done with medications or surgically. This does not improve the chances of survival, but if done within the first few hours, it will make the stroke’s effects less disabling. The immediate treatment of those with a hemorrhagic stroke depends largely on the individual case. Blood pressure can be controlled, and sometimes the blood can be removed surgically.

After a stroke people have to regain the skills they need in everyday life, and often they have to redefine what a normal life means to them and learn how to cope with that. This is a long process. Ideally, this would partly take place in a stroke unit where there is staff with specific experience of treating people who have experienced a stroke. While every stroke is different and so is every treatment plan, the cornerstones of stroke rehabilitation are physical therapy, occupational therapy and speech-language pathology.



Source: en.wikipedia.org/wiki/Stroke



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