What is a stroke? – Circulatory system diseases

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What is a stroke?

Our brains are so complex, and the way they work is still such a mystery. It is not surprising that most of us go about our day without giving them much of a second thought. That all changes if you have a stroke.

A stroke is an interruption of the blood flow within your brain that causes the death of brain cells. There are two ways this can happen:

  • A blood clot can block a blood vessel in the brain causing an ischemic stroke. If the clot dissolves quickly and the blockage is only temporary, it is called a transient ischemic attack (TIA) or mini stroke.
  • A blood vessel can leak or burst inside your brain causing a brain bleed. If this happens, you have had a hemorrhagic stroke.

What keeps your brain working?

Most of your brain consists of neurons, or specialized nerve cells that connect together into networks that send and receive messages. They coordinate everything that our bodies do. However, in order to function properly, your brain needs a constant supply of oxygen and nutrients—and a lot of them. Oxygen and nutrients travel in your blood and are delivered to your brain cells via two pairs of major arteries called the carotid and vertebral arteries. These major arteries branch into a dense network of small blood vessels that covers the surface and thread their way throughout your brain tissue ensuring that every cell is well supplied.
How your brain is organized and what can go wrong

Your brain is arranged into three parts, the brain stem, cerebellum and cerebrum. Different areas of the brain are generally responsible for different functions and actions:
Brain stem: this connects your brain to the top of your spine and controls lots of basic functions including your heart rate and blood pressure, breathing, consciousness, sleeping and eating.
Cerebellum: this is attached to the back of the brain stem. It helps control your coordination and balance, and fine tunes your muscle movements (motor function).
Cerebrum: this is the largest part of the brain and is divided into two halves or hemispheres, which are further divided into four lobes, the frontal, parietal, temporal, and occipital lobe. The right side of the cerebrum controls the left side of your body and vice versa.
The frontal lobe controls movement, and executive function, which is our ability to make good or bad decisions, make plans, and manage time. It is also involved in forming memories. The parietal lobe processes what we are seeing, hearing, smelling and touching, which lets us locate exactly where we are physically, and gives us hand-eye coordination.
The temporal lobe controls hearing and memory, recognition of faces and languages, and is important for storing long-term memories.
The occipital lobe processes the signals from our eyes and is primarily responsible for most things to do with sight.
A stroke can happen in any part of the brain. Around eight out of ten strokes are caused by a blockage due to a clot (ischemic), while two out of ten are caused by a bleed (hemorrhagic).

Ischemic strokes are more common. There are two types, thrombotic and embolic strokes. A thrombotic stroke occurs when the blood clot has formed in one of the major arteries leading to the brain, while an embolic stroke is when a blood clot forms somewhere else in the body, travels around your body in your bloodstream and then lodges in your brain. Loose blood clots are usually linked to atherosclerosis, a buildup of plaque (a combination of fatty materials, calcium and scar tissue), on the inside walls of your arteries, which narrows them, and interferes with or blocks the flow of blood. Blood clots form when a plaque ruptures.
Hemorrhagic strokes are less common, but are more deadly. Uncontrolled bleeding can flood an area of the brain, causing localized pressure and swelling that damages or kills the brain cells. Hemorrhagic strokes can also cause a shortage of oxygen and nutrient delivery beyond the leak. Bleeding may occur at the surface of your brain, just under your skull, or from a burst artery deep within your brain. High blood pressure and/or defects in your arteries are usually to blame for a brain bleed. The common defects include aneurysms, which are weak areas in the blood vessel wall that fill with blood, bulge out like a little balloon, and can burst, particularly if you have high blood pressure, and malformations of blood vessels that are usually present at birth.
Loss of blood flow due to a blockage, even for very short periods of time, can be enough to cause the neurons in that area to die due to a lack of oxygen and nutrients. That said, every stroke is different and sometimes your brain can compensate to some extent, by shifting the brain function of the damaged part of your brain to the corresponding area on the undamaged side of your brain. This means the damage caused by either type of stroke may be permanent but could only be temporary. Signs and symptoms caused by a mini-stroke will usually last less than an hour, and generally do not do permanent damage.
Signs and symptoms that you are having a stroke


Usually the signs and symptoms of a stroke come on suddenly and include one or more of the following:

  • Your face may droop unnaturally on one side.
  • You may not be able to raise your arm on one side.
  • You may feel confused and have trouble understanding what people are saying.
  • Your speech may sound slurred and jumbled when you talk
  • You may have difficulty seeing with one or both eyes.

Because different parts of your brain control different activities, a wide range of signs and symptoms can develop depending on where the damage is done:
Area of damage Possible effects
Brain stem A stroke in the brain stem is uncommon, but often fatal. Brain stem strokes may cause problems with breathing, heart function, balance and coordination, chewing, swallowing, speaking, and seeing, as well as weakness and paralysis on both sides of your body.
Cerebellum Strokes in the cerebellum are less common than in the cerebrum (the large part of the brain), but can cause severe effects including problems with balance and coordination, dizziness, headaches, nausea and vomiting.
Cerebrum – Left hemisphere Strokes in the left hemisphere typically cause weakness or paralysis on the right side of your body, and cognitive problems including difficulties with reading, talking and thinking, and learning and remembering new information.
Cerebrum – Right hemisphere Strokes in the right hemisphere typically cause problems with vision, depth perception, short-term memory loss, and judgement, as well as weakness or paralysis on the left side, and a tendency to ignore things on your left side including your own left arm and leg.
Are you at increased risk of having a stroke?

There are things that you can’t control such as your gender, family history and age, that affect the likelihood of whether or not you will have a stroke. The risk is higher if you are male. Strokes also seem to run in families, so your risk goes up if one of your immediate relatives has had a stroke. Your risk for strokes also increases as you get older. Then there are other risk factors that increase your chances of having a stroke. These are called “modifiable” risk factors, which means they can potentially be treated or controlled. These risk factors tend to be interconnected and linked to lifestyle. The most important one for any kind of stroke is high blood pressure, which can damage and weaken your arteries so that they clog or burst more easily. High blood pressure is responsible for over 50% of strokes.
Other important risk factors include atrial fibrillation, which means you an irregular heartbeat, high cholesterol, diabetes, physical inactivity and smoking. The more risk factors you have, the more likely you are to have a stroke.
How likely are you to have a stroke?

Every year, almost 17 million people worldwide have a stroke and almost 6 million people die because of it.
Stroke is responsible for almost 10% of all deaths worldwide and is the number two killer after heart disease.
Death from stroke is highest in Eastern Europe and Russia, and South East Asia, and is generally more common in lower income countries.
Stroke in young and middle-aged people is happening more often than ever before, with most strokes occurring in people younger than 75 years old.
Unfortunately, about 5 million people worldwide are living with permanent disabilities because of stroke.
How can you avoid a stroke?

Your doctor can help you to reduce your risk of stroke by helping you tackle the risk factors that you can do something about. As a first step this will likely involve changes to your diet and exercise, which can help in so many ways. In addition to simply making you feel better, eating more healthily and exercising more often can help lower your blood pressure and cholesterol levels, prevent diabetes, and help you to lose weight. If lifestyle changes are not enough, your doctor may prescribe medications to help control some of these factors. Other ways to prevent a stroke include drinking in moderation, quitting smoking and reducing the stresses in your life. Your doctor can also give you help with all of these if you need it.
Diagnosing and treating a stroke

A stroke is a medical emergency! The faster you get medical treatment the better.
If you have signs or symptoms of a stroke, you need to get a proper diagnosis and treatment as soon as possible to minimize damage to your brain. You may need several tests to help diagnose what has gone wrong and which parts of your brain have been affected, as well as to guide your treatment.
Your doctor will likely start with a physical examination, followed by a computerized tomography (CT) scan, to decide whether or not you are having a stroke and what kind it is. Other tests that can provide your doctor with useful information include magnetic resonance imaging (MRI), which helps visualize any brain tissue damage, an angiography that examines blood flow through the brain, blood and urine tests, an echocardiogram that shows how well the valves of you heart are working and the size of your heart chambers, an electroencephalogram (ECG) that checks the electrical activity of your heart, and a neurological exam to check how your brain function has been affected by the stroke.
Treating an ischemic stroke – if the CT scan confirms you are having an ischemic stroke, your doctor will most likely give you a clot busting drug called tissue plasminogen activator as soon as possible. This drug works by dissolving the clot, which restores the blood flow in your brain, and which may reduce the damage. Sometimes your doctors will try to physically break up and remove the clot, although this is much less common.
Treating a hemorrhagic stroke – your doctor will want to find the source of the bleed and try to control it, so as to reduce the pressure and any damage that it may cause. You may need surgery to do this and to repair any blood vessel damage.
After you recover from the initial emergency, your doctors will want to treat your risk factors, with lifestyle modifications and medicines if necessary.
Consider the following:

Even though mini-strokes do not usually cause permanent brain damage, don’t just shrug it off. Why do we say that? A mini-stroke should really be considered a warning that something is going wrong. You can think of a mini-stroke as getting lucky because the blood clot quickly dissolved on its own. However, there’s no way to predict that is what will happen when another clot forms. While for many people there is no warning mini-stroke before a full stroke, if you do get one, there is a good chance that you will have a full stroke within the next 3 months. So, take it seriously! Go see your doctor to find out why it happened and to get treatment in order to prevent a full stroke from occurring .

You can read more about health and medicine at Khan Academy.


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