Causes of Blood Clots in the Brain

Instructor: Adrianne Baron

Adrianne has a master's degree in cancer biology and has taught high school and college biology.

This lesson is going to cover the two types of blood clots that may be in the brain. We will also look at the main causes of blood clots in the brain and how they lead to blood clot formation.

Blood Clots

The blood vessels in our body act a lot like a highway system. Our blood uses this highway system to transport blood cells, proteins, nutrients, and gases throughout the body just like cars use a highway system to transport people and goods.

We all like it when the highway system is wide open and traffic is flowing smoothly. We have all had those days when we get on the highway and traffic is moving very slowly. As more cars and trucks get to the area where traffic is moving slowly, they end up getting bunched up together and none of them can move. This is similar to something that happens in our blood highway system.

When our blood slows down, the blood cells and proteins within our blood begin to bunch up together and they eventually form one big clump, which we refer to as a blood clot. Now, there are times when a blood clot is beneficial, such as when it happens to stop bleeding after we get cut or scraped. However, some other instances of blood clots forming are about as beneficial as being stuck in traffic in your car!

We'll discuss this more later, but let's first understand the two types of blood clots. One is a thrombus, a stationary blood clot, and the other is an embolus, a blood clot that forms somewhere in the body and then enters the bloodstream to flow through the body.

Thrombus and embolus are the two types of blood clots
Diagram of a thrombus and embolus

Causes of Blood Clots in the Brain

Blood clots are able to form in any blood vessel anywhere in the body. They can cause problems anywhere that they form, however, there are some places in the body where blood clots are more problematic. One place is the brain. But what causes blood clots in the brain?

The first reason that a thrombus forms in the brain is because blood is flowing too slowly into or through the brain. Slow-moving blood will clot. Blood should flow fast enough that it doesn't clump together, but slow enough that it can exchange gases and nutrients with the body. Think about the minimum and maximum speed limits for the highway. They ensure we don't go too fast or too slow. In the brain, this can happen due to blood vessels becoming narrow from the build-up of plaque and the inflammation that occurs due to this build-up, which is a condition that we call atherosclerosis.

Narrowing of a blood vessel can cause blood clots
Diagram of atherosclerosis

Another cause of a thrombus in the brain is when there is an injury to a blood vessel in the brain. You will remember that blood clots form in order to stop bleeding. So, if a blood vessel is cut, a blood clot will form so the blood vessel doesn't bleed out onto the brain.

Blood clots may also occur in the brain because there is an accumulation of the proteins that cause blood to clot flowing in the blood. This makes the blood more prone to clot, even when it is flowing at the normal speed, because the clotting proteins will begin to stick to each other and then stick to blood cells. This will eventually form a full blood clot.

Some people suffer from a condition known as deep vein thrombosis, which is a condition where blood clots form in the veins in the inner part of the arms and/or legs. The thrombus may become loose from the vein where it formed and become an embolus that flows to the brain.

The last reason why there may be blood clots in the brain is because there is something wrong with the heart. Any time our hearts are not pumping blood as they should, the blood will flow slower than it is supposed to. As we already know from this lesson, blood that flows too slowly will form blood clots. In this instance, the problem with the heart could cause a thrombus to form in the brain, or an embolus may flow into the brain from somewhere else that is also affected by the heart not pumping blood effectively.

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