What Is a Thrombus? - Definition & Formation

Instructor: Virginia Rawls

Virginia has a master' degree in Education and a bachelors in Sports Medicine/athletic Training

The word 'thrombus' is the technical term for a blood clot. A thrombus can form anywhere in the circulatory system. This lesson will explain what a thrombus is and how it is formed.

The Circulatory System

The term thrombus is a fancy word for a blood clot. But what is a blood clot? Let's first review the circulatory system to better understand what a thrombus is and how it is formed.

The circulatory system, also referred to as the cardiovascular system, transports blood throughout the body. As blood travels it delivers blood cells, oxygen, carbon dioxide, water, hormones, and other nutrients. At the same time, blood also transports damaged blood cells, carbon dioxide, and other waste to parts of the body where they can be removed. Blood is a liquid that flows easily through the circulatory system.

The circulatory system is made up of the heart, blood vessels (arteries, veins, capillaries), and blood. These three components work like a well oiled machine to keep your body running. The heart pumps blood so that is can reach all of the tissues (bone, muscle, organs, etc.) in our body. The arteries deliver blood to the tissues while the veins remove used blood from the tissues.

The circulatory system
circulatory system

Think of the heart, blood vessels, and blood like the subway system in a major city. The electricity that runs the subway cars is like the heart. The subway tracks are the blood vessels and the cars are the blood. The people who get on and off the subway cars are the nutrients, blood cells, and other components of blood that are getting transported through the system.

What is a Thrombus?

Blood normally travels easily through the arteries and veins. However, there are times when blood cells can begin to attach to the walls of the heart, arteries, or veins. When blood cells attach to the walls, this can cause other blood cells to stick to them as well, causing a blockage. This blockage is called a thrombus. A thrombus can completely or partially block a blood vessel. The picture below shows a thrombus in the lower leg.

A thrombus

Let's compare this to a traffic accident on a highway. Normally, traffic moves quickly and freely on the roadway. When an accident occurs, the cars involved stop in the lane that they are in. Due to the accident, other drivers have to slow down to maneuver around the damaged cars. Sometimes other cars end up hitting the original cars in the accident, causing more lanes to shut down. Now the backup becomes severe. Only one lane of traffic can get through, and it moves very slowly. This is exactly what happens when a thrombus forms in our body.

A thrombus that forms and then breaks away from the wall of a blood vessel is called an embolus. An embolus is a thrombus that moves, or floats, through the circulatory system. An embolus is a very serious and life-threatening condition.

If a blood vessel is blocked it can keep oxygen from reaching the tissues served by that vessel. When oxygen is not reaching tissues like it should, it is called ischemia. Ischemia can lead to tissue death. A thrombus can also lead to heart attacks, strokes, and damage surrounding tissues. This picture depicts a thrombus that could potentially cause a stroke.

A thrombus that could potentially cause a stroke

How Does a Thrombus Form?

A thrombus can form if there is an injury to a blood vessel, if blood sits still for a long period of time, or if a build-up of cholesterol in the blood occurs.

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