Blood Coagulation and Wound Healing Video

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  • 0:06 Hemostasis and…
  • 1:51 Platelets
  • 3:09 Thromboxane A2
  • 5:11 Coagulation Cascade
  • 6:39 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

When your blood vessels suffer damage, your body follows a sequence of events to promote blood clotting. In this lesson, you will learn about coagulation cascade and important clotting factors involved in wound healing.

Hemostasis and Clotting Factors

We previously learned that the body works hard to regulate and control blood flow. But if a blood vessel gets injured, the body must jump into action to avoid the loss of too much blood. In this lesson, you will learn about the events that happen immediately after a wound to control bleeding.

Almost immediately after you suffer a cut, your body reacts by initiating a series of events that happen one after another until the bleeding stops. Hemostasis is a term used to describe the stoppage of bleeding. This is an easy term to recall if you remember that 'heme' is the Greek word for 'blood' and 'stasis' is the Greek word for 'halt.' So hemostasis can be literally thought of as the halting of blood or the stoppage of bleeding.

This series of events depends on specific proteins called clotting factors. Clotting factors are substances in your blood that act in sequence to stop bleeding by forming a clot. There are many clotting factors, and they often interact with each other. Many of them are named using Roman numerals, such as factor XII, factor XI, factor X, and so on, while others go by more common names, such as fibrinogen (factor I), prothrombin (factor II), or tissue factor (factor III). We'll learn more about these clotting factors later in the lesson.

These clotting factors depend on vitamin K to function properly. Vitamin K is required for the synthesis of clotting factors, and it's so important to the blood-clotting process that it sometimes goes by the nickname 'the clotting vitamin.' Without it, you could experience excessive bleeding, so vitamin K is important to get in your diet, and it's found in such foods as green leafy vegetables, broccoli, cauliflower, and cabbage. So there's another good reason for you to eat your vegetables.


When a blood vessel wall is damaged, collagen fibers from within the wall are exposed. These exposed fibers become a place for platelets to cling to. Platelets are irregular-shaped bodies that help the clotting process by sticking to the lining of the blood vessels. These odd-shaped fragments of cells are normally found floating around your blood along with your red blood cells, kind of minding their own business. But when the cells that line the blood vessels get injured, they release chemicals that cause the platelets to kick into action and become sticky. What we see is layer upon layer of platelets laying down over the wound, somewhat like dirty 'plates' piling up in a sink.

Platelets attach to exposed collagen fibers from a damaged blood vessel, helping to stop blood flow.

Platelets are like the first responder to a site of an emergency, but platelets can't plug the hole alone. They need some help. This is where we start to see some of the clotting factors that we talked about earlier. One in particular, called fibrinogen, is an inactive clotting factor that helps bind the platelets to form a clot. These inactive clotting factors act as little cross-links, attaching the adjacent platelets to each other. So, in wound healing, platelets take a lot of the glory for being the first ones to the scene, but without their support team, fibrinogen, they would not be able to properly hold together.

Thromboxane A2

So we're starting to see how a wound can get plugged up with platelets. But the thing is, there are not enough platelets in the immediate area of the wound to properly plug the hole. So platelets solve this problem by calling for help. How do platelets call for help? They do this by releasing tiny granules that send out chemical signals. These chemicals attract more platelets to the wound site, which helps build the plug. But these chemicals do more than just recruit more platelets. For instance, one important chemical in this process is called thromboxane A2. Thromboxane A2 is a product of activated platelets that promotes the collection of more platelets and vasoconstriction. Vasoconstriction is an important component of wound-healing, and it's one of the very first steps in healing a damaged blood vessel. It's this vasoconstriction that initially slows the flow of blood through the vessels and decreases the amount of blood lost.

Aspirin blocks the chemical thromboxane A2, leading to prolonged bleeding.
Aspirin and Thromboxane A2

So thromboxane A2 is a platelet-recruiter and a vasoconstrictor, making it an important player in blood clotting. Interestingly, though, aspirin is an antithrombotic agent. We know that 'anti' means 'against' and 'thrombo' means 'blood clot,' so aspirin is a drug that is against the formation of a blood clot because it blocks the synthesis of thromboxane A2. Without the thromboxane A2, the platelets can't keep coming to the injured site as quickly, so aspirin can lead to more or prolonged bleeding.

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