Platelets are tiny cell fragments that circulate through our bloodstream. Their role is to help stop bleeding when there is an injury to our body. Learn more about the importance of platelets, and take a short quiz at the end.

What Are Platelets?

Remember the last time you cut yourself? You can recall the sharp stab of pain, and the sight of blood slowly oozing out of the wound. As you reach for a bandage, you are probably hoping to minimize the mess of blood. But is your mind racing, trying to figure out how and when you will stop bleeding? Probably not, because you know that your body will take care of that for you. The reason we don’t bleed to death every time we are cut is due largely to particles in our blood called platelets.

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Platelets are tiny cell fragments that are found within our blood. They originate in the bone marrow as pinched-off pieces of larger cells. Platelets are neither smooth nor round, but are shaped more like paper that has been ripped into tiny bits. They spend much of their time cruising through the bloodstream alongside their red and white blood cell counterparts.

The primary responsibility of the platelets is to stop the bleeding when there is an injury to the body. A barrier called a blood clot must be formed to seal the wound. Just like a leaking pipe must be plugged, a damaged blood vessel must be blocked so that there is not excessive blood loss. But how do the platelets accomplish this task?

Function of Platelets

Let’s go back to the scenario in which you cut yourself. You can see that your skin has been broken, and blood is escaping through the opening. Clearly there has been damage to some blood vessels, since you are bleeding. What you cannot see is that an emergency signal has been sent out in your bloodstream, like a dispatcher sending out first responders. This is when the platelets spring into action.

When the cut occurs, signals are sent through the bloodstream notifying cells of the trauma. Platelets in the blood release chemicals that notify other platelets nearby to become activated, or sticky. Once activated, platelets change shape by growing small tentacles. This helps them to stick together.

At the same time, other clotting factors are at work. A protein in the blood called fibrinogen has become active as well. It is now called fibrin, and as its name suggests, it produces fibers. These strands cover the wound and create a web of sorts. It is a similar situation to hairs clogging a drain. Now less blood can escape, but the platelets still need to finish their job.

The activated platelets continue to arrive on the scene through the bloodstream. They stick together and become caught in the web of fibrin. Red blood cells become trapped as well. Again, imagine that drain clogged with hair. If you added bits of paper to that drain on top of the hair, it would most certainly create a totally blocked drain.

The sticky platelets are now accomplishing their goal of sealing up the wound. As they continue to clump together in the fibrin, they form a complete barrier that keeps blood from escaping. This barrier is known as a blood clot.

Now that the blood clot has been formed and there is no more blood loss, the damaged skin and blood vessels can regenerate. The clot becomes a sturdy scab that will last until the tissue is fully healed. Eventually the scab falls off, and hopefully, there is little evidence of an injury.

Normal and Abnormal Range of Platelets

A healthy individual has somewhere between 150,000 and 450,000 platelets per microliter of blood. There can be serious health implications for those who fall outside of this normal range. Too many platelets in the blood is called thrombocytosis. Too few platelets is known as thrombocytopenia.

For people who have thrombocytosis, the major health issue is spontaneous blood clots in the arms and legs. This is a dangerous condition, as it can lead to heart attack and stroke. In this situation, a patient can have a procedure in which some blood is removed and platelets are taken out, thus lowering the total count.

Individuals with thrombocytopenia run the risk of too much bleeding. Bruising easily and bleeding frequently from the gums and nose are other symptoms that are experienced. It is much more dangerous for people with this condition to become injured, so they must live life more carefully than others.

Lesson Summary

Platelets are small cell fragments found circulating throughout the bloodstream. Their primary role is to help form blood clots when blood vessels are damaged. When a blood vessel is broken, platelets are activated to become sticky. They travel to the site of damage and clump together in a web of fibrin to form a blood clot, a barrier that prevents further blood loss. The normal range of platelets is 150,000 to 450,000 platelets per microliter of blood. Individuals who have an abnormal number of platelets can have serious health issues, such as a heart attack or stroke for people who have thrombocytosis, or too many platelets in the blood, and too much bleeding for people who have thrombocytopenia, or too few platelets in the blood.

About Platelets

Platelets are what form blood clots during an injury
Diagram of a blood clot
  • Platelets are small cell fragments responsible for forming blood clots when trauma to your blood vessels occur
  • Platelets become sticky when activated and become caught in a web of fibrin to stop the flow of blood at the trauma site
  • Too many platelets can cause spontaneous blood clots and too few can mean the risk of too much bleeding from injuries

Learning Outcomes

When you are finished, you should be able to:

  • State the purpose of platelets in the blood
  • Explain how platelets form blood clots
  • Discuss the conditions related to platelet counts