What Are Platelets? - Definition, Function & Normal Range

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  • 0:01 What Are Platelets?
  • 1:15 Function of Platelets
  • 3:18 Normal & Abnormal…
  • 4:20 Lesson Summary
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Lesson Transcript
Instructor: Wendy McDougal

Wendy has taught high school Biology and has a master's degree in education.

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.

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.

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