Download Hemostasis

Hemostasis
Pronunciation at: http://www.merriam-webster.com/dictionary/hemostasis
Objectives:
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Describe the blood-clotting process.
Understand how hemostasis is involved in both open cuts and in bruising.
Name and describe some conditions that can result from improper blood clotting.
Prior Knowledge:
 Basic knowledge of components of blood.
We have all cut ourselves at one time or another and just like this leaky hose, when a blood vessel is
damaged, blood escapes. I am sure you already understand how important blood is to keeping you alive
and you realize you can die if you lose too much blood. Remember, you only have about 5 liters so your
body must have some way of stopping blood loss. In this lesson you will learn about hemostasis, the
blood clotting process your body uses to minimize blood loss.
As you are aware, the basic components are blood are plasma, erythrocytes (red blood cells), leukocytes
(white blood cells), and platelets. It is these cell fragments called platelets that play a major role in
hemostasis or blood clotting.
First, let’s talk about an open cut, whereby an object has punctured the skin and damaged the wall of a
blood vessel to the point where the blood is escaping. This is similar to the image of the hose at the
beginning of this lesson. Our bodies are much different than the hose in that they have the ability to
respond to this damage.
The hose will just continue to leak until someone either turns off the water or quickly patches the
damaged area. However, our bodies very quickly begin a series of reactions that stop the blood flow
following the cut. Initially, the damaged blood vessel shrinks down in size to help limit blood loss in a
process called vasoconstriction. Next is where the cell fragments called platelets come into play. The
platelets that are always circulating in your blood immediately become sticky and begin adhering to the
opening in the blood vessel forming what is call the platelet plug. The platelet plug is a rather quick
response, but not a very permanent one. Again, it helps limit blood loss, but it is easily disrupted. Within
the plasma portion of your blood there are many different blood protein clotting factors along with calcium
ions. These clotting factors and calcium ions are important in initiating a process called coagulation
whereby your body begins producing some long hair-like fibers call fibrin. These fibrin strands are the
basis for the formation of an insoluble clot. This happens when the stands of fibrin begin to from a mesh
or type of netting that adheres to the inside of the platelet plug. This mesh is like a screen that has holes
so small that the erythrocytes or red blood cells can no longer escape. Instead get caught in the screen
and begin plugging up the hole. The image below shows erythrocytes caught up in the fibrin mesh. As
detailed as this process seems, this all happens rather quickly and normal blood will form a clot within 3-6
minutes. The red color that you normally see in a scab is simply those trapped red erythrocytes. We all
know that eventually the wound will heal and the scab will fall off.
Here is a nice youtube video giving a visual representation of the process:
https://www.youtube.com/watch?v=--bZUeb83uU
http://classes.midlandstech.com/carterp/Courses/bio211/chap17/chap17.htm
What about bruising then? How is the process any different? Well, actually it really isn’t much different
except that in a bruising situation the skin is not punctured, but more likely damaged by a blunt object.
The blood vessel is still broken and the components of blood are leaked into the dermal layer. You will
see that the bruise may be swollen and reddish-purple in color immediately after the injury. This is
because of those erythrocytes that are leaking and forming the clot. After time, the bruise will be more of
a blue or black color and then later as your body heals by breaking down these red blood cells, you may
notice that it the bruise turns a green or yellow color and eventually fades away.
There are two main medical conditions that can result if a person does not undergo the process of
hemostasis properly. Undesirable clotting within unbroken blood vessels is called thrombus and can
become very serious if the blockage is in a vessel that is serving a major organ like the brain or the heart.
After understanding the process of hemostasis I am sure you can imagine how the process would be
disrupted if a person has a platelet deficiency or lacks clotting factors in the blood. This could potentially
cause unwarranted and/or excessive bleeding or bruising. This condition is called hemophilia.
Hemophilia is an X-linked genetic disorder commonly called “bleeder’s disease” and is passed down from
parents to children.
The series of reactions that stop blood flow following an injury is called: Hemostasis
The formation of an insoluble clot during hemostasis is termed: Coagulation
Blood normally clots in approximately 3-6 minutes
Which one of the following represents the proper sequence of hemostasis: vascular constriction, platelet
plug formation and coagulation
Hemophilia is a condition that impedes the clotting of blood. In this sentence, what does “impedes”
mean? Prevents
What might happen if your body did not break down red blood cells? Bruises could remain swollen for a
very long time.
Bruises are caused by blood vessels rupturing. What is the best example of a rupture? Water balloon
bursting.
Scientists believe that bruising has a genetic component. What does that mean? People can inherit a
tendency to bruise from their parents
Place the following events in sequence: A) A bruise turns red and purple; B) A bruise turns green and
yellow; C) A bruise turns black and blue ACB