This video, we're going to talk about vascular spasm, which is the first step of hemostasis, the process that helps to prevent and control bleeding after an injury. Vascular spasm refers to the immediate contraction, or the immediate vasoconstriction of damaged blood vessels to reduce the diameter of those damaged blood vessels, which helps to reduce the amount of blood flow to the damaged site, and that ultimately helps to reduce the amount of blood that is lost. Vascular spasm, or this contraction or vasoconstriction of the damaged blood vessel, is the result of the contraction of smooth muscle cells that are present in the walls of most blood vessels.
The contraction of those smooth muscle cells is initiated by chemicals that are released by either damaged endothelial cells that are present in the walls of all blood vessels, or those chemicals can actually be released by damaged smooth muscle cells themselves, or the contraction can be initiated by chemicals that are released by activated platelets. Now, vascular spasm, this contraction or vasoconstriction, is something that can occur continuously over a relatively large period of time. Several minutes, such as 20 to 30 minutes, up to several hours in some cases. This reduction or this contraction and the reduction of the size of the diameter reduces blood flow, reduces blood loss. That reduced blood loss for that extended period of time helps to buy sufficient amount of time for the next two steps of hemostasis to occur, which are platelet plug formation and blood coagulation, or blood clotting.
Notice, on the left-hand side down below, we're focusing in on the blood vessel before the injury, and so you can see this is how it might look. And then on the right side, we're focusing in on what the blood vessel looks like immediately after injury. Notice that here we have some damage to the blood vessel wall, and notice that some blood is actually escaping, and this person would actually be bleeding. Immediately after the injury, vascular spasm would occur. Vascular spasm is going to be contraction or the vasoconstriction of the damaged blood vessel. Notice here the arrows represent the constriction of the blood vessel walls. And, notice that the diameter is actually narrowing down, and that reduces the blood flow to the damaged site, which reduces how much blood is actually lost from the damaged site.
Again, vascular spasm can occur for long periods of time, and that helps to buy enough time for the next two steps of hemostasis to occur. This here concludes our brief lesson on vascular spasm. In our next video, we'll be able to talk more about the second step of hemostasis, which is platelet plug formation. So I'll see you all there.