so you get a cut and you start bleeding but after a little while the bleeding stops and that stopping of the flow of blood is called hemostasis my name is leslie samuel and hemostasis is what you're gonna learn about in this video so let's do it [Music] [Applause] when you get a cut this causes damage to the walls of the blood vessels in that area as a result of that blood is going to escape through the damaged blood vessel and that's what you experience as bleeding now if you just keep on bleeding for too long that's eventually going to result in anemia this causes a whole host of other issues that come along with it as we discussed in the video on red blood cell disorders now you can check that video out for more details so we have to prevent that from happening and we want the tissue to actually heal now this hemostasis involves three processes the first is vascular spasm the second is platelet plug formation and the third is coagulation let's break these down individually first let's deal with vascular spasm this is also called vasoconstriction if we look at the structure of the walls of our blood vessels we see that the middle layer contains smooth muscle now anytime you see muscle you can know that contraction can happen in this case in response to the damage of the blood vessel the smooth muscle layers will actually start contracting this is called vascular spasms here's why this happens when there's a cut there are pain receptors they release chemicals in that local area also the cells that are lining the inner layer of the blood vessel wall will release chemicals those chemicals will cause the smooth muscle to contract and that action will help them to restrict the flow of blood it's like if you have a hose and you squeeze the hose that limits the flow of water it's the same thing here so that's the first step vascular spasms let's basically slow down the flow of blood then there's the formation of the platelet plug in the last video we spoke about platelets and how they play a significant role in hemostasis that's a great introduction to what we're talking about here and you can check that video out but essentially we have these platelets that are in the blood and they're freely traveling through the blood vessels for moments just like this well when there's damage to the blood vessel it exposes the underlying connective tissue and collagen fibers that's normally in the walls of those blood vessels and as the platelets are passing by minding their own business they get activated and change their shape they also will release granules and the result is that they become kind of spiked and sticky so they clump together around the damaged tissue to form what's called a platelet plug this entire process is helped by a glycoprotein that's found in the blood called von willebrand factor it helps to stabilize the platelet plug this is kind of like a temporary internal band-aid that's helping to stop the flow of blood until we can have something more permanent and what's also cool is that as the plug forms the platelets themselves will release other substances that help the process even more they release adp adenosine diphosphate this helps to attract even more platelets to the site of injury they release serotonin which has various functions but in this situation it stimulates and helps to maintain the vasoconstriction we spoke about earlier some other substances that are released are things like prostaglandins and phospholipids they help to maintain vasoconstriction as well but they also help to activate other clotting factors and we'll talk about that in a sec and for the third and final process we have coagulation also known as clotting we're forming a blood clot yay now this is a process that involves a complex cascade of events that involves a bunch of clotting factors the goal of this process is to form a fibrin mesh that holds the platelet plug in place so that the healing can take place as efficiently as possible here's a simplified look at how this happens i mentioned earlier that there's a complex cascade of events in that cascades there are two pathways an intrinsic pathway and an extrinsic pathway they both involve various clotting factors the intrinsic pathway gets activated as a result of the damage to the wall of the blood vessel hence the name intrinsic it's a pathway that's within the blood vessel the extrinsic pathway happens as a result of damage to the extravascular cells those that are not a part of the blood vessels they're outside the blood vessels hence the name extrinsic now both of those pathways lead to a common pathway and here's the important part well it's all important but the key thing here the main goal is that in the common pathway there's an inactive enzyme called prothrombin that gets converted to the active enzyme thrombin and once this thrombin is active it converts fibrinogen which is soluble and inactive into fibrin which is insoluble and active the fibrin strands will form that fibrin mesh that we spoke about earlier that holds everything in place so that healing can happen so ultimately for hemostasis to happen first we want to slow down the flow of blood and the vascular spasms accomplish this then we want to get the platelet plug formation and lastly coagulation resulting in the vibrant mesh holding everything together and that's it for this video but if you're curious about blood types and the physiology behind all that it's really cool you want to check it out check out the next video and i'll see you over there peace