hi everybody dr. Mikey in this video we're gonna take a look at blood clotting also known as hemostasis now hemostasis has three steps we look at step one two and three and it occurs when you have damage to a blood vessel wall so you know that there's blood moving through this blood vessel and the walls of our blood vessels are filled with the smooth muscle so the fill-in the first step when you have damage to the blood vessel wall what happens is it stimulates the smooth muscle in this wall to constrict this is also termed a vascular spasm and this is the very first step in hemostasis now why do we have a vascular spasm why do we want the smooth muscle in the blood vessel wall to constrict it's because it's going to limit the amount of blood going through therefore limiting the amount of blood that may be left from that damage in the wall so that's the first step now that in the second step what you're going to find is because we've damaged the blood vessel wall there's not just smooth muscle there's also connective tissue right and connective tissue can include collagen so when you damage this blood vessel wall you have collagen fibers now being exposed and these collagen fibers are like little flags to another cell component that's moving through the blood vessel not just the red blood cells but the platelets and platelets are fragments of cells called megakaryocytes that are produced in the bone marrow and platelets will recognize what they're going to do is they're going to come past and they're going to recognize this collagen that's been exposed now something interesting happens here this second step is known as the platelet plug so let's write that up the platelet plug this happens within 30 within 30 to 60 seconds right of this damage to the blood vessel wall so the collagen has been exposed platelets coming past they say it they stick to it now here's what happens when the platelets stick to the collagen the platelets release something so what are the platelets release right the platelets release something called prothrombin activator now prothrombin activator released from the platelets when they bind to this collagen prothrombin activator activates prothrombin and what prothrombin is is it something that's produced in the liver and also requires vitamin K so it's vitamin K dependent for its production and prothrombin is part of this coagulation phase which is the next phase prothrombin turns into thrombin when prothrombin activator comes across it and what thrombin is is their molecular scissors that cut proteins and the protein that thrombin cuts in this case is going to be fibrinogen and it cuts fibrinogen into fibrin and this is what we want we want fibrin because what fibrin is is there these protein threads right so let's just go through this quickly platelets stick to the exposed collagen from the damaged blood vessel wall all right platelets then get activated and they release something called prothrombin activator prothrombin activator turns prothrombin which is floating through right and produced in the liver and is vitamin K dependant into something called thrombin now thrombin will turn fibrinogen which is always floating through into something called fibrin so now we also have fibrin at the site of the platelet plug and what this fibrin does is in addition to the platelets that are now accumulating at this damaged site we now have all these fibrin fibers and what they do is they reinforce the clot and this is the third phase known as the coagulation phase and now what we have is a blood vessel wall that is now no longer bleeding or losing blood and then we have the remodeling process occurring where we start to fix this damaged blood vessel wall by putting in that connective tissue which is help mediated by fibrin so these are the three phases of hemostasis also known as blood clotting