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Current time:0:00Total duration:6:25

Video transcript

hi everyone I want to start off by talking about Mary Mary likes to play soccer and she was at one of her games when and she was running really fast she scored a goal and then she tripped and fell and scraped her knee and then she started to bleed now normally our bodies want to make sure that our blood which is flows flows through our blood vessels stays in our body but if we have an injury that allows blood to leak out of the blood vessel and out of our body we want to make sure we can stop that and we do that through a process called hemostasis and it's through hemostasis that we create this clot and this clot allows the blood to the bleeding to stop it stabilizes the injury in the blood vessel and it allow gives the blood vessel time to heal now let's take a look at exactly what's going on in Mary's knee and exactly how we make this clot so here we have a blood vessel and in our blood vessel we have our blood in our blood we have many different types of cells one of the most important ones is our red blood cell that carries oxygen all over to all our tissues in our body and in this blood vessel we make sure that blood is flowing smoothly in one direction did you know that if we were to line up all of our blood vessels the total length of our blood vessels would come out to about 150,000 kilometers which is about 93 thousand miles this is the same distance as if you were to travel around the earth a little bit less than four times so you can see we have a lot of work our blood vessels have a lot of work to do and one of the cells that helps with this are the cells that line the inner wall of the blood vessel the cells that communicate with the blood these cells are called endothelial cells and it's it's these cells that allow the blood to flow smoothly and these are the cells that communicate with the blood whenever there's been an injury and hemostasis needs to begin now let's take a look at Mary's mean she scraped your knee so let's a break in her skin let's say this is her skin and she also caused damage to the blood vessel underneath so let me erase this let me cause some damage to the blood vessel and so you can see blood that should be flowing in this direction now can come out of the blood vessel and out of the skin in this direction we want to stop this and the way we stop this is through hemostasis there are two stages to hemostasis the first stage is primary hemostasis and this begins immediately after there's been an injury and what happens is the endothelial cells at that site of injury begin to secrete proteins and send signal and the send signals to the blood that there's been an injury and in our blood we have platelets these platelets are made in the bone marrow just like red blood cells and their purpose is to respond to injured blood vessels and I drew them as squares but they're actually about this small compared to red blood cell the reason I drew squares I want to make a note of what they carry inside of them they carry these sacs or granules that carry molecules and proteins that are necessary for hemostasis so they store them and they're ready for use whenever needed and so what happens is the endothelial cells secrete these proteins and send a signal to the platelets to come to that site of injury and then a sequence of events happens with the platelets then I won't go into details here but it allows the platelets to stick to that side of injury they get activated they change shape they release what they have inside and then they start clumping together and call more platelets and cause more platelets to clump there as well and what we end up with is what we call a platelet plug and this is the first step of stopping any bleeding but this is still kind of weak and we need to make this stronger and that's where secondary hemostasis comes into play in secondary hemostasis we make this platelet plug stronger with the protein called fibrin and vibrant does is it lays over and links up on top of this platelet plug and makes it tighter and sturdier it's like tying a knot in order to prevent it from getting loose you double knot it or triple knot it and this is exactly what vibrant is doing but fibrin doesn't float in our blood as fibrin it carries around an extra piece of protein and when it has this extra piece of protein it's called fibrinogen so we need a way of getting fibrin from fibrinogen and the way we do that is with this family of proteins called coagulation factors and I'm drawing them all in one color but there are several different types of coagulation factors and the injured blood vessel will send signals to these coagulation factors to get activated and once one gets activated it will activate another and activate another and activate another and then ultimately that extra protein on fibrinogen will get cut off and that will allow fibrin to link up on the platelet plug and make it stronger this sequence of activation of coagulation factors is what we call the coagulation cascade I won't go into the details here either but it's key it's just key to remember that in secondary hemostasis we make this platelet plug stronger by getting fibrin from fibrinogen through the coagulation cascade and it's with this fibrin mesh over the platelet plug that we create this clot and it's this clot that stops bleeding allows blood flow to continue through the blood vessel and allows the blood vessel to heal