a. Define hemostasis. b. List the three major phases of coagulation. Explain what initiates each phase and what the phase accomplishes. c. In what general way do the intrinsic and extrinsic mechanisms of clotting differ? d. Which ion is essential to virtually all stages of coagulation?

Video transcript

Welcome back, everyone which of the following factors does not trigger the intrinsic clotting pathway. We've got choice. A tissue factor B, glass C activated platelets or D collagen. So recall that when it comes to clotting pathways, we have either the intrinsic, so either the intrinsic clotting pathway or we have then the extrinsic clotting pathway. So let's show an example of things that can trigger the intrinsic clotting pathway. The first trigger we can show is damaged or damage done to the inner blood vessel lining. So we're going to draw a sketch to show that we'll have a blood vessel represented by this horizontal rectangular structure. And we're going to show a break in the blood vessel recall that blood vessels are lined with an endothelial layer. So the lining is the endothelium lining on the inner portion of the blood vessel. And then we've got because of that break in the blood vessel. Now, an exposure of the sub endothelial layer, which I will represent as these purple horizontal lines where we're called that contained in the sub endothelial layer is collagen and specifically, it would be types 13 and type four collagen. So with this break in the blood vessel, we now have an exposure of the sub endothelial layer and the collagen it contains and now that exposes the collagen to the blood flow that is surrounding the blood vessel. So that exposure is going to trigger an intrinsic clotting pathway which will lead to a series of enzymatic reactions where ultimately a fibrin clot should form in order to address this internal damage of the blood vessel. A second trigger for the intrinsic clotting pathway is going to be contact with negative charged surfaces. So we can think of an example being a test tube which contains blood on the inside and the test tube will say is made of glass. So the test tube made of glass has a negative charge and the blood that it is contained with is in contact with that negative charge of the glass that is going to initiate a series of reactions in the blood, which will follow an intrinsic pathway which would lead to clot formation. And so that's why typically when blood is contained in glass tubes in medical settings or in scientific settings, there are anti coagulants used in the blood collection tubes, which are made of things like sodium citrate or heparin to prevent the blood from clotting. Now, let's consider the extrinsic clotting pathway just as before we're going to sketch a very basic blood vessel represented by a horizontal line that is rectangular and we're not going to show a break in this blood vessel. It's going to be undamaged so far and above the blood vessel, we're going to roughly draw muscle tissue fibers as these curved lines to represent the muscle tissue as a whole which surrounds the blood vessel. Recall that above the muscle tissue will be a layer of fat and then above that layer of fat is going to be an even thicker layer of skin. Now, we're going to show a break in each of these layers because ultimately, there's going to be damage caused by a cut, exposing blood flow through this cut, which is going to represent a site of trauma. And that is going to trigger an extrinsic pathway where there will be a release of factor three known as tissue factor caused by this external trauma, damaging the external portion of the blood vessel along with the tissues that are surrounding it and the upper layers of the skin. So we can note down that the extrinsic pathway the trigger here is going to be the release of tissue factor due to external blood vessel trauma and its surrounding tissues. So now that we have outlined a summary of the intrinsic and extrinsic clotting pathways based on our answer choices. A trigger that will not apply to the intrinsic clotting pathway. We're going to rule out choice A because tissue factor in choice A would correspond as we outlined to the extrinsic pathway. We can also rule out choice B which is glass because glass is too general of a saying it's typically just going to be any artificial substance with a negative charge and that negative charge in contact with something like blood is going to initiate an intrinsic clotting pathway. So glass, we would rule out and sorry correction. So we actually will not rule out choice B because as we outlined, it is the glass that has the negative charge that initiates the intrinsic clotting pathway when in contact with blood, that triggers the reactions of the blood to coagulate. However, we're going to place a check mark by choice. A since we need to choose for our final answer, a factor that will not trigger the intrinsic clotting pathway. So tissue factor because it describes the extrinsic clotting pathway trigger, we would consider as an answer. Choice B we would rule out because glass is an trigger for the intrinsic clotting pathway. We can also rule out choice C and D because activated platelets and collagen are also triggers of the intrinsic clotting pathway. So that allows us to confirm that a tissue factor which is a trigger for the extrinsic clotting pathway when external trauma exposes the surrounding tissues of a blood vessel to blood flow and damage upon the release of tissue factor or factor three. And that entire process is not applicable to the intrinsic clotting pathway. So, a tissue factor is our final answer. I hope this made sense and let us know if you have any questions.