Which of the following does not promote multiple steps in the clotting pathway? a. platelet phospholipids, b. factor XI, c. thrombin, d. Ca²⁺.

Video transcript

Welcome back, everyone. Which of the following is a large plasma protein that forms a bridge between platelets and collagen. We have choice A thrombin, choice B, prothrombin, choice C. Von Willebrand Factor and Choice D fibrinogen. We're going to need to draw up an example of a blood vessel which I'll represent as a tube-like structure. And at a certain point, there is an exposed and damaged portion of the blood vessel where we want to include then the endothelium that lines the inner walls of our blood vessel. And at that broken portion of the blood vessel, it's going to have an exposure of the sub endothelial layer which I'll represent as purple, smaller lines. So we'll label that as the exposed subendothelial layer, we have our endothelium lining the inner walls of the blood vessel. And then of course, our blood vessel on the out side of everything. So recall that the endothelium helps regulate blood flow. And if it's now damaged within the blood vessel, we have again, the exposed subendothelial layer. Recall that collagen is contained here and recall that we have types 13 and four collagen and the collagen contained here upon disruption of the endothelium is now going to be exposed to blood. So now that blood flow is no longer being regulated properly. And so, in order to address this recall that there are platelet structures which I represent as circles present within the blood that are cells which play a vital role when it comes to damaged blood vessels. And that role is to adhere to the exposed collagen within the sub endothelial layer. Now under conditions of stress where now that blood vessel is damaged, there's high blood flow causing what we should recall as sheer stress which will prevent then the platelets from being able to adhere to the exposed collagen at the site of damage. And so what we need is then to show this protein that is present, I'll represent that as a square. This protein is called Von Willebrand factor will use VWFS shorthand recall that it's produced and released by endothelial cells. And so Bron Von Willo brand factor is used as a bridge to then allow for the platelets to bind to the collagen. And that's because Von Willebrand factor can respond to specific receptors on the platelets to then anchor them to the site of injury, which forms sort of like a platelet plug and that's going to initiate the formation of then a blood clot and that's going to ultimately help stop bleeding. Now, based on what we've outlined, looking at choice C, we do have Von Willo brand factor mentioned So let's place a check mark by choice. C Now looking at choice a thrombin recall that, well, thrombin is a part of the blood clotting cascade. It's going to be an enzyme responsible for converting fibrinogen, which recall is a soluble inactive protein into fibrin, which is an active insoluble protein which forms the basis of blood clots. So that is the essential role of thrombin. And we would rule out choice a for that reason because it has nothing to do with the platelets and collagen as far as forming a bridge. Now, we've got choice B, prothrombin recall that prothrombin is the precursor protein in the blood clotting cascade to form, then thrombin which is its active form. So prothrombin is an inactive precursor protein to thrombin. And for that reason, we would rule out choice B because it's not related to forming a bridge between the platelets and collagen. And last, we have D fibrinogen. And as we outlined in choice, a thrombin is used to aid in the conversion of fibrinogen an inactive protein to then an active protein called fibrin, which again, we said forms the basis of blood clots since it is an insoluble protein. So for that reason, we rule out choice D as well. And that confirms that choice C. Von Willo brand factor is going to be the final answer as the large plasma protein that forms a bridge between platelets and collagen. I hope this helped and let us know if you have any questions.