a. How is clot overgrowth usually prevented? b. List two conditions that may lead to unnecessary (and undesirable) clot formation.

Video transcript

Welcome back, everyone. Which of the following plasma proteins binds to thrombin and inactivates it. We have choice. A tissue factor B, antithrombin, three C, prothrombin and D tissue plasminogen activator. We're going to start by recalling our blood coagulation cascade. We're going to represent it as a very general flow chart. And we're gonna start by recalling that coagulation is a term that describes when blood goes from its liquid phase to its gel phase. And coagulation is important as a part of homeostasis to help make bleeding stop when necessary. So we're going to start our flow chart with a very primary protein of this cascade, which we should recall as prothrombin. Recall that prothrombin is also known as Factor two and is produced by the liver and in its role as prothrombin is an inactive protein. Now, prothrombin with the help of the enzyme prothrombin ase is converted to its active form as the thrombin protein. So that is the second tier of our flow chart where an arrow from prothrombin, we should draw to thrombin and then from thrombin, there is an interaction with a soluble blood protein known as fibrinogen. And thrombin is able to convert fibrinogen to what we would observe as fibrin clots. And so these fibrin clots are made up of fibrin, which is an insoluble protein, which is why there are blood clots. So fibrin strands are going to link together in order to form a mesh like structure and these mesh like structures will bind and form the framework of fibrin blood clots to prevent bleeding. Another important aspect of the blood coagulation cascade. We're going to label as antithrombin three. So let's draw an arrow from antithrombin three, going toward thrombin where we're going to draw then a crossed circle to in a shorthand way signify that antithrombin three is a protein that inactivates thrombin and antithrombin three is very important because it is a natural coagulant, sorry, natural anti coagulant. So what that means is that it helps the blood from clotting too much. And antithrombin three is a very important protein because it can inactivate several enzymes of the blood coagulation cascade, including what we represented by thrombin as well as another enzyme known as factor X A and several other clotting factors. So, in reference to our pumped, we would place a check mark by choice B antithrombin three. Since again, it does inactivate the protein thrombin from allowing the blood coagulation cascade to continue to form fibrin clots. Now, considering choice a tissue factor, we're going to rule it out because recall that tissue factor is a protein that initiates blood clotting or rather we'll say blood coagulation pathways where there are a total of two. So it initiates one of the two blood coagulation pathways and it does so via factor seven, which is another protein. Let's also rule out choice c prothrombin, which we should recognize as a precursor to the protein thrombin. So it's a precursor protein and it only gets converted to thrombin, as we stated with the help of the enzyme prothrombin ase. So now we can also rule out choice d tissue plasminogen activator, which we should recall is a part of the fibrinolysis system which prevents excessive blood blood clotting. And so it represents an enzyme that promotes the conversion of plasminogen two plasmin which helps with breaking down those blood clots. So overall, the key thing is that our answer we're left with is choice B antithrombin three which confirms the only correctly listed protein out of our options that will bind to thromb during anti or during its role as an anti coagulant in order to prevent excessive formation of blood clots. So again, it's going to inactivate thrombin. And so this is our final answer. I hope this made sense and let us know if you have any questions.