Video Transcript
What is the role of thromboplastin
in the process of blood clotting? (A) To catalyze the conversion of
soluble fibrinogen into insoluble fibrin. (B) To form a net to trap red blood
cells that aggregate into a clot. (C) To initiate the conversion of
the protein prothrombin into the enzyme thrombin. Or (D) to initiate the release of
calcium ions to encourage the aggregation of blood cells.
Blood clotting is the process in
which blood coagulates or forms a thickened mass. If our blood didn’t clot, we could
lose fatal volumes of blood from every little cut or scrape. This question is asking us about
the role of thromboplastin, which is one of the components involved in the mechanism
of blood clotting.
Let’s take a closer look at the
mechanism by which blood clotting occurs when a blood vessel is damaged, like the
one in this diagram, so that we can answer our question. We can see red blood cells and
platelets moving through a fluid called plasma in the blood vessel. And when damage occurs to the walls
of the blood vessels, these platelets start to clog up the damaged site and
aggregate to form a mass. Once platelets have been attracted
to the site of damage, they become activated and attract more platelets. Then, the platelets, together with
the surrounding tissue, release a molecule called thromboplastin, which the question
asks about.
In the presence of calcium ions,
thromboplastin acts on a protein produced by the liver called prothrombin,
converting it into the active enzyme thrombin. The enzyme thrombin acts on a
soluble protein found in blood plasma called fibrinogen, converting it into an
insoluble fiber called fibrin. Fibrin forms a net or mesh at the
site of damage, trapping more platelets and some red blood cells, which helps to
reinforce the mass forming a solid clot.
Now that we understand the process
of how blood clots form, let’s look back at the original question. What is the role of thromboplastin
in the process of blood clotting? The answer is (C): to initiate the
conversion of the protein prothrombin into the enzyme thrombin.
