Life sciences explore the causes behind physiological phenomena. Professor Xianchi Dong’s lecture on this subject took us into the microscopic world of blood to investigate complicated processes behind those physiological phenomena that we had taken for granted before.

Injuries may cause bleeding and after some time, the bleeding will stop, which is called coagulation, or blood clotting. Throughout history, the exploration of coagulation began in the 3rd or 4th century BC. Modern theories of blood coagulation have been established for more than 100 years, from the basic conjectures in the 1900s to the discovery of various coagulation factors and related chemical reactions later. However, studies on the blood system are still far from enough. In China, nearly 50% of deaths were caused by hematologic diseases, such as stroke, myocardial infarction, deep vein thrombosis, disseminated intravascular coagulation, hemophilia, etc. Therefore, with further studies in coagulation, we will probably be able to treat hematologic diseases as well as improve people’s life quality

Then Professor Dong gave us more insights into the chemical reactions related to coagulation. First was a general picture of a circulatory system: it consists of a closed system of vessels and the heart, with blood flowing through it. The main components of blood are red blood cells, white blood cells, and platelets. Platelets play a major role in blood clotting, which mainly includes four steps: vasoconstriction, platelet activation and coagulation cascade (primary and secondary coagulation), clot retraction, and thrombolysis.

Step 1: The damage of endothelial cells causes the release of certain factors, which alter blood flow velocity and vascular morphology.

Step 2: The processes of primary and secondary coagulation are well studied. Platelet receptors specifically recognize substances released by injured endothelial cells, such as von Willebrand factors (vWF) and collagen, which triggers platelets to deform and release signaling molecules (e.g. ADP) and thus recruit other platelets to adhere to the injury site. The coagulation factor X is then activated via the intrinsic (starting with factor III) and extrinsic (starting with factor XII) pathways, which results in a positive-feedback coagulation cascade and formation of blood clots through the pathway: prothrombin → factor II (thrombin)→factor I (fibrinogen).

Step 3: The clot retraction pulls the injury site closer. However, studies on this process are still inadequate.

Step 4: Substances such as TPA and UPA dissolve fibrin and prevent the clots from growing bigger.

In Professor Dong’s lecture, we learned about a series of complicated but ingenious chemical reactions behind a simple physiological phenomenon, and the prospects of this field in the future. It is worth noticing that one of the induced diseases by COVID-19 is disseminated intravascular coagulation, which also demonstrates our need for updated coagulation knowledge to face future challenges.