Choose the correct order for the steps of hemostasis:
Select one:
- a. Blood coagulation, platelet plug formation, blood vessel spasm
- b. Blood vessel spasm, blood coagulation, platelet plug formation
- c. Blood vessel spasm, platelet plug formation, blood coagulation
- d. Platelet plug formation, blood coagulation, blood vessel spasm
The Correct Answer and Explanation is:
Correct Answer:
c. Blood vessel spasm, platelet plug formation, blood coagulation
Explanation
Hemostasis is the physiological process that stops bleeding at the site of an injured blood vessel. It is a critical mechanism that prevents excessive blood loss and maintains vascular integrity. Hemostasis occurs in three sequential and overlapping steps: vascular spasm, platelet plug formation, and blood coagulation.
- Blood Vessel Spasm (Vasoconstriction):
This is the immediate response to blood vessel injury. The damaged vessel constricts (vasospasm) to reduce blood flow and limit blood loss. This contraction is triggered by endothelial injury, local pain receptors, and the release of vasoconstrictors such as serotonin from platelets. Vasoconstriction is short-term but essential for slowing the bleeding and allowing the next steps to take place more effectively. - Platelet Plug Formation:
Platelets are attracted to the site of injury where they adhere to the exposed collagen of the damaged endothelium. This adhesion is facilitated by von Willebrand factor (vWF). Once attached, platelets become activated and release chemical mediators (ADP, thromboxane A2, serotonin), which recruit more platelets to the site. The aggregation of platelets forms a temporary “platelet plug”, which provides an initial barrier to further blood loss. - Blood Coagulation (Clotting Cascade):
This is a more stable and long-lasting response that reinforces the platelet plug with a fibrin mesh. The coagulation cascade involves a series of enzymatic reactions that lead to the conversion of fibrinogen (a soluble plasma protein) into fibrin (an insoluble protein). Fibrin strands weave through the platelet plug, solidifying it into a stable blood clot.
In summary, hemostasis begins with blood vessel spasm to reduce flow, followed by platelet plug formation to create a temporary barrier, and concludes with blood coagulation to form a stable clot. These steps are tightly regulated to prevent both excessive bleeding and unwanted clotting.
