ASCP Specialist in Blood Banking (SBB) Practice Exam

Platelets are the cells responsible for clotting in blood. They are small, disc-shaped cell fragments derived from the cytoplasm of megakaryocytes in the bone marrow. When blood vessels are injured, platelets swiftly adhere to the site of damage and aggregate to form a temporary 'platelet plug.' They also release various substances, including clotting factors, which stimulate further clot formation and help to stabilize the initial plug.

In addition to binding together and interacting with each other, platelets activate the coagulation cascade, a complex series of events that culminates in the conversion of fibrinogen to fibrin, leading to a more stable blood clot. This process is critical in stopping hemorrhage and initiating the healing of injured tissues.

The other cell types mentioned have different roles; red blood cells primarily transport oxygen and carbon dioxide, white blood cells are involved in immune responses, and stem cells serve as precursors to various blood cell lineages, but none are directly involved in the clotting process.