Hemostasis

Lore & Background

Hemostasis occurs when blood is present outside of the body or blood vessels. It is the innate response for the body to stop bleeding and loss of blood. During hemostasis three steps occur in a rapid sequence.

Vascular spasm is the first response as the blood vessels constrict to allow less blood to be lost. In the second step, platelet plug formation, platelets stick together to form a temporary seal to cover the break in the vessel wall. The third and last step is called coagulation or blood clotting, which reinforces the platelet plug with fibrin threads that act as a 'molecular glue.'

Reader's Guide

Hemostasis is essential for survival, as it prevents excessive blood loss from injuries. Its significance extends beyond natural processes: in emergency medicine and surgery, various methods—such as chemical/topical agents, direct pressure, and sutures—are used to achieve hemostasis when the body cannot do so naturally.

The process is also central to understanding disorders like hemorrhage (the opposite of hemostasis) and thrombosis, where clots form inappropriately. Debates among physicians and medical practitioners continue on how to handle situations with large injuries, but it is universally accepted that hemostatic agents are the primary tool for smaller bleeding injuries. Developmental haemostasis refers to differences in the haemostatic system between children and adults, highlighting that the process varies across life stages.

Did You Know?

• Platelets release cytoplasmic granules containing serotonin, ADP, and thromboxane A2, which increase vasoconstriction.
• The word 'hemostasis' comes from Ancient Greek roots meaning 'blood' and 'stasis' (stopping).
• Intact endothelial cells prevent blood clotting with a heparin-like molecule and thrombomodulin, and prevent platelet aggregation with nitric oxide and prostacyclin.