Overview
This lecture introduces hemostasis, the process the body uses to stop bleeding, and explains its three main steps: vascular spasm, platelet plug formation, and coagulation, along with the roles of blood vessel anatomy and clotting factors.
Hemostasis Overview
- Hemostasis is the process that stops bleeding after blood vessel injury.
- It involves three main steps: vascular spasm, platelet plug formation, and coagulation.
Vascular Spasm
- Vascular spasm is the immediate constriction of a damaged blood vessel to reduce blood loss.
- Blood vessels have three layers: outer collagen-rich connective tissue, middle smooth muscle, and inner slick endothelium.
- Injury to smooth muscle, chemicals from damaged endothelium and platelets, and pain receptor activation all trigger vascular spasm.
Platelet Plug Formation
- Platelets (thrombocytes) stick to exposed collagen at the injury site, forming a soft plug.
- Healthy, intact endothelium prevents unwanted platelet adhesion.
- Platelet plug formation uses positive feedback, where platelets attract more platelets to build the plug.
Coagulation and Clotting Cascade
- Coagulation turns blood from a liquid to a solid by creating a net-like protein structure that traps blood cells.
- The process involves a cascade of chemical reactions, activating clotting factors (pro-coagulants) in sequence.
- There are 12 clotting factors, named with Roman numerals I–XIII (with no Factor VI), normally inactive until vessel injury.
- The cascade starts with Factor XII, leading to sequential activation down to Factor I (fibrinogen) and Factor XIII, which cross-links fibrin strands to form the net.
Hemophilia and Snake Venoms
- Hemophilia is a condition where a person lacks certain clotting factors, commonly Factor VIII or IX, interrupting the cascade and preventing clot formation.
- Some snake venoms activate certain clotting factors, causing rapid clotting, while others inhibit factors and prevent clotting.
Key Terms & Definitions
- Hemostasis — the body's process to stop bleeding.
- Vascular spasm — constriction of a blood vessel after injury.
- Platelet plug — a temporary aggregation of platelets at a vessel injury site.
- Coagulation — transformation of blood from liquid to solid by forming a protein net.
- Clotting factors (pro-coagulants) — blood proteins that mediate coagulation, numbered I-XIII.
- Endothelium — the thin, slick inner lining of blood vessels.
- Hemophilia — a genetic disorder with missing clotting factors, leading to poor clotting.
Action Items / Next Steps
- Complete the activity on hemophilia and snake venom effects on coagulation.
- Consider watching YouTube videos demonstrating snake venom’s effect on blood.