Overview
This lecture explains how blood vessels repair damage through the formation of a platelet plug and a fibrin-based clot, and introduces key blood clotting proteins and mechanisms.
Structure of Blood Vessels
- Blood vessels are tubes that transport blood throughout the body.
- The vessel walls are made of tightly connected endothelial cells to prevent blood leakage.
- Each endothelial cell has a nucleus.
Platelet Plug Formation
- When a blood vessel is damaged and endothelial cells break open, blood can leak out.
- Platelets, which are cell fragments without a nucleus, circulate in the blood and plug vessel holes.
- Platelets clump only at damage sites, not randomly, due to environmental triggers.
- Collagen, a structural protein found outside blood vessels, interacts chemically with platelets at wound sites, triggering aggregation and forming a platelet plug.
Fibrin Clot Formation
- The platelet plug is the first step in stopping blood loss but is not strong enough alone.
- Fibrin, a protein, reinforces the platelet plug by forming a mesh that holds platelets together.
- Fibrin is formed from fibrinogen, an inactive circulating protein that doesn't stick together due to an extra piece.
- Fibrinogen is converted to fibrin only at wound sites, preventing unwanted clots in circulation.
Activation of Clotting Proteins
- Tissue factor, a protein found outside blood vessels, activates clotting only at injury sites.
- Tissue factor initiates a series of activations, called the coagulation cascade, leading to massive production of thrombin.
- Thrombin is the enzyme that converts fibrinogen into fibrin, forming the stable meshwork.
- This cascade efficiently amplifies the production of fibrin where needed.
Key Terms & Definitions
- Endothelial cell — cell lining the inner wall of blood vessels.
- Platelet — small, nucleus-free blood cell fragment that helps plug vessel injuries.
- Collagen — structural protein outside vessels that interacts with platelets.
- Platelet plug — initial blockage formed by platelets at a wound.
- Fibrin — protein mesh that stabilizes blood clots.
- Fibrinogen — inactive protein in blood, converted into fibrin during clotting.
- Tissue factor — protein outside vessels that triggers coagulation at injury sites.
- Thrombin — enzyme that converts fibrinogen to fibrin.
- Coagulation cascade — sequence of protein activations leading to blood clotting.
Action Items / Next Steps
- Review the process and key proteins involved in blood clotting.
- Optional: Research more details about the coagulation cascade.