Blood clotting

Vasoconstriction of damaged blood vessel Triggers Direct injury to vascular smooth muscle Chemicals released by endothelial cells and platelets Pain reflexes Most effective in smaller blood vessels

Positive Feedback cycle Damaged endothelium exposes collagen fibers Platelets stick to collagen fibers Swell, become spiked and sticky, and release chemical messengers

Reinforces platelet plug with fibrin threads Blood transformed from liquid to gel Series of reactions using clotting factors Vitamin K needed to synthesize 4 of them

Clot Retraction Stabilizes clot Actin and myosin in platelets CONTRACT within 30–60 minutes Contraction pulls on fibrin strands, squeezing serum from clot Draws ruptured blood vessel edges together

https://www.youtube.com/watch?v=P7KjyxN-_m4 https://www.youtube.com/watch?v=5tj4LTU9Nec https://www.youtube.com/watch?v=R-sKZWqsUpw&list=PL1A106F4D05105663