Hemostasis Flashcards
What is hemostasis?
Hemostasis is the mechanism that stops bleeding from a blood vessel.
How does endothelium prevent platelets from binding to the endothelial lining?
It produces Nitric oxide and PGI2 which inhibit the platelets and keep them inactive
Explain the vascular spasm mechanism, along with the myogenic mechanism as well as how inflammatory chemicals affect it.
When the endothelium is injured, it secretes endothelin which stimulates the smooth muscle to contract.
The myogenic method is when there is direct injury to the smooth muscle, which causes it to contract.
Finally, inflammatory chemicals can bind to nociceptors, activating them and causing them to stimulate the smooth muscles to contract
Explain platelet aggregation.
When injured, the endothelial cells no longer produce nitric oxide and prostacyclin. This allows platelets to bind to Von Wildebrons factor on their glycoprotein 1B receptors.
Platelets secrete ADP, TxA2, and serotonin. ADP and TxA2 stimulate other platelets, bringing them to the site of injury. The platelets then bind to one another VIA fibrinogen linking them by their glycoprotein IIB-IIIA receptors.
Explain the coagulation cascade.
Clotting factor 12 that flows in the blood is stimulated by the negative charge produced by the platelets and becomes active. Once active it activates factor 11 which activates factor 9. Platelet factor 3 and calcium stimulate factor 9 to form a complex with factor 8. This complex then activates factor 10
Activate factor 10 interacts with factor 5 to form a complex aided by platelet factor 3 and calcium. This leads to the activation of the Prothrombin activator.
Prothrombin activator converts prothrombin to thrombin(its active form)
Thrombin stimulates fibrinogen to polymerize becoming Fibrin
It also stimulates facto 13, which induces the cross-linking of fibrin polymers to form a fibrin mesh, that covers the platelet clot preventing it from dislodging
Explain clot retraction and repair.
This is when the platelets actin and myosin proteins stimulate contraction of the smooth muscle to bring the damaged edges of the endothelium closer together.
They also secrete “platelet-derived growth factor” which stimulates the proliferation of smooth muscle.
They also produce “vascular endothelial growth factor” which regenerates the endothelium
Explain fibrinolysis
The membranes of blood vessels contain “tissue plasminogen activator” which activates plasminogen converting it into plasmin. Plasmin degrades the fibrin mesh disintegrating the clot
