HEMOSTATIS Flashcards
Hemostasis or blood clotting:
Why?:
Minimizes blood loss Maintains blood pressure Maintains tissue oxygenation Maintains electrolyte balance All intended to maintain & sustain life
What is hemostasis?
Hemostasis is a series of events that forms a blood clot to “plug” a broken or leaking blood vessel.
WHAT ARE THE 5 STAGES OF HEMOSTASIS?
A. Vascular Spasm. B. Platelet plug formation. C. Coagulation. D. Clot retraction. E. Thrombolysis.
A. Vascular Spasm Step
- A blood vessel is injured initially
- The injured vessel blood leaks into the extracellular space and fluid.
- Vasoconstriction and increased tissue tension occurs inside and on the surface of the vessel over the injury site.
Both will decrease blood vessel diameter.
A decrease in diameter will decrease local blood pressure & decreased blood flow will result in a decrease of blood loss at the injured site.
B. Platelet Plug Formation Step
The platelets act to plug and cork to stop the bleeding.
. The collagen fibers and chemicals in the outermost (tunica adventitia) layer of the torn vessels are exposed.
The injured endothelial cells (inner layer) release a glycoprotein called von Willebrand factor (vWF).
vWF binds to receptors on the plasma membrane of platelets to activate them.
b . The collagen fibers and chemicals in the outermost (tunica adventitia) layer of the torn vessels are exposed.
The injured endothelial cells (inner layer) release a glycoprotein called von Willebrand factor (vWF).
vWF binds to receptors on the plasma membrane of platelets to activate them.
C. Coagulation phase
Coagulation is the conversion of the soft platelet plug into a solid harder mass by fibrinogen.
Fibrinogen are protein fibers carried in the plasma that sticks & binds platelets, endothelial cells and all the other formed elements around the injured site.
Normally fibrinogen is initially in an inactive form in the blood prior to becoming activated from a bleed.
Fibrinogen will be stimulated to change into the active Fibrin by a series of reactions called the coagulation cascade.
These cascade reactions occur inside the torn vessel & on the surface of the platelets and/on the outer endothelial cells layer of the vessel.
Fibrinogen will be stimulated to change into the active Fibrin by a series of reactions called the coagulation cascade.
These cascade reactions occur inside the torn vessel & on the surface of the platelets and/on the outer endothelial cells layer of the vessel.
The Intrinsic Pathway
Intrinsic pathway: all factors are located in the blood.
Initiated when clotting factor XII ( Hageman factor) contacts exposed & loose collagen fibers from torn or disrupted vessels.
a. Exposed loose collagen fibers contact & activate factor XII.
The negative charges on expose collagen attract and bind clotting factor XII and activate it to become XIIa.
b. Factors IX & XI have now become activated.
Factors IX and & now factor VIII along with calcium ions form a new enzyme complex, This complex activates factor X ( Stuart factor)
Factor X activation ends the intrinsic pathway process.
Calcium ions are essential for the interaction of many factors with platelets in the platelet plug.
The Extrinsic Pathway
This Pathway occurs simultaneously along with the intrinsic pathway and involves factors outside of the blood vessel.
c. Factor VII, tissue factor III and calcium ions combine to form an enzyme complex that will also activates factor X (as we saw in the Intrinsic Pathway previously). Factor X formations end the extrinsic pathway.
Calcium ions here also are required for the interaction of these factors with platelets in the platelet plug
c. Factor VII, tissue factor III and calcium ions combine to form an enzyme complex that will also activates factor X (as we saw in the Intrinsic Pathway previously). Factor X formations end the extrinsic pathway.
Calcium ions here also are required for the interaction of these factors with platelets in the platelet plug
