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A&P Chapter 11-7

Hemostasis involves vascular spasm, platelet plug formation, and blood coagulation

Emily Sandy

on 9 February 2011

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Transcript of A&P Chapter 11-7

Chapter 11-7 Hemostasis and Clotting Hemostasis= process that halts bleeding, prevents the loss of blood through walls of damaged vessels. Steps in Hemostasis 1. The Vascular Phase

Walls of blood contain endothelium
Cutting the wall of a blood vessel triggers a contraction in the endothelium that decrease the vessel's diameter
This contraction is called a vascular contraction and can last up to 30 minutes 2. The platelet phase
Platelets attach to endothelial surfaces and exposed collagen fibers within 15 seconds of the injury
As more platelets arrive, they stick to one another
This forms a platelet plug that may close the break in the vessel wall 3. The Coagulation Phase
Does not start until 30 seconds or more after the vessel has been damaged
Involves a complex sequence of steps leading to the conversion of fibrinogen to fibrin
As this network of fibrin grows, blood cells and more platelets get trapped within the tangle and a blood clot forms The Clotting Process
Clotting Factors= Calcium ions and 11 different plasma proteins

Most of these plasma proteins are made by the liver

During the Coagulation phase, these proteins interact so that one is activated, which activates the second, and so on. This creates a chain reaction or cascade. This cascade involves 3 different pathways:
1. Extrinsic Pathway
2. Intrinsic Pathway
3. Common Pathway

Together, these pathways result in a blood clot
1. Extrinsic Pathway

-Shorter and faster pathway that initiates the clotting
-Begins with the release of a lipoprotein called tissue factor
-Tissue factor combines with Calcium Ions and Clotting Factor VII to activate 'Factor X' 2. Intrinsic Pathway
-Begins with activation of proenzymes
-These combine with a 'Platelet factor', Calcium ions, and other clotting factors to activate 'Factor X'
3. Common Pathway
-Begins with 'Factor X' from either/both intrinsic or extrinsic pathways
-'Factor X' then forms prothrobin, a clotting protein
-Prothrombin is this converted to thrombin, which completes the clotting process by converting fibrinogen to fibrin Vitamin K and Calcium ions are vital to all pathways

-Disorders that lower Ca in plasma directly affect the clotting process
-Vitamin K deficiency leads to break down of common pathway Look Figure 11-10 on pg 399 in book! Clot Retraction and Removal Once the fibrin forms, platelets and RBCs stick to the fibrin strands

Then the platelets contract and pull the torn edges of the wound closer together

Clot reaction= process that reduces the size of the damaged area, making it easier for the fibroblasts, smooth muscle cells, and endothelial cells in the area to make necessary repairs As repairs proceed, the clot dissolves
This is call fibrinolysis

Fibrinolysis begins with the activation of a plasma protein called plasminogen and tissue plasminogen activator (t-PA)

This activation of plasminogen makes plasmin, an enzyme that begins digesting fibrin strands and breaking down the clot
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