Ch 11.4B -- Platelets and Hemostasis -- VTPP 435

Ch 11.4B -- Platelets and Hemostasis -- VTPP 435

Intrinsic Pathway

-pathway started by factor XII (Hageman factor)
-started when factor comes in contact with exposed collagen in an injured vessel or a foreign surface
-uses 7 steps

Extrinsic Pathway

-uses 4 steps
-requires contact with tissue factors external to blood to start clotting of blood
-Tissue Thromboplastin is released when tissue is traumatized

Clot Retraction

-formed once clot is formed
-occurs as trapped platelets contract and shrink the fibrin mesh and pull the edges of vessel closer
-fluid squeezed from clot

Serum

-plasma minus fibrinogen and other clotting precusors
-squeezed out of a clot

Vessel Repair

-aggregated platelets secrete a chemical to allow fibroblasts to invade a wounded area and form a scar

Plasmin

-fibrinolytic enzyme dissolve the clot when it is not needed
-made by liver as inactive in the form of plasminogen
-activated by Hageman factor

Tissue Plasminogen Activator (tPA)

-activates plasmin
-released from tissues especially the lungs

Thrombus

an abnormal intravascular clot attached to a vessel wall

Emboli (singular Embolus)

freely floating clots

Different Factors can cause Thromboembolism

1) Roughened vessel surfaces with atherosclerosis
2) Imbalances in clotting
3) slow moving blood is more apt to clot
4) widespread clotting triggered by release of tissue thromboplastin into blood from large amounts of traumatized tissue

Septicemic Shock

-when bacteria or their toxins initiate clotting cascade
-a form of widespread clotting

Hemostatic Disorder

-failure of clots to form properly in injured vessels
-results in hemorrhage or mild traumas

Hemophilia

-most common cause of excessive bleeding
-results from deficiency in one of the factors of the clotting cascades

Thrombocytopenia Purpura

-a platelet deficient person with diffuse capillary hemorrhage in skin as small purplish blotches