Chapter 17.3 - Forming clot Flashcards
What are platelets made off?
Small fragments of megakaryocytes
What is thrombopoietin?
The formation of platelets
How does a platelet look like?
Blue-staining outer region with purple granules
What do the granules contain in platelets?
Serotonin, Ca2+, enzymes, ADP and PDGF
What is hemostasis?
Fast series of reactions for stoppage of bleeding
Which three steps are involved with hemostasis
Vascular spasm, platelet plug formation, coagulation (blood clotting)
What is the tunica intima?
The innermost layer of the blood vessel wall made of simple squamous epithelium
What is the tunica media?
Middle layer of the blood vessel wall composed of smooth muscle and sheets of elastin
Where are the vasomotor nerve fibers in the tunica media for?
Vasoconstriction and vasodilation
What is the tunica externa (adventitia)?
The outermost layer of the blood vessel wall composed of loose collagen fibers
What is the vasa vasorum?
System of tiny blood vessels found in larger vessels
What is vascular spasm?
Vessel responds to injury with vasoconstriction
What triggers vascular spasm?
- Direct injury to vascular smooth muscle
- Chemicals released by endothelial cells and platelets
- Reflexes initiatied by local pain receptors
What is platelet plug formation?
Platelets stick to collagen fibers that are exposed when vessels are damaged
What prevents platelet sticking?
No collagen and prostacyclins
What does the von Willebrand factor
Helps to stabilize platelet-collagen adhesion
What is the function of the released chemical messenger of ADP in an activated platelet?
More platelets to stick and release their contents
Which chemical messengers of activated platelets enhance vascular spasm and platelet aggregation?
Serotonin and thromboxane A2
What do they call the following concept: as more platelets stick,
they release more chemicals, which cause more
platelets to stick and release more chemicals
Postive feedback cycle
What are platelet plugs fine for?
Small vessel tears
What does coagulation do?
Reinforces platelet plug with fibrin threads
How are clotting factors activated?
They are turned into enzymes by clipping off a piece of the protein, changing shape
What are the three phases of coagulation?
- Prothrombin activator is formed
- prothrombin is converted into thrombin
- Thrombin catalyzes te joining of fibrinogen to form a fibrin mesh
How ends the intrinsic or extrinsic pathway?
The activation of factor X which then complexes with Ca2+, platelets and factor V to form prothrombin activator
How is the intrinsic pathway triggered?
By negatively charged surfaces such as activated platelets, collagen, or even glass of a test tube
How is the extrinsic pathway triggered
By exposure to tissue factor (TF); factor III
What is the name for clotting factors?
Procoagulants
What are important plasma proteins in coagulation?
I to XIII and vitamin K
Describe the pathway to thrombin (phase 2)
The prothrombin activator catalyzes transformation of prothrombin to activate enzyme thrombin
What are anticoagulants?
Factors that normally dominate in blood to inhibit coagulation
How is fibrinogen coverted to fibrin?
With thrombin
Why activates thrombin factor XIII?
To form cross-link fibrin and to strengthen and stabilizes the clot
