Lecture 22 Blood coagulation and wound healing Flashcards
Blood clotting (Coagulation) steps
- Injury/rupture to blood vessel
- Blood vessel around would constricts (reduces blood flow to injured area)
- Activated platelets stick to the injury site
- Platelets become sticky and clump together to form platelet plug
- Platelets and damaged tissue release clotting factors (factor VIII)
- Blood clotting mechanism to form fibrin which acts like a mesh to stop the bleeding
Hemostasis
the stopping of blood flow
2 types (primary and secondary)
Primary hemostasis
-Vasoconstriction and platelet response
What is platelet aggregation at the site of injury mediated by?
- Platlete derived agonists
- Platelet derived Adhesive proteins
- Plasma derived adhesive proteins
Secondary Hemostasis
- clotting cascade
- Cascade of coagulation serine proteases that culminates in the cleavage of soluble fibrinogen by thrombin (into fibrin)
Is fibrin soluble?
No, fibrin is insoluble and forms a clot.
When does fibrin generation occur?
Simultaneously to platelet aggregation
What cleaves fibrinogen to turn into insoluble fibrin?
thrombin
What do platelets release when they stick to collagen at the injury site?
- ADP
- Serotonin
- thromboxane A2
- (stored as dense granules)
What causes vasoconstriction?
Serotonin and Thromboxane A2
What attracts other platelets to stick together and form the platelet plug?
ADP
Thromboxane A2
Serotonin Biosynthesis
Tryptophan –> 5HTP –> Serotonin 5 hydroxytryptamine (5HT)
What is the first step in platelet aggregation?
Binding to VWF
- induces a conformational change on GPIIb/IIIa to bind to fibrinogen
Extrinsic pathway
The extrinsic pathway is activated by external trauma that causes blood to escape from the vascular system. This pathway is quicker than the intrinsic pathway. It involves factor VII
Intrinsic Pathway
Activated by the trauma inside the vascular system and is activated by platelets, exposed endothelium, chemicals , or collagen.
Slower than the extrinsic but more important
What activates the intrinsic pathway?
- platelets
- exposed endothelium
- collagen
- chemicals
What factors are involved in the intrinsic pathway?
- XII
- XI
- IX
- VIII
Common pathway
- Both pathways meet and finish the pathway of clot production in what is know as the common pathway.
What factors are involved in the common pathway?
- I
- II
- V
- X
What the coagulation factors generally?
Serinen proteases
What factors are glycoproteins?
- Factor V
- Factor VIII
Why is Ca important in the intrinsic and extrinsic pathways?
- Need calcium and phospholipids to activate factor X
- thrombin then turns fibrinogen into fibrin
Factor 1
Fibrinogen
-Cleaved by thrombin
Factor II
Prothrombin
ACtivated on surface of activated platelets by prothrombinase complex
What functions to hold enzymes onto the surface of the cell membrane?
Carboxyglutamate
Allow membrane interactions to continue pathways
What are the fat soluble vitamins?
- Vitamin D
- Vitamin E
- Vitamin A
- Vitamin K
What are the vitamin K dependent clotting factors?
- II
- VII
- IX
- X
When does fibrin start laying down a meshwork to reinforce the clot?
As soon as the platelet first attaches
- (highly organized cross link mesh of fibrin)
Why does the fibrin clot eventually need to go away?
In pulmonary vessels clot could break off and go to brain
Could cause stroke
What degrades fibrin polymer?
Plasmin
What activates plasminogen so it can break down fibrin?
Factors XIa, XIIa, Kallikrein
What are the stages of wound healing?
- Hemostasis
- Inflammation
- Proliferative
- Remodeling
Hemostasis
within minutes of post injury, platelets aggregate at the injury site to form a fibrin clot which acts to control bleeding (restricting blood flow)
Inflammatory phase
- Bacteria and debris are phagocytosed and removed from the wound site
- Factors are released that cause migration and division of cells involved in the proliferative phase
Proliferative phase
- Angiogenesis
- collagen deposition
- Granulation tissue formation
- Epithelization
- Wound contraction