1. MLAB 1227- Coagulation Keri Brophy-Martinez
Overview of Hemostasis:
Part One

2. Hemostasis Heme= blood stasis= to halt
Process of retaining blood within the vascular system
Repairs injury to blood vessels
Stops or prevents blood loss

3. Balance of Hemostasis Procoagulant Factors Regulatory Factors Fibrin
Fibrinogen
Procoagulant Factors
Regulatory Factors
Fibrin
Balance of Hemostasis
*Balance of bleeding (hemorrhaging) and clotting (thrombosis)
*Imbalance in one direction can lead to:
bleeding : hypocoagulable state OR
thrombosis: hypercoagulable state

4. Hemostasis Components Vascular System Platelet System
Controls rate of blood flow
Platelet System
Interaction of vasculature and platelets form a temporary plug
Coagulation System
Forms a stable insoluble plug (i.e) fibrin forming
Fibrinolytic System
Fibrin lysing
Coagulation Inhibition System
Natural inhibitors
Control fibrin formation and fibrin lysis

5. Hemostasis
Failure or deficiencies in any of the five systems involved with hemostasis can leads to varying degrees of uncontrolled hemorrhaging or clotting

6. Hemostasis
The hemostatic components remain inert in the presence of intact vascular tissue or endothelium
Following injury, each component must function optimally.

7. Hemostasis: Overview Consists of three stages
Primary Hemostasis
Process of blood clotting in response to injury or desquamation of dying /damaged endothelial cells
Blood vessels (vasculature) and platelets are the main “players.”
Primary Hemostatic plug is formed
Platelet plug temporarily arrests bleeding. Insoluble fibrin strands deposit on the initial plug to reinforce and stabilize. The fibrin originates from soluble plasma proteins.
Secondary Hemostasis
Actions of the protein coagulation factors form fibrin in response to injury
Fibrin is stabilized by Factor XIII
At this time, blood has changed into a solid state
Fibrinolysis
Clot is removed following healing of wound

8. Stages of Hemostasis

9. Vascular System Components Arteries/ Arterioles
Carry blood from the heart to capillaries
Thickest walls of the vasculature
Veins/Venules
Return blood from capillaries to the heart
Thinnest walls of vasculature
Capillaries
No vessel wall
Do not contribute to hemostasis

10. Vascular System: Anatomy of the Blood Vessels
Structure
Endothelium
Single layer of endothelial cells, lining vessels
Coated by glycocalyx (protein and mucopolysaccarides)
Protects basement membrane
Negatively charged, repels circulating proteins and platelets
Secretes substances to keep the blood vessel in a nonreactive environment

12. Vascular System: Anatomy of the Blood Vessels
Structure con’t
Subendothelium
Smooth muscle and connective tissue with collagen fibers
Basement membrane
Collagen– stimulates platelets
Tissue Factor (TF)- activates coagulation & fibrin formation
Connective tissue
Elastic fibers- provide support around vessels

13. Vascular System: Blood Vessels
Daily Function
Endothelium
Controls vessel permeability
Controls blood flow rate
Produces and releases substances that inhibit OR stimulate platelets, coagulation and fibrinolysis

14. Hemostatic Trigger Once vessel damage occurs, action begins!
Arteries and arterioles vasoconstrict
Smooth muscle cells contract to reduce blood flow
The endothelium becomes thrombogenic
Platelets and coagulation proteins are activated
VWF is secreted
Fibrinolysis initiated

15. How Does the Endothelium Become Thrombogenic?
Actions
Von Willebrand’s Factor is made and released to assist the platelets in primary hemostasis
Produce tissue factor needed for secondary hemostasis
Collagen is exposed which secretes platelet activating factor which in turn activates platelets
Subendothelium promote the binding of leukocytes
Plaminogen activator inhibitor is released to inhibit fibrinolysis

16. Resting “Normal”

17. Vascular System: Function Following Injury
Initiate hemostasis: FIRST RESPONSE
Vasoconstriction of the arterioles
Minimizes blood flow to injured area
Prevents blood loss
Delivers platelets and plasma proteins to the vessel wall
Immediate
Short-lived

18. Vasoconstriction Mechanism Neurogenic factors Regulatory substances
Prolong vasoconstriction
Serotonin ( product of platelet activation & endothelium)
Thromboxane A2 ( product of platelet activation & endothelium)
Endothelin-1 (product of damaged endothelial cells)

19. Roles of the Healthy Endothelium
Prostaglandin (PGI2)/ Prostacyclin and Nitric Oxide
Vasodilates to increase blood flow to bring fresh supplies of clotting substances
Inhibits platelet aggregation & recruitment
Causes redness at the injury site

20. Additional Roles Contraction of venules Inflammatory response
Causes gaps between them which pushes fluids causing edema or swelling
Inflammatory response

21. References
McKenzie, Shirlyn B., and J. Lynne. Williams. "Chapter 29." Clinical Laboratory Hematology. Boston: Pearson, 2010.
eMedTV. (2009, August 12). How Does Blood Clot.[Video file]. Retrieved from