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

MLAB 1227- Coagulation

Keri Brophy-Martinez

Overview of Hemostasis:Part One

Hemostasis

Heme= blood stasis= to halt Process of retaining blood within the

vascular system Repairs injury to blood vessels Stops or prevents blood loss

Balance of Hemostasis

*Balance of bleeding (hemorrhaging) and clotting (thrombosis)

*Imbalance in one direction can lead to:

bleeding : hypocoagulable state OR

thrombosis: hypercoagulable state

Procoagulant Factors

Regulatory Factors

Fibrin

Hemostasis Components

Vascular 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

Hemostasis

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

Hemostasis

The hemostatic components remain inert in the presence of intact vascular tissue or endothelium

Following injury, each component must function optimally.

Hemostasis: OverviewConsists 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

Stages of Hemostasis

http://tinyurl.com/8w8redf

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

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

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

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

Hemostatic Trigger

Once vessel damage occurs, action begins!Arteries and arterioles vasoconstrictSmooth muscle cells contract to reduce blood

flowThe endothelium becomes thrombogenic

Platelets and coagulation proteins are activated VWF is secreted Fibrinolysis initiated

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

Resting “Normal”

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

Vasoconstriction

MechanismNeurogenic factorsRegulatory substances

Prolong vasoconstriction Serotonin ( product of platelet activation &

endothelium) Thromboxane A2 ( product of platelet activation &

endothelium) Endothelin-1 (product of damaged endothelial

cells)

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

Additional Roles

Contraction of venulesCauses gaps between them which

pushes fluids causing edema or swelling

Inflammatory response

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 http://www.youtube.com/watch?v=--bZUeb83uU

References