Download Overview of Hemostasis

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

Procoagulant
Factors
F
i
b
r
i
n
o
g
e
n
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
Hemostasis

Components

Vascular System


Platelet System


Forms a stable insoluble plug (i.e) fibrin forming
Fibrinolytic System


Interaction of vasculature and platelets form a temporary plug
Coagulation System


Controls rate of blood flow
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: 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
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 vasoconstrict
 Smooth muscle cells contract to reduce blood
flow
 The 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

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)

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 venules
 Causes
gaps between them which pushes
fluids causing edema or swelling

Inflammatory response
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
http://www.youtube.com/watch?v=-bZUeb83uU
