Introduction to Hemostasis PDF

MLS 323 Introduction 1 to hemostasis 2 Define hemostasis and identify the essential components of the process. Describe and compare the histological features of the tissues of the arteries and veins. Objectives...

MLS 323 Introduction 1 to hemostasis 2 Define hemostasis and identify the essential components of the process. Describe and compare the histological features of the tissues of the arteries and veins. Objectives Name the blood vessels that constitute the microcirculation and compare their size and other features with those of arteries and veins. Define the term vasoconstriction and Explain how it participates in hemostasis.  Hemostasis can be defined as: the stoppage of bleeding from the blood vessels Introduction to It is a complex process in which several factors work 3 together or in sequence to stop the flow of blood hemostasis from an injured blood vessel. The five major components of normal hemostasis are platelets, coagulation factors, coagulation inhibitors, fibrinolysis and blood vessels.  4  Under normal conditions, the formation and dissolution of thrombi is maintained in a delicate balance  Without this balance, the individual may experience either excessive bleeding or Vaso-occlusion (thrombosis)  5 Hemostasis can be divided into two stages: 1- Primary 2- Secondary. - Primary hemostasis includes the platelet and vascular response to vessel injury. - Secondary hemostasis includes the coagulation factors response to such injury.  Blood vasculature 6  7 Vasculature Physiology The Role of Vasoconstriction in Hemostasis  Vascular injury to a large or medium – size artery or vein requires rapid surgical intervention to prevent depriving the body from blood.  When a small vessel, such as an arteriole, venule, or capillary injured, contraction of the blood vessel wall is called vasoconstriction.  Vasoconstriction is a short-lived reflex reaction of the smooth muscle in the vessel wall produced by the sympathetic branches of the autonomic nervous system.  The role of the Endothelium 8 The endothelium is involved In :-  The metabolism and clearance of molecules such as serotonin , angiotensin, and bradykinin that affect blood pressure regulation.  The movement of fluid across the endothelium, and inflammation.  With respect to blood coagulation, one of the basic characteristics of normal intact endothelium is its non- reactivity with platelets and inability to initiate surface activation of clotting factor XII.  Function of Endothelium 9  The connective tissue matrix of the endothelium (i.e. collagen and elastin) regulates the permeability of the inner vessel wall and provides the principal stimulus to thrombosis following injury to blood vessel.  It is involved in clotting process by producing or sorting clotting components. 10  Disruption of the endothelium directly activates the components 11 of hemostasis. After this event, the following vents take place:  Initially rapid vasoconstriction for up to half an hour reduces blood flow and promotes contact activation of platelets and coagulation factors.  In the second phase, platelets adhere immediately to the exposed subendothelial connective tissue, particularly collagen.  The aggregated platelets enhance sustained vasoconstriction by releasing thromboxane A2 and vasoactive amines, including serotonin and epinephrine.  In the third phase, coagulation is initiated through both the intrinsic and extrinsic systems  12 Maintenance of vascular Integrity  Vascular integrity to vessel disruption requires three essential factors. 1) Circulating functional platelets, 2) Adrenocorticosteroids 3) Ascorbic acid.  The integrity of arterioles and venules depends on vasoconstriction, the formation of a plug of fused platelets over the injury, and the formation of a fibrin clot.  Arteries are the most resistant to bleeding; however, hemorrhage from these vessels is the most dangerous 13 References  Clinical Hematology :- Theory and Procedures, 6th Edition, by Mary Louise Turgeon  Essential Haematology: By: Hoffbrand, A. V. Malden, Mass.: Blackwell Pub., 2011.  Dacie and Lewis practical haematology 10th ed., Indian ed. Author Lewis, S. M. (Shirley Mitchell).