Platelet and Primary Hemostasis PDF

27/11/1443 By Abdulfatah albakkoush Introduction: • The platelets are the smallest of the circulating hematological elements. • The platelets are derived from precoursor cells in the bone marrow called Megakaryocyte. • They are not truly cells but are membrane-bound anucleate fragments of cytoplas...

27/11/1443 By Abdulfatah albakkoush Introduction: • The platelets are the smallest of the circulating hematological elements. • The platelets are derived from precoursor cells in the bone marrow called Megakaryocyte. • They are not truly cells but are membrane-bound anucleate fragments of cytoplasm of megakaryocyte. • platelet circulate at a concentration of 150 - 450 X 𝟏𝟎𝟗 \L. • platelet under microscope appear as small, lavander-blue or colorless bodies with reddish-purple granules. 1 27/11/1443 Introduction: • several cytokines and growth factors affect megakaryocyte development like IL-3,IL6,IL 11 and GM-CSF. • the major humeral factor regulating megakaryocyte and platelet development is thrombopiotein. • circulating platelet repel one another and the surface of endothelial cells of blood vessel. • After an injury, many changes affecting platelet morphology and biochemistry causing the platelet to become activated after interact with blood vessel and other platelet to form primary hemostatic plug. 2 27/11/1443 Structure of the platelet: The platelet ultra-stucture divided into four zone: 1-peripheral zone 2-structural zone 3-organelle zone 4-membrane system 1-peripheral zone: • The platelet peripheral zone consists of a phospholipid membrane covered on exterior by surface coat and on the interior by a thin membrane. • its responsible for the platelet surface negative charge that prevent platelets from interacting with each other and with negatively charged endothelia cells. • the cytoplasmic membrane contains membrane receptors involved in platelet function. 3 27/11/1443 2-structural zone: • Its consists of microtubules, microfilaments and intermediate filaments. • Its function stabilize the platelet resting discoid shape, and provide shape change when the platelet is activated. 3- Organelle zone: • its consists of mitochondria, glycogen particles and four types of granules: dense granules,α granules,lysosomes and peroxisomes. • Its function in platelet activation. 4 27/11/1443 4- Membrane System: -the platelet membrane system consists of : 1-The open canalicular system: its invagination of the plasma membrane. - Its provide the both the entry of the external substances into the interior of the platelet and release of the granules contents to the outside, 2-The dense tubular system: -its storage site for ionized calcium and release of calcium when the. platelet is activated - FUNCTION OF THE PLATELET 1- maintain of blood vessel integrity. 2- platelet-platelet interaction( primary hemostatic plug) 3- platelet-coagulation protein interaction( secondary hemosatic plug) 4-Aid in healing injured tissue. 5 27/11/1443 Platelet and primary hemostasis: Hemostasis: is the property of the circulation that mantaions blood as fluid within the blood vessels under normal condition and the system ability to prevent excessive blood loss upon injury. - Maintaining blood fluidity requires the presence of healthy vascular endothelium, inactive platelet and plasma coagulation proteins. - In contrast, the control of bleeding requires the activation of platelet and plasma coagualtion proteins rapidly. Platelet and primary hemostasis: • Hemostasis is the result of the interaction between the blood vessel (through vasoconstriction, decreased blood flow to the wounded region, and prevention of blood loss), platelets, and coagulation proteins. • Primary hemostasis, secondary hemostasis, and fibrinolysis are the three phases of hemastasis. 6 27/11/1443 Primary Hemostasis -During primary hemostasis the platelet interact with injured vessels and with one another. - This intraction produces a mass of platelets referred to as the primary hemostatic plug, which is unstable and quickly removed from the circulation. - platelet plug: is the barrier mass formed to limit blood loss. formation of primary hemosatic plug: • when vessel injury occurs, the platelets react by forming the primary hemostatic plug. • During primary hemostasis platelet the platelet interact with injured vessels and with each other that result in formation of primary hemostatic plug. • The formation of platelet plug require several activation event including: adhesion, shape change, secretion and aggregation. 7 27/11/1443 1- Platelet Adhesion: • Platelets' primary purpose is to repair damaged blood vessels. • Exposure of sub-endothelium components of the vessel wall, which are normally hidden from circulating platelets, is the first stimulation for platelet activation. • The sub-endothelium includes several adhesion proteins with which platelets may bind through particular membrane receptors. 8 27/11/1443 2- Platelet activation: • Platelet adhesion to sub-endothelium triggers a series of morphological and functional changes known as platelet activation. • Activation includes changes in metabolic biochemistry, platelet morphology, surface receptor and membrane phospholipid. • An agonist is a substance that induces platelet activation. Some agonists are created by platelets and others by other cells near the damage site. 9 27/11/1443 10 27/11/1443 3- Platelets shape change: • Platelets activated by agonists change from disc-shaped to spiny spheres with pseudopods. • Microtubules, actin, and myosin filaments rearrange during shape change. • Platelet granule release facilitates platelet granule release into surrounding tissues, activating platelets. 4- Platelets aggregation: • The aggregation of Platelets is the joining of Platelets together. • During Platelets adhesion, collagen-binding induces intracellular signalling that activates a specific receptor on the platelets surface, which binds soluble fibrinogen. • fibrinogen may connect two platelets. 11 27/11/1443 12