Platelet and Primary Hemostasis Lecture 6 PDF

13 February 2023 LECTURE 6 PLATELET AND PRIMARY HEMOSTASIS by Abdulfatah Albakkosh Introduction: • The platelets are the smallest of the circulating hematological elements. • The platelets are derived from precoursor cells in the bone marrow called Megakaryocyte. 13 February 2023 LECTURE 6 In...

13 February 2023 LECTURE 6 PLATELET AND PRIMARY HEMOSTASIS by Abdulfatah Albakkosh Introduction: • The platelets are the smallest of the circulating hematological elements. • The platelets are derived from precoursor cells in the bone marrow called Megakaryocyte. 13 February 2023 LECTURE 6 Introduction: • They are not truly cells but are membrane-bound anucleate fragments of the cytoplasm of megakaryocytes. • platelet circulates at a concentration of 150 − 450 × 10 \L . • platelet under the microscope appears as small, lavender-blue, or colorless bodies with reddish-purple granules. 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 thrombopoietin. • circulating platelet repel one another and the surface of endothelial cells of blood vessels. 13 February 2023 LECTURE 6 Introduction: • After an injury, many changes affecting platelet morphology and biochemistry cause the platelet to become activated after interacting with blood vessels and other platelets to form a primary hemostatic plug. Introduction: 13 February 2023 LECTURE 6 Structure of the platelet: The Platelet Ultra-structure Divided Into Four Zones: 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. 13 February 2023 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: • It consists of mitochondria, glycogen particles, and four types of granules: dense granules,α granules, lysosomes, and peroxisomes. • Its function in platelet activation. LECTURE 6 13 February 2023 LECTURE 6 4- Membrane System: • the platelet membrane system consists of : 1. The open canalicular system: its invagination of the plasma membrane. • Its provide both the entry of the external substances into the interior of the platelet and the release of the contents of the granules 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 blood vessel integrity. 2- platelet-platelet interaction( primary hemostatic plug) 3- platelet-coagulation protein interaction( secondary hemostatic plug) 4-Aid in healing injured tissue. 13 February 2023 Platelet and primary hemostasis: Hemostasis: is the property of the circulation that maintains blood as fluid within the blood vessels under normal conditions and the system is able 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 of platelet and plasma coagulation proteins rapidly. activation 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 hemostasis. LECTURE 6 13 February 2023 formation of primary hemosatic plug: •When vessel injury occurs, the platelets react by forming the primary hemostatic plug. •During primary hemostasis platelet the platelet interacts with injured vessels and with each other that resulting in the formation of a primary hemostatic plug. •The formation of a platelet plug requires several activation events including adhesion, shape change, secretion, and aggregation. 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. LECTURE 6 13 February 2023 LECTURE 6 13 February 2023 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. LECTURE 6 13 February 2023 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 LECTURE 6 13 February 2023 4- Platelets aggregation: •The aggregation of Platelets is the joining of Platelets together. •During Platelets adhesion, collagen-binding induces intracellular signaling that activates a specific receptor on the platelets surface, which binds soluble fibrinogen. •fibrinogen may connect two platelets. LECTURE 6 13 February 2023 LECTURE 6