Lecture 2 Pathophysiology Part 2 PDF

Blood components and their functions-2 by Dr.Mai Mohammed Hasan Professor of Medical physiology  Platelets (Thrombocytes) Shape: Minute round or oval discs (2-4 ) non-nucleated, size can increase up to 6 µm...

Blood components and their functions-2 by Dr.Mai Mohammed Hasan Professor of Medical physiology  Platelets (Thrombocytes) Shape: Minute round or oval discs (2-4 ) non-nucleated, size can increase up to 6 µm after activation.. Number: 150.000 – 400.000/mm3. Formation: They are formed in the bone marrow as buds on the surface of megakaryocytes and released into the blood under the effect of thrombopoietin from the kidney. Life span: 8-12 days, then removed by tissue macrophage.  Structure of Platelets 1. The outer coat: The platelets have a mucopolysaccharide surface coat, important for adhesion and aggregation of platelets. Glycoproteins bind with the Von Willebrand factor, necessary for platelet adhesion to the damaged endothelial cells and acts as fibrinogen receptors. 2. The plasma membrane: This membrane is the basis structure of platelet factor 3 (PF3). 3. Cytoskeleton under the membrane contains: a- Microfilaments: formed of actin, myosin and thrombasthenin b- Microtubules: which maintains the disc shape of the platelets.  Structure of Platelets 4. Granules: the platelets contain 3 types of granules: a- Dense granules: small, contain nucleotides (ADP) serotonin and calcium. b- Specific (Alpha) granules: large ,contain platelet factors responsible for hemostasis. c- Dense tubular system which contains calcium and may be site of synthesis of prostaglandin and thromboxane A2. It regulate platelet activation by sequestering or releasing calcium 5. The platelets contain mitochondria, glycogen and lysosomes which contain hydrolytic enzymes. Structure of Platelets  Functions of blood platelets 1. Form temporary hemostatic plugs. This is accomplished through platelet adhesion, activation, and aggregation. 2. Release serotonin and thromboxane A2 3. Essential for blood coagulation through supplying platelet factor III and factor XIII. 4. Cause clot retraction. 5. Release platelet-derived growth factor (PDGF) that helps in healing of injured endothelium.  Hemostasis It is stoppage of bleeding by forming blood clots in the wall of damaged blood vessels, and maintenance of blood in a fluid state within the vascular system. it consists of three main components: 1. Vasoconstriction: contraction of the smooth muscle of the vessel wall, a reaction called vascular spasm. 2. platelet aggregation Platelets stick to the exposed collagen fibres of damaged blood vessels and release chemicals that make other platelets in the area clump together to form a platelet plug. Platelet plug is temporary. 3. Coagulation Coagulation (blood clotting) occurs by clotting factors. These are proteins essential for clotting, and most of them are synthesized in the liver. The steps of platelet plug formation  Blood coagulation ▪ Blood coagulation is an important process because platelet aggregation and vasoconstriction are not enough alone to stop bleeding. ▪ The process of coagulation (blood clotting) occurs with the aid of clotting factors. ▪ Coagulation factors are a group of proteins essential for clotting, and most of the clotting factors are synthesized in the liver.  Blood coagulation The clotting stages involve the following: 1. Thromboplastinogenase is an enzyme released by the blood platelets and combines with von Willebrand Factor (vWF) to form thromboplastin. 2. Thromboplastin combines with calcium ions to convert the inactive plasma protein prothrombin into thrombin. 3. Thrombin converts the soluble plasma protein fibrinogen into insoluble plasma protein fibrin. 4. The fibrin threads trap blood cells to form a clot. Two pathways were identified in triggering a blood clot: intrinsic and extrinsic pathways.  Blood coagulation pathways The extrinsic pathway is a rapid clotting system activated when the blood vessels are ruptured and tissue damage takes place. The intrinsic pathway is slower than the extrinsic pathway and is activated when the inner walls of the blood vessels are damaged. Blood coagulation pathways  White Blood Cells (WBC) ▪ WBC circulates in the blood for only a short period of their life span. They spend most of their life migrating through tissues of the body. ▪ All white blood cells migrate from the blood vessel by a process called extravasation. ▪ Some of the white blood cells are capable of phagocytosis and they are neutrophils, eosinophils and monocytes.