Blood - Leukocytes, Hemostasis - Medical Lecture Slides PDF

Chapter 18 BLOOD Part 2  Leukocytes Five leukocyte types divided into two class Defend against pathogens Contain nucleus and organelles, but not hemoglobin Motility and flexibility —most not in blood but in tissues Diapedesis: process of squeezing through b...

Chapter 18 BLOOD Part 2  Leukocytes Five leukocyte types divided into two class Defend against pathogens Contain nucleus and organelles, but not hemoglobin Motility and flexibility —most not in blood but in tissues Diapedesis: process of squeezing through blood vessel wall Chemotaxis: attraction of leukocytes to chemicals at an infection site  Leukocytes – Granulocytes Neutrophils Most numerous leukocyte in blood First WBC to site of infection/injury Multi-lobed nucleus Cytoplasm has pale granules when stained Enter tissue spaces and phagocytize infectious pathogens Numbers rise dramatically in chronic bacterial infection  Leukocytes – Granulocytes Eosinophils 1–4% of leukocytes Bilobed nucleus connected by thin strand Cytoplasm has reddish granules Phagocytize antigen-antibody complexes or allergens Active in cases of parasitic worm infection  Leukocytes – Granulocytes Basophils 0.5–1% of leukocytes Bilobed nucleus Releases histamine and heparine Histamine release causes increase in blood vessel diameter and capillary permeability (classic allergy symptoms) Heparin release inhibits blood clotting Lymphocytes Reside in lymphatic organs and structures Leukocytes - 20–40% of blood leukocytes Agranulocytes Dark-staining round nucleus Three categories T-lymphocytes manage immune response B-lymphocytes become plasma cells and produce antibodies NK cells (natural killer cells) attack abnormal and infected tissue cells Monocytes C-shaped nucleus 2–8% of blood leukocytes Take up residence in tissues Transform into large phagocytic cells, macrophages Phagocytize bacteria, viruses, debris Summary of Formed Elements Table 17.2 Summary of Formed Elements (continuation) Table 17.2 What did you learn? 9. What is the main function of an erythrocyte, and in what ways is an erythrocyte designed to efficiently carry out its function? 12. What are the differences between type A+ blood and type B− blood? 13. Which type of leukocyte is responsible for creating and releasing antibodies against foreign pathogens? 14. What is the general function of platelets, and what is their life span? 15. Which type of leukocyte is normally the FIRST responder to a site of infection  Hemostasis A series of reactions designed for stoppage of bleeding. During hemostasis, three phases occur in rapid sequence: Vascular spasms – immediate vasoconstriction in response to injury Platelet plug formation Coagulation (blood clotting) Substances involved in coagulation Clotting requires calcium, clotting factors, platelets, vitamin K Clotting factors—most are inactive enzymes Named in order of their discovery (13 total) Factor 1= fibrinogen; factor II = prothrombin etc. Most are produced in the liver Vitamin K A fat-soluble coenzyme required for synthesis of clotting factors II, VII, IX, X Some factors (e.g., factor VII) are Coagulation Pathways – 3 Major Phases Coagulation Pathways Phase 1 – Vascular Spasm Characterized by blood vessel constriction First phase in response to blood vessel injury Limits blood leakage Lasts from few to many minutes Platelets and endothelial cells release chemicals that stimulate further constriction Greater vasoconstriction with greater vessel damage Coagulation Pathways Phase 2 – Platelet Plug Formation Platelets do not normally stick to each other or to the endothelial lining of blood vessels Upon damage to blood vessel endothelium (which exposes collagen) platelets: With the help of von Willebrand factor (VWF) adhere to collagen Are stimulated by thromboxane A2 Stick to exposed collagen fibers and form a platelet plug Release serotonin and ADP, which attract still more platelets The platelet plug is limited to the immediate area of injury by PGI2 Coagulation Pathways Phase 3 – Coagulation A set of reactions in which blood is transformed from a liquid to a gel The final three steps of this series of reactions are: Prothrombin activator is formed Prothrombin is converted into thrombin Thrombin catalyzes the joining of fibrinogen into a fibrin mesh The fibrin mesh is the final product of blood clotting Elimination of the Clot - Fibrinolysis Clot retraction – stabilization of the clot by squeezing serum from the fibrin strands Repair Platelet-derived growth factor (PDGF) stimulates rebuilding of blood vessel wall Fibroblasts form a connective tissue patch Stimulated by vascular endothelial growth factor (VEGF), endothelial cells multiply and restore the endothelial lining Factors Limiting Clot Growth or Formation Two homeostatic mechanisms prevent clots from becoming large Swift removal of clotting factors Inhibition of activated clotting factors Factors Preventing Undesirable Clotting Unnecessary clotting is prevented by the structural and molecular characteristics of endothelial cells lining the blood vessels Platelet adhesion is prevented by: The smooth endothelial lining of blood vessels Heparin and PGI2 (prostaglandin I 2) secreted by endothelial cells What immune cell also secretes heparin? Vitamin E, a potent anticoagulant Hemostasis Disorders: Bleeding Disorders What did you learn? 17. What occurs during a vascular spasm, and how long does this phase last? 18. What prevents platelets from forming plugs in healthy blood vessels? 19. How do platelets serve a central function in all three phases of hemostasis? 20. What is fibrinolysis, and what is its purpose?