BLOOD

1. BLOOD CHAPTER 19

2. Introduction • The major organs and tissues of the cardiovascular system are blood, heart and blood vessels-arteries, veins and capillaries. • The cardiovascular system provides a mechanism for the rapid transport of nutrients, waste products, respiratory gases and cells within the body.

3. Composition and Functions of Blood • Blood is composed of formed elements and plasma, which together make up whole blood. • The formed elements are red blood cells, white blood cells and platelets. Plasma accounts for about 55% of the volume of blood and is 92% water. Whole blood can be fractionated. • Blood is a specialized connective tissue. Functions are: • transporting substances • regulating pH and electrolyte balance • restricting fluid losses • defending the body • regulating body temperature

4. Blood Plasma • Plasma is a straw-colored, viscous fluid composed of 92% water. The remaining 8% is solutes such as nutrients, gases, slats, hormones, and proteins. • Compared with interstitial fluid plasma has a highest dissolved oxygen conc. And more dissolved proteins. • There are three primary classes of plasma proteins: • albumin-constitute 60% of plasma proteins. Imp. Blood buffer • globulins-35%. Include immunoglobulins, transport globulins • fibrinogen-converted to fibrin in the clotting reaction. Removal of this from plasma leaves a fluid called serum.

5. Formed Elements • Hemopoieseis is the process of formation of blood cells. Circulating stem cells called hemocytoblats divide to form all types of blood cells. • Red blood cells or Erythrocytes: small biconcave cells. these account for slightly less than half the blood volume and 99% of the formed elements. The hematocrit value indicates the percentage of whole blood occupied by formed elements. • RBC’s transport oxygen and carbon dioxide within the blood stream. They are highly specialized cells with a large surface area. Die after 120 days. Damaged or dead RBC’s are recycled by phagocytes.

6. Erythrocytes • Molecules of hemoglobin (Hb) account for over 95% of RBC’s proteins. It is a globular protein formed from two pairs of polypeptide subunits. Each subunit contains a single molecule of heme which reversibly binds an oxygen molecule. In the lungs oxygen binds to iron atoms in hemoglobin to produce oxyhemoglobin. In body tissues, oxygen dissociates from iron , producing deoxyhemoglobin. • Iron vitamin B12 and folic acid are essential for production of hemoglobin.

7. Erythropoiesis • Erythropoiesis-occurs mainly within the red bone marrow. Formation increases under the stimulation by erythropoietin and testosterone. • Red blood cells begin as hemocytoblasts and proceed through proerythroblast stage to the erythroblast, normoblast to reticulocyte stages. During this stage hemoglobin accumulates and organelles and nucleus are extruded. Differentiation of reticulocytes is complete in the blood stream. • .

8. Erythrocytes • Erythrocyte disorders include anemia and polycythemia. • Blood type is determined by the presence or absence of specific surface antigens called agglutinogens: A, B, and Rh (D). Antibodies (agglutinins) in plasma react to antigens.

9. Leukocytes • WBC’s or leukocytes defend the body against pathogens and remove toxins, wastes and abnormal or damaged cells. All are nucleated. • Leukocytes exhibit diapedesis( the ability to move through vessel walls) and chemotaxis (attraction to specific chemicals). • Granular leukocytes(granulocytes) are subdivided into neutrophils, basophils and eosinophils.

10. Leukocytes • Granulocytes: 50-70% of WBC’s are neutrophils which are highly mobile phagocytes. The much less common eosinophils are also phagocytes. The relatively rare basophils migrate to damaged tissues and release histamine and heparin, aiding the inflammation response. • Agranular leukocytes (agranulocytes)-divide into monocytes and lymphocytes. Monocytes migrating into peripheral tissues become tissue macrophages. Lymphocytes, the primary cells of the lymphatic system, include T cells -attack foreign cells-, B cells-produce antibodies, NK cells-destroy abnormal tissue cells.

11. Leukocytes • Granulocytes and monocytes are produced by the stem cells in the bone marrow. Stem cells responsible for lymphopoiesis also originate in the bone marrow, but many migrate to lymphoid tissues. • Factors that regulate lymphocyte maturation are not completely understood. Regulated by colony-stimulating factors. (CSF’s) and interleukins released mainly by macrophages and lymphocytes. • Leukocyte disorders-leukemias and infectious mononucleosis.

12. Platelets • Megakaryocytes in the bone marrow release packets of cytoplasm (platelets) into the circulating blood. • The functions of platelets include: • transporting chemicals important to the clotting process • forming a temporary patch in the walls of damaged blood vessels • contracting after a clot has formed.

13. Hemostasis • The process of hemostasis prevents the loss of blood through the walls of damaged vessels. • The vascular phase: period of local vasoconstriction resulting from vascular spasm at the injury site. • The platelet phase: follows as platelets are activated, aggregate at the site and adhere to the damaged surfaces. • The coagulation phase: occurs as factors released by platelets and endothelial cells interact with clotting factors to form a blood clot.

14. Hemostasis • Clot retraction: platelets contract and pull the torn edges of the damaged vessel closer together. • Fibrinolysis: here the clot gradually dissolves through the action of plasmin, the activated form of circulating plasminogen. • Manipulation of hemostasis: clotting may be prevented by administering drugs that depress the clotting response or dissolve existing clots. Important anticoagulant drugs include heparin, dicumarol, t-PA, coumadin, streptokinase, urokinase and aspirin.

15. Coagulation • This may be initiated by either the intrinsic or extrinsic pathway. • Tissue facto (thromboplastin) allows the extrinsic pathway to bypass many of the steps in intrinsic pathway. • A series of procoagulants oversees the intermediate steps of each cascade. • The pathways converge as prothrombin is converted to thrombin.

16. Disorders of hemostasis • Thromoboembolytic disorders: undesirable clot formation • Thrombocytopenia-a deficit of platelets, causes spontaneous bleeding. Hemophilia. Liver disease can cause this because the liver manufactures many of the coagulation proteins.