Chapter 18: Cardiovascular System: The Blood PDF

Chapter 18: The Cardiovascular System: The Blood Suggested Lecture Outline I. INTRODUCTION A. The cardiovascular system consists of three interrelated components: blood, the heart, and blood vessels. B. To obtain nutrients and remove wastes, cells must be serviced by blood and...

Chapter 18: The Cardiovascular System: The Blood Suggested Lecture Outline I. INTRODUCTION A. The cardiovascular system consists of three interrelated components: blood, the heart, and blood vessels. B. To obtain nutrients and remove wastes, cells must be serviced by blood and interstitial fluid. 1. Blood, a connective tissue, is composed of plasma and formed elements. 2. Interstitial fluid is the extracellular fluid that bathes body cells. II. BLOOD CONTAINS PLASMA AND FORMED ELEMENTS AND TRANSPORTS ESSENTIAL SUBSTANCES THROUGH THE BODY. A. Functions of Blood 1. Blood has three general functions; transportation, regulation, and protection a. Blood transports oxygen, carbon dioxide, nutrients, heat, wastes, and hormones. b. It helps regulate pH, body temperature, and water content of cells. c. It prevents blood loss through clotting and combats toxins and microbes through certain phagocytic white blood cells or specialized plasma proteins. B. Physical Characteristics of Blood 1. Physical characteristics of blood include a viscosity greater than that of water; temperature, 38oC (100.4o); and a pH of 7.35 to 7.45. Blood color varies with oxygen content. CHAPTER 18- DR PARIA PARTO 1  2. Blood constitutes about 8% of body weight; volume ranges from 4 to 6 liters. C. Clinical Connection: Withdrawing Blood Blood samples are obtained via venipuncture. A common site for venipuncture is the median cubital vein. Another method is through a finger or heel stick. In an arterial stick blood is withdrawn from an artery. D. Components of Blood 1. Blood consists of 55% plasma and 45% formed elements. If a sample of blood is centrifuged the formed elements sink to the bottom and the plasma forms a layer on top. WBCs and platelets form a thin layer called the buffy coat.. 2. Blood plasma consists of 91.5% water and 8.5% solutes. a. Principal solutes include plasma proteins (albumins, globulins, and fibrinogen), nutrients, enzymes, hormones, respiratory gases, electrolytes, and waste products. 3. Formed Elements a. The formed elements in blood include erythrocytes (red blood cells or RBCs), leukocytes (white blood cells or WBCs), and thrombocytes (platelets). b. The percentage of total blood volume occupied by red blood cells is called the hematocrit. A hematocrit measures the percentage of red blood cells in whole blood. Adult males have a higher hematocrit than females, largely due to testosterone, which stimulates synthesis of erythropoietin (EPO). c. A significant drop in hematocrit indicates anemia, due to a lower than normal number of RBCs. d. In polycythemia, the percentage of RBC is abnormally high with a higher than normal hematocrit. This increases the viscosity of the blood. III. HEMOPOIESIS IS THE PRODUCTION OF FORMED ELEMENTS. CHAPTER 18- DR PARIA PARTO 2  A. Blood cells are formed from pluripotent hematopoietic stem cells. 1. Hemopoiesis or hematopoiesis is the process of developing formed elements of the blood. It mainly occurs in the red bone marrow. 2. Originating from the pluripotent stem cells are the myeloid stem cells and lymphoid stem cells. a. Myeloid stem cells give rise to RBCs, platelets, and all WBCs except for lymphocytes. b. Lymphoid stem cells give rise to lymphocytes. 3. Myeloid and lymphoid stem cells differentiate into precursor cells known as blast cells that will develop into the specific elements of blood. 4. Several hormones called hemopoietic growth factors regulate the differentiation and proliferation of formed elements. Erythropoietin (EPO) produced by the kidneys increases the number of red blood cell precursors. Thrombopoietin is produced by the liver and stimulates the formation of platelets from megakaryocytes. Some cytokines stimulate white blood cell formation. IV. MATURE RED BLOOD CELLS ARE BICONCAVE CELLS CONTAINING HEMOGLOBIN. A. Red blood cells (RBCs) contain the oxygen-carrying protein hemoglobin and number about 5.4 million cells/microliter of blood in a healthy male B. RBC Anatomy 1. RBCs are biconcave discs without nuclei that contain hemoglobin and lack a nucleus and other organelles. 2. The cell membrane is strong yet flexible which allows the cells to deform without rupturing as they squeeze through narrow capillaries. C. RBC Physiology CHAPTER 18- DR PARIA PARTO 3  1. The function of the hemoglobin in RBCs is to transport oxygen and some carbon dioxide. Hemoglobin molecules are specialized components of the red blood cell plasma membrane that combine with oxygen or with carbon dioxide in this transport process. 2. Each hemoglobin molecule consists of globin and four heme groups, each heme contains an iron (Fe2+) that can combine with one oxygen molecule. V. RED BLOOD CELLS HAVE A LIFE CYCLE OF 120 DAYS. A. Red blood cells only live about 120 days because of the wear and tear on their plasma membranes as they squeeze through blood capillaries. They cannot undergo mitosis since they lack a nucleus and organelles. B. RBC are removed from circulation and destroyed by macrophages in the spleen and liver. The RBC is split apart and the globin portion is broken down into amino acids and reused for protein synthesis. C. The iron in the heme portion is removed and associates with transferrin which carries it to the red bone marrow where it is used in hemoglobin synthesis. D. The non-iron portion of heme is converted into biliverdin and then into bilirubin which is transported to the liver. In the large intestine bacteria convert bilirubin into urobilinogen. E. Some urobilinogen is absorbed back into the blood and converted into urobilin and excreted in the urine. Most urobilinogen is eliminated in the feces in the form of a brown pigment called stercobilin. VI. ERYTHROPOIESIS IS THE PROCESS OF RED BLOOD CELL FORMATION. A. RBC production, called erythropoiesis, occurs in adult red bone marrow of certain bones. It begins with a proerythroblast which divides several times producing cells, to ultimately form a reticulocyte, which enters the bloodstream. Reticulocytes develop into erythrocytes within CHAPTER 18- DR PARIA PARTO 4  1 or 2 days after they leave the red bone marrow. The main stimulus for erythropoiesis is hypoxia. Hypoxia stimulates the kidneys to release EPO. B. Clinical Connection: Reticulocyte Count The rate of erythropoiesis is measured by a reticulocyte count. A low “retic” count may indicate a shortage of EPO or an inability of the red bone marrow to respond to it. VII. BLOOD IS CATEGORIZED INTO GROUPS BASED ON SURFACE ANTIGENS. A. The surfaces of red blood cells contain genetically determined blood group antigens, called agglutinogens. 1. Blood is categorized into different blood groups based on the presence or absence of various antigens. 2. Within a blood group there may be two or more different blood types. B. ABO Group 1. In the ABO system, agglutinogens (antigens) A and B determine blood types 2. Plasma contains agglutinins (antibodies), designated as anti-A antibody and anti-B antibody, that react with agglutinogens that are foreign to the individual. C. Transfusions 1. Knowledge of blood types is essential to safe transfusion of blood. 2. In an incompatible blood transfusion antibodies in the recipient’s plasma bind to the antigens on the donated RBCs which causes agglutination. Formation of these antigen-antibody complexes causes hemolysis. D. Rh Blood Group 1. In the Rh system, individuals whose erythrocytes have Rh agglutinogens are classified as Rh+. Those who lack the antigen are Rh-. E. Typing and Cross-Matching Blood for Transfusion 1. ABO blood can be typed by mixing with different antisera CHAPTER 18- DR PARIA PARTO 5  2. Cross-match is the process of mixing the donor’s blood with the patient’s blood to determine if agglutination occurs. If it occurs it is positive for the antigen in the sample. VIII. WHITE BLOOD CELLS COMBAT INFLAMMATION AND INFECTION. A. Leukocytes (white blood cells or WBCs) are nucleated cells and do not contain hemoglobin. Two principal types are granular (neutrophils, eosinophils, basophils) and agranular (lymphocytes and monocytes) B. Granular leukocytes and monocytes develop from myeloid stem cells while lymphocytes develop from lymphoid stem cells C. WBC Types 1. Granular leukocytes include eosinophils, basophils, and neutrophils (polymorphonuclear leukocytes or PMNs) based on the straining of the granules. 2. Agranular leukocytes do not have cytoplasmic granules and include the lymphocytes and monocytes, which differentiate into macrophages (fixed and wandering). D. WBC Functions 1. The general function of leukocytes is to combat inflammation and infection. a. WBCs leave the blood stream by emigration. Molecules known as adhesion molecules help WBCs stick to the endothelium. One example are selectins which stick to the surface of neutrophils causing them to slow down and roll along the endothelial surface. The neutrophil contains other adhesion molecules known as integrins which secure it to the endothelium and assist its movement through the capillary wall. b. Some WBCs, particularly neutrophils and macrophages, are active in phagocytosis. CHAPTER 18- DR PARIA PARTO 6  c. The chemical attraction of WBCs to a disease or injury site is termed chemotaxis. d. Different WBCs combat inflammation and infection in different ways. 1) Neutrophils and wandering or fixed macrophages (which develop from monocytes) do so through phagocytosis. Neutrophils release several destructive chemicals such as lysozyme, hydrogen peroxide, and defensins. 2) Eosinophils release histaminase to combat the effects of histamine in allergic reactions, phagocytize antigen-antibody complexes, and combat parasitic worms. 3) Basophils develop into mast cells that liberate heparin, histamine, and serotonin in allergic reactions that intensify the inflammatory response. 4) B cells (lymphocytes) are particularly effective in destroying bacteria and inactivating their toxins, and are responsible for transfusion reactions and allergies. T cells (lymphocytes) attack infected body cells, tumor cells, and are responsible for the rejection of transplanted organs. 5) NK cells attack a wide variety of infected body cells and certain tumor cells. E. WBC Lifespan 1. White blood cells usually live for only a few hours or a few days. Normal blood contains 5,000-10,000 WBCs/µL. a. Leukocytosis refers to an increase in the number of WBCs. b. Leukopenia refers to an abnormally low number of WBCs. CHAPTER 18- DR PARIA PARTO 7  2. A differential white blood cell count is a diagnostic test in which specific white blood cells are enumerated. Because each type of WBC plays a different role, determining the percentage of each type in the blood assists in diagnosing the condition. IX. PLATELETS REDUCE BLOOD LOSS FROM DAMAGED VESSELS. A. Thrombopoietin stimulates myeloid stem cells to produce platelets. 1. Myeloid stem cells develop into megakaryoblasts 2. Megakaryoblasts transform into megakaryocytes which fragment. 3. Each fragment, enclosed by a piece of cell membrane, is a platelet (thrombocyte). B. Normal blood contains 150,000 to 400,000 platelets/µL. Platelets have a life span of only 5 to 9 days; aged and dead platelets are removed by fixed macrophages in the spleen and liver. C. Platelets help stop blood loss from damaged vessels by forming a platelet plug. Their granules also contain chemicals that promote blood clotting. D. Table 18.5 summarizes the formed elements in blood. E. Clinical Connection: Complete Blood Count (CBC) A CBC is a valuable test that screens for anemia and various infections. XI. HEMOSTASIS IS THE SEQUENCE OF EVENTS THAT STOPS BLEEDING FROM A DAMAGED BLOOD VESSEL. A. Hemostasis refers to the stoppage of bleeding. When blood vessels are damaged or ruptured, the hemostatic response must be quick, localized to the region of damage, and carefully controlled. B. It involves vascular spasm, platelet plug formation, and blood coagulation (clotting). C. Vascular Spasm CHAPTER 18- DR PARIA PARTO 8  1. In vascular spasm, the smooth muscle of a blood vessel wall contracts to reduce blood loss. D. Platelet Plug Formation 1. Platelet plug formation involves the clumping of platelets around the damage to stop the bleeding. Platelets become activated and release the contents of their vesicles, this is called the platelet release reaction. The resulting platelet adhesion and aggregation results in the platelet plug. 2. Initially the plug is loose, it becomes tighter when reinforced from fibrin threads during blood clotting. E. Blood Clotting 1. A clot is a gel consisting of a network of insoluble protein fibers (fibrin) in which formed elements of blood are trapped. The process of gel formation is called clotting or coagulation. 2. The chemicals involved in clotting are known as clottingfactors; most are in blood plasma, some are released by platelets, and one is released from damaged tissue cells. a. The clotting cascade can be initiated by either the extrinsic pathway or the intrinsic pathway. b. Blood clotting involves a cascade of reactions that may be divided into three stages: formation of prothrombinase, conversion of prothrombin into thrombin, and conversion of soluble fibrinogen into insoluble fibrin c. The extrinsic pathway (Figure 18.13a) occurs rapidly and is named because a tissue protein called tissue factor leaks into the blood from damaged tissue cells outside (extrinsic to) blood vessels. d. The intrinsic pathway (Figure 18.13b) is more complex and occurs more slowly. Its activators are in direct contact or within (intrinsic to) the blood. CHAPTER 18- DR PARIA PARTO 9  e. The common pathway begins with the formation of prothrombinase (Figure 18.13c). Ca2+ and prothrombinase catalyze the conversion of prothrombin to thrombin. Thrombin has two positive feedback effects. First it accelerates the formation of prothrombinase and second it activates platelets. As the positive feedback loop continues, the fibrin clot grows. f. Clot retraction is the consolidation or tightening of the fibrin clot. F. Hemostatic Control Mechanisms 1. Even when blood vessels are not damaged, small clots begin to form many times a day. Usually small inappropriate clots dissolve via fibrinolysis. When a clot is formed an inactive plasma enzyme, plasminogen, is incorporated into the clot. When plasminogen is activated into plasmin it can dissolve the clot. 2. Substances that inhibit coagulation, called anticoagulants, are also present in blood. An example is heparin. G. Clotting in Blood Vessels 1. Despite the action of anticoagulants and fibrinolysis, blood clots sometimes form within blood vessels. 2. Clotting in an unbroken blood vessel is called thrombosis. 3. A thrombus (clot), bubble of air, fat from broken bones, or piece of debris transported by the bloodstream that moves from its site of origin is called an embolus. 4. Clinical Connection: Anticoagulants Patients who are at increased risk of forming blood clots receive anticoagulants. Examples are heparin or warfarin (Coumadin). Warfarin acts as an antagonist to vitamin K and blocks the synthesis of four clotting factors. To prevent clotting in donated blood, blood banks and laboratories often add substances that remove Ca2+; examples include EDTA and CPD. CHAPTER 18- DR PARIA PARTO 10