CHAPTER 19: THE CARDIOVASCULAR SYSTEM: THE BLOOD



Blood: Blood is a specialized connective tissue composed of a liquid extracellular matrix (blood plasma) with blood cells and cell fragments. Blood is slightly alkaline with a pH range between 7.35 – 7.45, and it’s denser and more viscous than water due to the formed elements that compose it. Males, typically, have a blood volume of 5 – 6 liters, whereas females have a blood volume of 4 – 5 liters. For a brief animated explanation of blood, please view: What is Blood?FUNCTIONS AND COMPONENTS OF BLOODFUNCTIONS:1. Transportation: Blood functions to transport various substances throughout the body (i.e. water, ions, glucose, hormones, antibodies, proteins, amino acids, fatty acids, respiratory gases, metabolic wastes).2. Regulation: Blood functions to maintain homeostasis by regulating the pH of body fluids, body temperature, and the fluid volume within fluid compartments (fluid compartments include intracellular and extracellular fluids).3. Protection: Blood functions to protect the body from excessive blood loss via hemostasis and from disease and pathogens via immune responses initiated by PONENTS OF BLOOD:Blood plasma (plasma): Blood plasma is the liquid extracellular matrix of blood, which contains about 90% water and 10% dissolved solutes (i.e. glucose, ions, amino acids, proteins, enzymes, hormones, antibodies, respiratory gases, waste products).Plasma proteins: Plasma proteins include albumins, globulins, fibrinogen, and antibodies (immunoglobulins).Formed elements: The formed elements of blood are the blood cells and cell fragments.181610013779500Erythrocytes: Erythrocytes are red blood cells (RBCs), and they are whole cells.Leukocytes: Leukocytes are white blood cells (WBCs), and they are whole cells.Thrombocytes: Thrombocytes are platelets, and they are cell fragments from megakaryocytes.FORMATION OF BLOOD CELLSHemopoiesis: This is the process of the body producing the formed elements of blood. This process occurs after birth and throughout life.Red bone marrow: Red bone marrow is highly vascularized connective tissue located in spongy bone tissue of the axial skeleton, pectoral and pelvic girdles, humerus, and femur.ERYTHROCYTESErythrocytes = Red blood cells = RBCs: RBCs are whole cells that contain hemoglobin, which is an iron-containing protein that functions to bind to and carry O2 and CO2. Due to the iron, hemoglobin, also, provides RBCs with their red color. Hemoglobin is composed of four subunits: 2 -subunits and 2 -subunits. Each subunit is composed of a heme goup, which contains iron, and the heme groups are the chemical structures that bind to O2 and CO2. Since the hemoglobin molecule is composed of four heme groups, four O2 molecules can bind to each hemoglobin molecule. Approximately 250 million hemoglobin molecules are contained within one RBC, so one RBC can carry approximately 1,000,000,000 O2 molecules!RBC anatomy: RBCs are shaped liked biconcave discs, where the central portion of the cell dips inward. Their cell membranes are strong and flexible, which allows them the ability to change shape without rupturing as they pass through narrow capillaries. Mature RBCs (those that enter the blood supply from the red bone marrow and circulate throughout the body) lack nuclei, so they are unable to perform extensive metabolic reactions, repair the damage they sustain as they circulate, and are incapable of replicating themselves in the blood supply. To watch brief videos of the effect of tonicity on the structure of erythrocytes, please view: Erythrocytes in Isotonic Solution, Erythrocytes in Hypertonic Solution, Erythrocytes in Hypotonic Solution.RBC physiology: RBCs are highly specialized cells that function to transport respiratory gases (O2 and CO2). Due to the lack of a nucleus, all of the internal space of the RBC is available to accommodate the millions of hemoglobin molecules that will transport these gases.RBC life cycle: RBCs live about 120 days in the bloodstream. Since they lack nuclei, RBCs are unable to repair the damage sustained on their cell membranes as they pass through capillaries. So, the damaged RBCs will, eventually, rupture and be removed by the liver and spleen.Erythropoiesis: Erythropoiesis is the process of producing RBCs, which occurs in the red bone marrow. After the RBCs are produced, they pass from the bone marrow into the bloodstream via blood capillaries.LEUKOCYTESLeukocytes = White blood cells = WBCs: WBCs are whole cells that contain a nucleus when mature and do not contain hemoglobin.Granular leukocytes (granulocytes): These leukocytes contain cytoplasmic granules that are visible after staining and using a light microscope.Neutrophils: These cells have small, evenly-distributed granules that stain pale lilac, and the nuclei of these cells typically have two to five lobes connected by thin chromatin strands. The number of nuclear lobes increases as the cell ages. There are approximately 3000-7000 neutrophils per microliter of blood.Eosinophils: These cells contain large uniform-sized granules that stain red-orange with acidic dyes, and the nuclei of these cells typically have two lobes connected by a thick, chromatin strand. There are approximately 100-400 eosinophils per microliter of blood.Basophils: These cells have round, variable-sized granules that stain blue-purple with basic dyes, and the nuclei of these cells typically have two lobes, which are obscured by the granules. There are approximately 20-50 basophils per microliter of blood.Agranular leukocytes (agranulocytes): These leukocytes have cytoplasmic granules that are not visible using a light microscope due to their small size and poor staining qualities.Lymphocytes: The nuclei of these cells are round or slightly indented and stains dark while the cytoplasm stains sky blue forming a rim around the nucleus. More cytoplasm is visible in larger lymphocytes. There are approximately 1500-3000 lymphocytes per microliter of blood.Monocytes: The nuclei of these cells appear kidney-shaped or horseshoe-shaped, and the cytoplasm stains blue-gray and has a foamy appearance. There are approximately 100-700 monocytes per microliter of blood.Macrophages: When monocytes enter tissues from the blood supply, they enlarge and differentiate into macrophages.Functions of WBCs: WBCs, basically, function to defend the body from foreign invaders. However, each type of WBC has a specific function in the body.Neutrophils: Neutrophils function to phagocytize bacteria. For a brief animated explanation of how a neutrophil functions, please view: Neutrophil Function. To watch a video of the action of a typical neutrophil, please view: Neutrophil Chase.Eosinophils: Eosinophils function in immune responses to helminth (parasitic worm) infections.Basophils: Basophils function to release histamine causing inflammation and vasodilation.Lymphocytes: Lymphocytes function to initiate immune responses with antibodies or by directly attacking antigens.Monocytes/Macrophages: Monocytes and macrophages function in phagocytosis of foreign invaders. Monocytes are located in the blood stream, and when they migrate into body tissues, they transition into macrophages.THROMBOCYTESThrombocytes = platelets: Thrombocytes are cell fragments of megakaryocytes. They contain many cytoplasmic vesicles and lack a nucleus. They function in hemostasis. For a brief animated explanation of how thrombocytes are formed, please view: Platelet Formation.4457708890000HEMOSTASISHemostasis: This process involves sequences of responses that are quick and localized to the area of the damaged blood vessels in order to stop bleeding and prevent blood loss. Hemostasis involves three processes: vascular spasm, platelet plug formation, and blood coagulation.Vascular spasm: When a blood vessel is damaged, the immediate response to reduce blood loss from the damaged site is vascular spasm. This response involves contraction of the smooth muscle tissue in the vessel wall, which causes vasoconstriction to decrease the diameter of the blood vessel. When blood-vessel diameter decreases, blood flow through the vessel, also, decreases, which slows and reduces blood loss from the damaged area of the vessel.Platelet plug formation: Platelet plug formation involves the interaction of platelets at damaged sites on blood vessels.STEP 1 – Platelet adhesion: The platelets make contact and stick to the damaged area of the blood vessel.STEP 2 – Platelet release reaction: The platelets begin to interact with each other and release chemicals (i.e. hormones, proteins, enzymes). These chemicals cause vasoconstriction, which decreases blood flow in the vessel.STEP 3 – Platelet aggregation: The platelets continue to become sticky and adhere to the damaged site of the blood vessel. A platelet plug will form as the platelets aggregate at the damaged site.Blood coagulation: Blood coagulation involves a series of enzymatic reactions that causes liquid blood to form into a thick gel. The enzymatic cascade of blood coagulation leads to the development of fibrin protein threads, which traps the formed elements of blood to form blood clots at damaged blood-vessel sites. To watch a brief animated explanation of blood coagulation, please view: Basic Process of Blood Coagulation.1. Common pathway: This step involves the extrinsic pathway in response to tissue trauma and the intrinsic pathway in response to blood trauma (damage to platelets), which will lead to the formation of prothrombinase (enzyme).2. After prothrombinase is formed, it converts prothrombin into thrombin (enzyme).3. Thrombin, then, converts soluble fibrinogen into insoluble fibrin, which will form the threads of the clot.BLOOD GROUPS AND BLOOD TYPESAntigens: These are glycoproteins and glycoplipids that are located on the cell-membrane surface of red blood cells. These molecules provide red blood cells with their identification.Blood groups: Blood groups are based on the presence or absence of RBC antigens. For a brief explanation of the ABO and Rh blood groups, please view: What are Blood Types?Blood types: Blood types are specific types of blood located within a blood group. ABO blood group: This blood group is based on two glycolipid antigens: antigen A and antigen B.Type A: RBCs only have antigen A on their cell-membrane surfaces. Individuals with Type A blood produce anti-B antibodies.Type B: RBCs only have antigen B on their cell-membrane surfaces. Individuals with Type B blood produce anti-A antibodies.Type AB: RBCs have both antigen A and antigen B on their cell-membrane surfaces. Individuals with Type AB blood are the universal recipients, and they do not produce anti-A or anti-B antibodies.Type O: RBCs have neither antigen A nor antigen B on their cell-membrane surfaces. Individuals with Type O blood are the universal donors, and they produce both anti-A and anti-B antibodies.Rh blood group: This blood group is based on specific antigens discovered in the blood of Rhesus monkeys, which are also found in humans. These antigens are referred to as the Rh factor because there 45 different types of Rh antigens, but three of these antigens are common in humans: C, D, and E antigens.Rh+: RBCs have the D antigen on their cell-membrane surfaces. About 85% of Americans are Rh+.Rh-: RBCs do not have any of the Rh antigens on their cell-membrane surfaces. In order for anti-Rh antibodies to form, these individuals must be exposed to Rh+ blood, which causes the immune system to respond by synthesizing anti-Rh antigens. ................
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