Chapter 19 Composition of Blood Blood is the body s only fluid tissue It is composed of liquid plasma and formed elements Formed elements include Erythrocytes or red blood cells RBCs Leukocytes or white blood cells WBCs Platelets Hematocrit the percentage of RBCs out of the total blood volume Physical Characteristics and Volume Blood is a sticky opaque fluid with a metallic taste Color varies from scarlet to dark red The pH of blood is 7 35 7 45 Temperature is 38 C Blood accounts for approximately 8 of body weight Average volume 5 6 L for males and 4 5 L for females Functions of Blood Blood performs a number of functions dealing with Substance distribution Regulation of blood levels of particular substances Body protection Distribution Blood transports Oxygen from the lungs and nutrients from the digestive tract Metabolic wastes from cells to the lungs and kidneys for elimination Hormones from endocrine glands to target organs Regulation Blood maintains Appropriate body temperature by absorbing and distributing heat Normal pH in body tissues using buffer systems Adequate fluid volume in the circulatory system Protection Blood prevents blood loss by Activating plasma proteins and platelets Initiating clot formation when a vessel is broken Blood prevents infection by Synthesizing and utilizing antibodies Activating complement proteins Activating WBCs to defend the body against foreign invaders Blood Plasma Blood plasma contains over 100 solutes including Proteins albumin globulins clotting proteins and others Lactic acid urea creatinine Organic nutrients glucose carbohydrates amino acids Electrolytes sodium potassium calcium chloride bicarbonate Respiratory gases oxygen and carbon dioxide Functions Transport of The products of digestion Carbon dioxide Hormones Vitamins Urea Heat Formed Elements of blood plasma Erythrocytes leukocytes and platelets make up the formed elements Only WBCs are complete cells RBCs have no nuclei or organelles and platelets are just cell fragments Most formed elements survive in the bloodstream for only a few days Most blood cells do not divide but are renewed by cells in bone marrow Erythrocytes RBCs Biconcave discs anucleate essentially no organelles Filled with hemoglobin Hb a protein that functions in gas transport Contain the plasma membrane protein spectrin and other proteins that Give erythrocytes their flexibility Allow them to change shape as necessary Erythrocytes RBCs Erythrocytes are an example of the complementarity of structure and function Structural characteristics contribute to its gas transport function Biconcave shape has a huge surface area relative to volume Erythrocytes are more than 97 hemoglobin ATP is generated anaerobically so the erythrocytes do not consume the oxygen they transport Erythrocyte Function RBCs are dedicated to respiratory gas transport Hb reversibly binds with oxygen and most oxygen in the blood is bound to Hb Hb is composed of the protein globin made up of two alpha and two beta chains each bound to a heme group Each heme group bears an atom of iron which can bind to one oxygen molecule Each Hb molecule can transport four molecules of oxygen Production of Erythrocytes Hematopoiesis blood cell formation Hematopoiesis occurs in the red bone marrow of the Axial skeleton and girdles Epiphyses of the humerus and femur Hemocytoblasts give rise to all formed elements Production of Erythrocytes Erythropoiesis The developmental pathway consists of three phases 1 ribosome synthesis in early erythroblasts 2 Hb accumulation in late erythroblasts and normoblasts 3 ejection of the nucleus from normoblasts and formation of reticulocytes Reticulocytes then become mature erythrocytes Hemoglobin Hb Oxyhemoglobin Hb bound to oxygen Oxygen loading takes place in the lungs Deoxyhemoglobin Hb after oxygen diffuses into tissues reduced Hb Carbaminohemoglobin Hb bound to carbon dioxide Carbon dioxide loading takes place in the tissues Regulation and Requirements for Erythropoiesis Circulating erythrocytes the number remains constant and reflects a balance between RBC production and destruction Too few RBCs leads to tissue hypoxia Too many RBCs causes undesirable blood viscosity Erythropoiesis is hormonally controlled and depends on adequate supplies of iron amino acids and B vitamins Hormonal Control of Erythropoiesis Erythropoietin EPO release by the kidneys is triggered by Hypoxia due to decreased RBCs Decreased oxygen availability Increased tissue demand for oxygen Enhanced erythropoiesis increases the RBC count in circulating blood Oxygen carrying ability of the blood Fate and Destruction of Erythrocytes The life span of an erythrocyte is 100 120 days Old RBCs become rigid and fragile and their Hb begins to degenerate Dying RBCs are engulfed by macrophages Heme and globin are separated and the iron is salvaged for reuse Heme is degraded to a yellow pigment called bilirubin The liver secretes bilirubin into the intestines as bile The intestines metabolize it into urobilinogen This degraded pigment leaves the body in feces in a pigment called stercobilin Globin is metabolized into amino acids and is released into the circulation Hb released into the blood is captured by haptoglobin and phgocytized Erythrocyte Disorders Anemia blood has abnormally low oxygencarrying capacity It is a symptom rather than a disease itself Blood oxygen levels cannot support normal metabolism Signs symptoms include fatigue paleness shortness of breath and chills Anemia Insufficient Erythrocytes Hemorrhagic anemia result of acute or chronic loss of blood Hemolytic anemia prematurely ruptured RBCs Aplastic anemia destruction or inhibition of red bone marrow Anemia Decreased Hemoglobin Content Iron deficiency anemia results from A secondary result of hemorrhagic anemia Inadequate intake of iron containing foods Impaired iron absorption Pernicious anemia results from Deficiency of vitamin B12 Lack of intrinsic factor needed for absorption of B12 Treatment is intramuscular injection of B12 application of Nascobal Anemia Abnormal Hemoglobin Thalassemias absent or faulty globin chain in Hb RBCs are thin delicate and deficient in Hb Sickle cell anemia results from a defective gene coding for an abnormal Hb called hemoglobin S HbS HbS has a single amino acid substitution in the beta chain This defect causes RBCs to become sickle shaped in low oxygen situations Polycythemia Polycythemia excess RBCs that increase blood viscosity Three main polycythemias are
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