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BIOB32H3 (79)


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University of Toronto Scarborough
Biological Sciences
Kenneth Welch

Blood The Cardiovascular System: An Introduction The cardiovascular system •Provides a mechanism for rapid transport of nutrients, waste products, respiratory gases and cells Functions and Composition of Blood Blood •Fluid connective tissue •Functions include •Transporting dissolved gases, nutrients, hormones, and metabolic wastes •Regulating pH and ion composition of interstitial fluids •Restricting fluid loss at injury sites •Defending the body against toxins and pathogens •Regulating body temperature by absorbing and redistributing heat The composition of blood •Plasma and formed elements comprise whole blood •Red blood cells (RBC) •White blood cells (WBC) •Platelets •Can fractionate whole blood for analytical or clinical purposes Hemopoiesis •Process of blood cell formation •Hemocytoblasts are circulating stem cells that divide to form all types of blood cells •Whole blood from anywhere in the body has roughly the same temperature, pH and viscosity Plasma •Accounts for 46-63% of blood volume •92% of plasma is water •Higher concentration of dissolved oxygen and dissolved proteins than interstitial fluid Plasma proteins •more than 90% are synthesized in the liver •Albumins •60% of plasma proteins •Responsible for viscosity and osmotic pressure of blood Additional Plasma Proteins •Globulins •~35% of plasma proteins •Include immunoglobins which attack foreign proteins and pathogens •Include transport globulins which bind ions, hormones and other compounds •Fibrinogen •Converted to fibrin during clotting •Removal of fibrinogen leaves serum Red Blood Cells Abundance of RBCs •Erythrocytes account for slightly less than half the blood volume, and 99.9% of the formed elements •Hematocrit measures the percentage of whole blood occupied by formed elements •Commonly referred to as the volume of packed red cells Structure of RBCs •Biconcave disc, providing a large surface to volume ration •Shape allows RBCs to stack, bend and flex •RBCs lack organelles •Typically degenerate in about 120 days. Hemoglobin •Molecules of hemoglobin account for 95% of the proteins in RBCs •Hemoglobin is a globular protein, formed from two pairs of polypeptide subunits •Each subunit contains a molecule of heme which reversibly binds an oxygen molecule •Damaged or dead RBCs are recycled by phagocytes RBC life span and circulation •Replaced at a rate of approximately 3 million new blood cells entering the circulation per second. •Replaced before they hemolyze •Components of hemoglobin individually recycled •Heme stripped of iron and converted to biliverdin, then bilirubin •Iron is recycled by being stored in phagocytes, or transported throughout the blood stream bound to transferrin RBC Production •Erythropoeisis = the formation of new red blood cells •Occurs in red
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