Chapter 17 Blood Overview Blood Composition Functions Components o Blood is the only fluid tissue in the body o Has both cellular and liquid components o Specialized type of connective tissue in which living blood cells the formed elements are suspended in a nonliving fluid matrix called plasma o Collagen and elastic fibers are absent from blood BUT dissolved fibrous PRO become visible as fibrin strands during blood clotting o Erythrocytes RBC that transport O2 A thin whitish layer called the buffy coat is present at the erythrocyte plasma junction This layer contains leukocytes the WBC that act in various ways to protect the body platelets cell fragments that help stop bleeding Erythrocytes normally constitute about 45 of the total volume of a blood sample a percentage known as the hematocrit Normal hematocrit values vary o Males 47 5 o Females 42 5 o If you were to centrifuge blood after centrifugation erythrocytes would sink to the bottom of the test tube 45 of whole blood Leukocytes platelets 1 of whole blood A Layer of buffy coat The upper most layer lightest would be plasma 55 of whole blood Physical Characteristics Volume element s o Blood is more dense than water and about 5x more viscous largely b c of its formed o Slightly alkaline with a pH btw 7 35 7 45 its temperature 38 C or 100 4 F is always slightly higher than body temp o Blood accounts for approx 8 of body weight Avg volume in healthy adult males 5 6 L Healthy adult females 4 5 L Functions o Distribution Delivering Oxygen from the lungs and nutrients from the digestive tract to all body cells Transporting metabolic waste products from cells to elimination sites to the lungs for elimination of carbon dioxide to the kidneys for disposal of nitrogenous wastes in urine 1 Transporting hormones from the endocrine organs to their target organs o Regulation Maintaining appropriate body temp by absorbing distributing heat throughout the body to the skin surface to encourage heat loss Maintain normal pH in body tissues Many blood proteins and other blood borne solutes act as buffers to prevent excessive or abrupt changes in blood Ph that could jeopardize normal cell activities Additionally blood acts as the reservoir for the body s alkaline reserve of bicarbonate atoms Maintain adequate fluid volume in the circulation system Salts and other blood PRO act to repvent excessive fluid loss from the bloodstream into the tissue spaces As a result the fluid volume in the blood vessels remains ample to support efficient blood circulation to all parts of the body Preventing blood loss When a blood vessel is damaged platelets plasma PRO initiate clot formation halting blood loss Preventing infection Drifting along in the blood are antibodies complement PRO WBC all of which help defend the body against foreign invaders such as bacteria and viruses o Protection Blood Plasma Blood plasma is a straw colored sticky fluid Mostly water 90 Plasma PRO o Account for 8 by weight of plasma volume o Most abundant o Most are produced by liver EXCEPT hormones gamma globulins o Are NOT taken up by cells to be used as fuels or metabolic nutrients as are most other plasma solutes i e glucose FA o Albumin 60 of plasma PRO Acts as a carrier to shuttle certain molecules through the circulation important blood buffer major blood PRO contributing to the plasma osmotic pressure Formed Elements Formed elements erythrocytes abundant leukocytes platelets Unusual features o 2 3 are not even TRUE cells Erthryocytes have no nuclei or organelles platelets are cell fragments Only leukocytes are complete cells o Most of the formed elements survive in the bloodstream for a few days 2 o Most blood cells don t divide they are continuously renewed by division of cells in bone marrow where they originate Erythrocytes o Structural Characteristics o Function Also called RBC Small cells about 7 5 m in diameter Mature erythrocytes are bound by a plasma membrane but lack a nucleus have essentially no organelles Spectrin maintains bioconcave shape of RBC Erythrocytes are more than 97 hemoglobin ATP is generated anaerobically so the erythrocytes don t consume the oxygen they transport Major factor contributing to blood viscosity 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 Oxyhemoglobin Hb bound to oxygen Oxygen loading takes place in the lungs Carbaminohemoglobin Hb bound to carbon dioxide Carbon dioxide loading takes place in the tissues Deoxyhemoglobin Hb after oxygen diffuses into tissues reduced Hb 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 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 formation of reticulocytes Reticulocytes then become mature erythrocytes o Production 3 Regulation Requirements for Erythropoiesis o Circulating eryhtrocytesis constant and reflects a balance btw RBC production and destruction Balance is imp b c too erythrocytes leads to tissue hypoxia O deprivation whereas too many makes the blood undesirably viscous o New cells are produced incredibly fast in order to ensure that the of erythrocytes in blood remains within the homeostatic range Process is controlled hormonally depends on adequate supplies of iron AA and some B vitamins o Hormonal Controls Direct stimulus for erythrocyte formation is provided by erythropoietin EPO a glycoPRO hormone Liver produces some EPO but kidney is the major role in EPO production When certain kidney cells become hypoxic inadequate O they accelerate their release of erythropoietin The drop in normal blood O levels that triggers EPO formation can result from o Reduced of RBC due to hemorrhage or excessive RBC destruction o Insufficient hemoglobin RBC ex iron deficiency o educed availability of O as might occur at high altitudes or Imbalance Normal blood oxygen levels during pneumonia O2 carrying ability of blood Imbalance Reduces O2 levels in blood Start Stimulus Hypoxia due to decreased RBC count decreased
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