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FSU PET 3322 - Chapter 19 Composition of Blood

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Chapter 19Composition 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 femalesFunctions of Blood Blood performs a number of functions dealing with: _ Substance distribution _ Regulation of blood levels of particular substances _ Body protectionDistribution 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 organsRegulation Blood maintains: _ Appropriate body temperature by absorbing and distributing heat _ Normal pH in body tissues using buffer systems _ Adequate fluid volume in the circulatory systemProtection 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 againstforeign invadersBlood 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 dioxideFunctions: Transport of:  The products of digestion  Carbon dioxide  Hormones  Vitamins  Urea HeatFormed 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 marrowErythrocytes (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 necessaryErythrocytes (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 transportErythrocyte 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 oxygenProduction 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 elementsProduction of Erythrocytes: ErythropoiesisThe developmental pathway consists of threephases_ 1 – ribosome synthesis in early erythroblasts_ 2 – Hb accumulation in late erythroblasts andnormoblasts_ 3 – ejection of the nucleus from normoblasts andformation of reticulocytes_ Reticulocytes then become mature erythrocytesHemoglobin (Hb)Oxyhemoglobin – Hb bound to oxygen_ Oxygen loading takes place in the lungs_ Deoxyhemoglobin – Hb after oxygen diffuses intotissues (reduced Hb)_ Carbaminohemoglobin – Hb bound to carbondioxide_ Carbon dioxide loading takes place in the tissuesRegulation and Requirements for Erythropoiesis_ Circulating erythrocytes – the number remainsconstant and reflects a balance between RBCproduction and destruction_ Too few RBCs leads to tissue hypoxia_ Too many RBCs causes undesirable bloodviscosity_ Erythropoiesis is hormonally controlled anddepends on adequate supplies of iron, amino acids,and B vitaminsHormonal Control of ErythropoiesisErythropoietin (EPO) release by the kidneys istriggered 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 bloodFate and Destruction of ErythrocytesThe life span of an erythrocyte is 100–120 days_ Old RBCs become rigid and fragile, and their Hbbegins to degenerate_ Dying RBCs are engulfed by macrophages_ Heme and globin are separated and the iron issalvaged for reuseHeme is degraded to a yellow pigment calledbilirubin_ The liver secretes bilirubin into the intestines as bile_ The intestines metabolize it into urobilinogen_ This degraded pigment leaves the body in feces, in apigment called stercobilinGlobin is metabolized into amino acids and isreleased into the circulation_ Hb released into the blood is captured byhaptoglobin and phgocytizedErythrocyte DisordersAnemia – blood has abnormally low oxygencarryingcapacity_ It is a symptom rather than a disease itself_ Blood oxygen levels cannot support normalmetabolism_ Signs/symptoms include fatigue, paleness,shortness of breath, and chillsAnemia: Insufficient ErythrocytesHemorrhagic anemia – result of acute or chronicloss of blood_ Hemolytic anemia – prematurely ruptured RBCs_ Aplastic anemia – destruction or inhibition of redbone marrowAnemia: Decreased Hemoglobin ContentIron-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


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