erythropoiesis is mediated by erythropoietin which is secreted by the kidneys

Erythropoiesis is mediated by erythropoietin which is

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erythropoiesis is mediated by erythropoietin, which is secreted by the kidneys in response to tissue hypoxia and causes a compensatory increase in erythrocyte production if the oxygen content of the blood decreases because of anemia, high altitude, or pulmonary disease. Iron homeostasis is controlled by hepcidin, a small hormone produced by hepatocytes, which regulates ferroportin, the principal transporter of iron from stores in hepatocytes and macrophages and from intestinal cells that absorb dietary iron. Mechanisms of Hemostasis 1. Hemostasis, or arrest of bleeding, involves (1) vasoconstriction (vasospasm), (2) formation of a platelet plug, (3) activation of the clotting cascade, (4) formation of a blood clot, and (5) clot retraction and clot dissolution. 2. The normal vascular endothelium prevents spontaneous clotting by producing factors such as nitric oxide (NO) and prostacyclin I2 (PGI2) that relax the vessels and prevent platelet activation. 3. Lysis of blood clots is the function of the fibrinolytic system. Plasmin, a proteolytic enzyme, splits fibrin and fibrinogen into fibrin degradation products that dissolve the clot. Aging & Hematologic Value Changes 1. Blood composition changes little with age. Erythrocyte replenishment may be delayed after bleeding, presumably because of iron deficiency. 2. Lymphocyte function appears to decrease with age. Particularly affected is a decrease in cellular immunity. 3. Platelet adhesiveness probably increases with age. Chapter 21: Alterations in Hematologic Function Alterations of Erythrocyte Function Anemia is defined as a reduction in the number or volume of circulating red cells or a decrease in the quality or quantity of hemoglobin. The most common classification of anemias is based on changes in the cell size—represented by the cell suffix -cytic—and changes in the cell’s hemoglobin content—represented by the suffix -chromic. Clinical manifestations of anemia can be found in all organs and tissues throughout the body. Decreased oxygen delivery to tissues causes fatigue, dyspnea, syncope, angina, compensatory tachycardia, and organ dysfunction. Macrocytic (megaloblastic) anemias are characterized by unusually large stem cells in the
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marrow that mature into very large erythrocytes. Macrocytic anemias are caused most commonly by deficiency of vitamin B12. Pernicious anemia, the most common type of macrocytic anemia, can be fatal unless vitamin B12 replacement is given (lifelong replacement is required). Microcytic-hypochromic anemias are characterized by abnormally small red cells with insufficient hemoglobin content. The most common cause is iron deficiency. *Iron deficiency anemia is the most common type of anemia worldwide and usually develops slowly, with a gradual, insidious onset of symptoms, including fatigue, weakness, dyspnea, alteration of various epithelial tissues, and vague neuromuscular complaints. Iron deficiency anemia is usually a result of a chronic blood loss or decreased iron intake. Once the source of blood loss is
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