Describe the composition of blood, function and lifespan of each cell type, and the process of erythropoiesis. Blood consists of plasma containing water, organic and inorganic solutes, and both red (erythrocytes) and white cells (Cytopenia; Applegate, 2000, 229-233). Erythrocytes contain hemoglobin which transports oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs. Their lifespan is approximately 120 days. Erythrocyte production is controlled by a negative feedback mechanism by the hormone erythropoietin, which is produced by the liver and activated by renal erythropoietic factor from the kidneys, which stimulates the red bone marrow to produce erythrocytes. The white cells (lifespan 1-3 days) consist of neutrophils (phagocytes), eosinophils (involved in allergic reactions and destruction of parasitic worms), basophils (contain histamine and the anticoagulant heparin), lymphocytes (involved in immune response), monocytes (phagocytes, become macrophages on leaving bloodstream), and thrombocytes (platelets, involved in blood clotting, lifespan 10 days).
Compare the characteristics of the following forms of anemia:
-iron deficiency anemia is caused by most commonly by blood loss (Berkow, Beers and Fletcher, 1997, 743) - may be due to dietary deficiency in infants and small children.
-Pernicious anemia is caused by inadequate absorption of vitamin B12 because the stomach does not produce enough intrinsic factor needed for its absorption (745)
-Sickle cell anemia is caused by an abnormal form of hemoglobin in those with sickle cell disease which reduces the amount of oxygen carried by erythrocytes (749)
-thalassemias are a group of inherited disorders caused by an imbalance in the production of one of the four amino acid chains of hemoglobin (751)
-aplastic anemia is caused by aplasia of the bone marrow by toxic agents or can be idiopathic (Thomas, 1970, A76).
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