The Circulatory System
A major source of body energy, transported to the cells by the plasma, is glucose.
Diseases of the Blood
Anemia is a deficiency of hemoglobin in the blood. It can be caused by blood loss, abnormal destruction of the red cells, and inadequate red cell formation by the bone marrow.
Anemia caused by acute or chronic blood loss, or abnormal bleeding, results from the inability of the bone marrow to make new cells as fast as they are needed. In acute or massive bleeding, the red blood cells and their hemoglobin are normal but are not abundant. Chronic slow bleeding leads to a deficiency in iron stores needed for hemoglobin. This results in smaller red blood cells that are paler than normal.
Abnormal destruction of red cells (the hemolytic anemias) leads to a shorter than normal red cell survival. For example, in the hereditary disease Sickle-cell Anemia the hemoglobin is built erroneously. Such cells are more fragile and break more readily in circulation.
Anemias caused by bone-marrow failure include aplastic anemia, in which the bone marrow lacks adequate numbers of some or all types of blood cells. Another anemia caused by failure of production of red cells is pernicious anemia. In this disease, the person's stomach fails to produce "intrinsic factor," which is necessary for the normal absorption of vitamin B-12 from the intestines. Because vitamin B-12 is essential for normal bone marrow function, red cells are not formed normally. Sublingual vitamin B-12 supplements are available, from which the vitamin is absorbed through the blood vessels under the tongue, thus avoiding the potential problems associated with intestinal absorption.
Pernicious anemia results when the person's stomach fails to produce intrinsic factor, which is necessary for the normal absorption of vitamin ________.
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