Anemia.

Anemia. I INTRODUCTION Anemia, medical condition caused by an abnormally low number of red blood cells. Red blood cells, also called erythrocytes, contain hemoglobin, a red, iron-rich protein that carries oxygen in the blood to the body's tissues. People with anemia develop symptoms caused by the poor delivery of oxygen to their body tissues. These symptoms include pale skin, shortness of breath, rapid heartbeat, low vitality, dizziness, and, if left untreated, stroke or heart failure. II CAUSES There are three primary causes of anemia: (1) reduced production of red blood cells; (2) excessive destruction of red blood cells; and (3) extensive bleeding. A Reduced Production of Red Blood Cells Red blood cell production becomes impaired if the body has inadequate amounts of certain nutrients, including iron, vitamin B12, and folic acid, as well as the hormone erythropoietin, which is produced by the kidneys. Chronic illnesses, such as cancer, kidney disease, diabetes mellitus, and inflammatory bowel disease, may also lead to decreased red blood cell production. B Destruction of Red Blood Cells Red blood cells normally live for about 120 days before the immune system removes them from the body. The body compensates by producing new red blood cells. But if the destruction of red blood cells exceeds the body's ability to produce new red blood cells, anemia results. Abnormal destruction of red blood cells may be caused by an enlarged spleen, an organ that removes worn red blood cells from the body. The larger the spleen grows, the more red blood cells it traps and destroys. In some cases red blood cells are destroyed by a malfunction of the immune system in which antibodies attach to red blood cells, marking them for destruction. Red blood cells may also be destroyed by some genetic conditions, such as thalassemia, that cause defects in the structure or function of red blood cells. C Bleeding Excessive bleeding can cause dangerously low blood pressure as well as insufficient oxygen delivery to body tissues. Large amounts of blood loss may occur suddenly due to injury or surgery. In some cases, excessive bleeding may occur over time, such as from bleeding ulcers or tumors of the intestinal tract. III TYPES OF ANEMIA There are more than 100 types of anemia. The most common type is iron-deficiency anemia. When the body's need for iron increases--such as during periods of rapid growth in childhood, during pregnancy, or when there is chronic bleeding--an iron deficiency may develop. Low iron levels impair the body's ability to produce hemoglobin, a primary component of red blood cells. Pernicious anemia, a chronic ailment that mostly affects people over 40, is a result of vitamin B12 deficiency. This vitamin is normally found in meats and vegetables and is essential for the maturation of red blood cells. People with pernicious anemia are unable to produce intrinsic factor, a substance that allows the small intestine to absorb vitamin B12. This inability may be caused by a genetic disorder, Crohn's disease (an immune system disorder that causes chronic inflammation of the digestive tract), or surgery that removes the part of the stomach that normally produces intrinsic factor. Aplastic anemia occurs when bone marrow, the tissue that produces new red blood cells, becomes diseased or injured. Bone marrow damage may result from a viral infection, cancer, radiation, or exposure to toxic chemicals, including arsenic, benzene, and some antibiotics and cancer medications. Sickle-cell anemia is an inherited disorder that affects mostly people of African ancestry. People with sickle-cell anemia have an abnormal form of hemoglobin that distorts red blood cells. These distorted cells are called sickled cells because of their resemblance to the sickle, a type of crescent-shaped cutting blade used in agriculture. The sickled shape makes it difficult for these cells to pass through tiny blood vessels, preventing oxygen in the blood from reaching organs and tissues. IV TREATMENT Physicians treat anemia associated with a serious disease by treating the underlying disorder. In some cases, when symptoms persist or worsen, additional medications that boost red blood cells may be necessary to avoid life-threatening conditions and improve quality of life. For instance, doctors prescribe iron pills to treat irondeficiency anemia and injections of vitamin B12 to treat pernicious anemia. Synthetically manufactured erythropoietin stimulates the production and growth of red blood cells in people with kidney disease or cancer. Blood transfusions may be used in cases of massive blood loss. Removal of the spleen may prevent blood cells from being removed from the circulation of the blood or destroyed too rapidly. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.