Anemia and Polycythemia Lecture Notes PDF

Anemias and polycythemia ILOs By the end of this lecture, students will be able to 1. Classify types of anemia in relation to their etiology 2. Relate the pathophysiology of anemia to red blood cell morphologic abnormalities 3. Differentiate between primary and secondary polycythemia Anemia is the s...

Anemias and polycythemia ILOs By the end of this lecture, students will be able to 1. Classify types of anemia in relation to their etiology 2. Relate the pathophysiology of anemia to red blood cell morphologic abnormalities 3. Differentiate between primary and secondary polycythemia Anemia is the state of low hemoglobin or red blood cell count in blood, resulting in reduced oxygen binding capacity. It may be the result of i) blood loss, ii) insufficient erythropoiesis (reduced red blood cell production), or iii) hemolysis (red blood cell destruction). Blood Loss Anemia. After rapid hemorrhage, the body replaces the fluid portion of the plasma in 1 to 3 days, but this leaves a low concentration of red blood cells. If a second hemorrhage does not occur, the red blood cell concentration usually returns to normal within 3 to 6 weeks. In chronic blood loss, a person frequently cannot absorb enough iron from the intestines to form hemoglobin as rapidly as it is lost. Red cells are then produced that are much smaller than normal and have too little hemoglobin inside them, giving rise to iron deficiency anemia. Insufficient erythropoiesis anemias Aplastic Anemia. Bone marrow aplasia means lack of functioning bone marrow. For instance, a person exposed to gamma ray radiation from a nuclear bomb blast can sustain complete destruction of bone marrow, followed in a few weeks by lethal anemia. Likewise, excessive x-ray treatment, certain industrial chemicals, and even drugs to which the person might be sensitive can cause the same effect. Iron Deficiency anemia Most of the iron in the diet is in the ferric (Fe3+) form, but it is absorbed in the ferrous (Fe2+) form Gastric secretions dissolve the iron and permit it to form soluble complexes with ascorbic acid that aids its reduction to the Fe2+ form. Therefore, iron deficiency anemia is a frequent complication of partial gastrectomy. Also it occurs due to chronic blood loss. Megaloblastic Anemia. Based on the earlier discussions of vitamin B12, folic acid, and intrinsic factor from the stomach mucosa, one can readily understand that loss of any one of these can lead to slow reproduction of erythroblasts in the bone marrow. As a result, the red cells grow too large, with odd shapes, and are called megaloblasts. Thus, atrophy of the stomach mucosa, as occurs in pernicious anemia, or loss of Page 1 of 5 the entire stomach after surgical total gastrectomy can lead to megaloblastic anemia. Also, patients who have intestinal sprue, in which folic acid, vitamin B12, and other vitamin B compounds are poorly absorbed, often develop megaloblastic anemia. Because in these states the erythroblasts cannot proliferate rapidly enough to form normal numbers of red blood cells, those red cells that are formed are mostly oversized, have bizarre shapes, and have fragile membranes. These cells rupture easily, leaving the person in dire need of an adequate number of red cells. Hemolytic Anemia. Different abnormalities of the red blood cells, the cells fragile, so that they rupture easily as they go through the capillaries, especially through the spleen. Even though the number of red blood cells formed may be normal, or even much greater than normal in some hemolytic diseases, the life span of the fragile red cell is so short that the cells are destroyed faster than they can be formed, and serious anemia results. This type of anemia is either hereditary or acquired 1- Hereditary Hemolytic Anemia. `Hereditary spherocytosis: The red cells are very small and spherical rather than being biconcave discs. These cells cannot withstand compression forces because they do not have the normal loose, baglike cell membrane structure of the biconcave discs. On passing through the splenic pulp and some other tight vascular beds, they are easily ruptured by even slight compression. Sickle cell anemia: The cells have an abnormal type of hemoglobin called hemoglobin S, containing faulty beta chains in the hemoglobin molecule, when this hemoglobin is exposed to low concentrations of oxygen, it precipitates into long crystals inside the red blood cell. These crystals elongate the cell and give it the appearance of a sickle rather than a biconcave disc. The precipitated hemoglobin also damages the cell membrane, so that the cells become highly fragile, leading to serious anemia. Such patients frequently experience a vicious circle of events called a sickle cell disease “crisis,” in which low oxygen tension in the tissues causes sickling, which leads to ruptured red cells, which causes a further decrease in oxygen tension and still more sickling and red cell destruction. Once the process starts, it progresses rapidly, eventuating in a serious decrease in red blood cells within a few hours and, often, death. 2- Hereditary Hemolytic Anemia Hemolytic anemia of the newborn “Erythroblastosis fetalis” Rh-positive red blood cells in the fetus are attacked by antibodies from an Rh-negative mother. These antibodies make the Rh-positive cells fragile, leading to rapid hemolysis and causing the child to be born with serious anemia. The extremely rapid formation of new red cells to make up for the destroyed cells causes a large number of early blast forms of red cells to be released from the bone marrow into the blood. Page 2 of 5 Mismatched blood transfusion Reaction to some drugs Infections ex. Malaria NB. There are other types of anemia ex Thalassemia a hemoglobin disorder may result in mild or severe anemia, secondary anemia as occurs with chronic renal failure ,hypothyroidism. Morphologic classification of anemias According to red cell volume (mean corpuscular volume; MCV) and mean cell haemoglobin (MCH), (Fig 1 ) anemia is classified into: 1- Normocytic normochromic anemia Occur in acute haemolytic anemia and in acute blood loss. The red cells are of normal size (normocytic) and of normal haemoglobin content (normochromic). 2- Microcytic hypochromic anemia They are most often due to iron deficiency in the diet or chronic blood loss with loss of large amounts of iron over a long period. The red blood cells are small in size (microcytic) and the haemoglobin content of each cell is less than normal (hypochromic) 3- Macrocytic normochromic anemia These are associated with megaloblastic erythropoiesis due to deficiency of vitamin B12 and folic acid. The red blood cells are larger in size (macrocytic) and of normal haemoglobin content (normochromic). Page 3 of 5 Polycythemia An increase of red cell count and or an increase of blood haemoglobin level 2 grams above the normal value. Primary polycythemia ( polycythemia Vera). It is a pathological condition, in which the red blood cell count may be 7 to 8 million/mm3 and the hematocrit may be 60 to 70 per cent instead of the normal 40 to 45 per cent. Polycythemia vera is caused by a genetic aberration in the hemocytoblastic cells that produce the blood cells. The blast cells no longer stop producing red cells when too many cells are already present. Secondary Polycythemia. Whenever the tissues become hypoxic because of too little oxygen in the breathed air, such as at high altitudes, or because of failure of oxygen delivery to the tissues, such as in cardiac failure, the blood-forming organs automatically produce large quantities of extra red blood cells. This condition is called secondary polycythemia, and the red cell count commonly rises to 6 to 7 million/mm3, about 30 per cent above normal. A common type of secondary polycythemia, called physiologic polycythemia, occurs in natives who live at altitudes of 14,000 to 17,000 feet, where the atmospheric oxygen is very low. The blood count Page 4 of 5 is generally 6 to 7 million/mm3; this allows these people to perform reasonably high levels of continuous work even in a rarefied atmosphere. Page 5 of 5