Anemia is a deficiency of hemoglobin in the blood, generally caused by blood loss; abnormal destruction of the red cells, as in Sickle-cell disease; or inadequate red cells formation by the bone marrow, as in a plasmatic anemia and pernicious anemia. Anemia also occurs as a result of methermoglobinemia, a disorder in which methemoglobin, a nonfunctional form of hemoglobin, is present in the red cells.
In some persons, the concentration of red cells and of hemoglobin in the blood may be abnormally increased, rather than decreased, resulting in polycythemia. This is usually caused by an increased production of red cells, but in some persons it may be caused by a decreased volume of plasma.
Deficiency of circulating granulocytes with poor resistance to infection, may occur in many diseases. One common cause is the use of X rays and toxic drugs to treat many malignant diseases.
A great increase in abnormal leukecytes may occur for unknown reasons, resulting in the diseases known as the leukemias. These range from the chronic lymphocytic leukemia, in which a person may live form many years, to devastating acute leukemia, often causing death within month.
The number of platelets can severely decrease, with danger of bleeding. Perhaps the most common cause of platelet deficiency, or thrombocytopenia, is an autoimmune disease related to autoimmune hemolytic anemia. The difference is that, in these cases, the body produces antibodies that attack only the platelets.
Deficiencies of one or more of the plasma coagulation factors may also cause abnormal bleeding. The existence of many of the clothing factors was recognized only when persons were found who lacked such a factor. The best known such bleeding disorder is Hemophilia.
Abnormal clotting in the blood vessels, known as thromboembolic disease, may be caused by an excess of one or more of the plasma clothing factors, or at times to a deficiency of one of the fibrinolytic factors. This group of disorders is one of the most common causes of death in middle aged and elderly persons.
Thursday, May 15, 2008