Thrombocytopenia means the presence of very low numbers of platelets in the circulating blood. People with thrombocytopenia have a tendency to bleed, as do hemophiliacs, except that the bleeding is usually from many small venules or capillaries, rather than from larger vessels as in hemophilia. As a result, small punctate hemorrhages occur throughout all the body tissues. The skin of such a person displays many small, purplish blotches, giving the disease the name throm-bocytopenic purpura. As stated earlier, platelets are especially important for repair of minute breaks in capillaries and other small vessels.
Ordinarily, bleeding will not occur until the number of platelets in the blood falls below 50,000/|ml, rather than the normal 150,000 to 300,000. Levels as low as 10,000/|ml are frequently lethal.
Even without making specific platelet counts in the blood, sometimes one can suspect the existence of thrombocytopenia if the person's blood fails to retract, because, as pointed out earlier, clot retraction is normally dependent on release of multiple coagulation factors from the large numbers of platelets entrapped in the fibrin mesh of the clot.
Most people with thrombocytopenia have the disease known as idiopathic thrombocytopenia, which means thrombocytopenia of unknown cause. In most of these people, it has been discovered that for unknown reasons, specific antibodies have formed and react against the platelets themselves to destroy them. Relief from bleeding for 1 to 4 days can often be effected in a patient with thrombocytopenia by giving fresh whole blood transfusions that contain large numbers of platelets. Also, splenectomy is often helpful, sometimes effecting almost complete cure because the spleen normally removes large numbers of platelets from the blood.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.