Friday, May 11, 2012

Hypoxia is a decrease of oxygen supply to body organs and tissues. There are several causes of hypoxia, but they can be classed in four general categories: 1) hypoxic hypoxia (also termed hypoxemia), in which the arterial PO2 is reduced; 2) anemic or carbon monoxide hypoxia, in which the arterial PO2 is normal but the total oxygen content of the blood is reduced because of inadequate numbers of erythrocytes, deficient or abnormal hemoglobin, or competition for the hemoglobin molecule by carbon monoxide; 3) ischemic hypoxia (also called hypoperfusion hypoxia), in which blood flow to the tissues is too low; and 4) histotoxic hypoxia, in which the quantity of oxygen reaching the tissues is normal but the cell is unable to utilize the oxygen because a toxic agent—cyanide, for example—has interfered with the cell’s metabolic machinery. Exposure to the reduced PO2 of high altitude also causes hypoxic hypoxia but is, of course, not a "disease."