True Blue BloodsEvery single year that I taught freshman biology, I spent a fair amount of time addr

True Blue BloodsEvery single year that I taught freshman biology, I spent a fair amount of time addressing misconceptions firmly held by my students. One misconception that they clung to was that blood could be blue. They would illustrate this notion by pointing out the veins that could be seen beneath their skin. I repeated many times that “human blood is not blue” (there are animals with copper-based hemocyanin that have blue blood) and would go on to explain why it appears to be blue when you see it through the skin (refracted light).Blood is bright red when oxygenated and a dull brick red when deoxygenated. However, there are some medical conditions in which a person’s skin can appear blue in color (without being a Smurf or a native of the planet Pandora) because of the underlying color of the blood. The best known of these conditions is methemoglobinemia (meth-hee-mo-glo-bin-ee-mia).Found in both inherited and acquired forms, methemoglobinemia occurs when an abnormal amount of methemoglobin (metHB) is produced by the oxidation of hemoglobin. Hemoglobin is an iron-based molecule in blood that carries oxygen to the cells. MetHB, normally found at levels of around 1%, can carry oxygen but is unable to release it for use by the cells. In one of the inherited forms of the syndrome (known as Type 1 or erythrocyte reductase deficiency), the enzyme, cytochrome b5 reductase, which converts metHB into hemoglobin via chemical reduction, is absent. A famous case study of methemoglobinemia involved a family known as “The Blue Fugates of Troublesome Creek”.Martin Fugate, a Frenchman who settled in the Appalachian mountains of Kentucky in the early 1800’s, married a young American woman: Elizabeth Smith. Against all odds, both of them carried a recessive allele for the syndrome (a recessive trait is one which is only expressed when someone inherits alleles from both of their parents). In a rural area confined by the mountainous terrain, their descendants married and intermarried with a small handful of other families for six generations. As the alleles became concentrated within the small gene pool, many of the Fugate descendents had skin that increasingly ranged in color from bright blue to almost purple, especially when cold or angry. Although levels of metHB above 20% can lead to heart abnormalities, seizures, and even death, levels below that can cause the blue appearance of the skin, but no other symptoms. If only one allele is present, the person who is afflicted may exhibit symptoms in infancy, outgrowing it as they mature. Some people having lower percentages of metHB can also exhibit symptoms of respiratory distress due to decreased oxygen levels, but most of the Fugate descendants lived well into their 80’s and 90’s.Finally diagnosed in the family in the 1960’s, methemoglobinemia is rarely seen today. When diagnosed at birth, those with the disorder are commonly treated with the chemical methylene blue or with ascorbic acid, which reduce the iron in metHB molecules, restoring it to its normal state. More severe cases may require alternative treatment with hyperbaric oxygen therapy (breathing pure oxygen in a pressurized chamber) or exchange transfusions.CWImagehttp://emedicine.medscape.com/article/204178-overview**The image most often associated with methemoglobinemia is an old, colorized black and white photo of the Fugate family that does not give a true depiction of the condition. Because I was unable to locate a verifiable image showing how the syndrome manifests itself in a person’s outward appearance, I have used one showing what the difference is in the appearance of the blood itself. However, the doctor who first diagnosed and treated the Fugates, the late Dr. Madison Cawein, described the afflicted members of that family as being “blue as hell”.Sourceshttps://www.nlm.nih.gov/medlineplus/ency/article/000562.htmhttp://emedicine.medscape.com/article/204178-overviewhttp://www.indiana.edu/~oso/lessons/Blues/TheBlues.htmhttp://mayocl.in/1klhZOdhttp://bit.ly/1PgsSu2http://abcn.ws/1o1a5v5 -- source link
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