Methemoglobinemia pathophysiology: Difference between revisions
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==Overview== | ==Overview== | ||
Hemoglobin is a protein found in all red blood cells (RBCs), that carries oxygen with the help of iron. In order for this iron to be able to combine with oxygen and turn into oxyhemoglobin, it needs to be in its reduced or ferrous state (Fe2+). Hemoglobin can only accept, transport and release oxygen to the tissues when the iron is in ferrous state. | |||
Methemoglobin (MetHb) refers to the state of Hemoglobin (Hb) in which the iron atom is oxidized or in ferric state (Fe3+). In this state the iron is incapable of creating a bond with the oxygen, thus it neither can bind, nor deliver oxygen to the tissues. The formation of methemoglobin is the result of a normal physiologic process of losing an electron from the iron atom, after releasing the oxygen to the tissues, and we can detect methemoglobin in the blood of healthy people, but the normal levels should always be less than 1%. These levels are maintained by several enzyme systems that work to reduce the iron to its ferrous state (Fe2+). | |||
The two most important enzymes are the diaphorase I (requiring nicotinamide adenine dinucleotide -NADH as a co-factor) and diaphorase II (requiring nicotinamide adenine dinucleotide phosphate – NADPH as a co-factor). | |||
Almost 99% of the methemoglobin normally produced is removed by the diaphorase I pathway. Here electrons from NADH are transferred to methemoglobin, with the help of cytochrome b5 reductase, to reduce it to hemoglobin. | |||
In patients with deficiency of NADH-cytochrome b5 reductase, which is an autosomal recessive disorder, the diaphorase II pathway becomes the main enzyme system that removes methemoglobin by reducing it to hemoglobin with the help of glucose-6-phosphate dehydrogenase (G6PD). | |||
There are two major causes that can lead to the formation of methemoglobin - acquired and congenital. | |||
==Pathophysiology== | ==Pathophysiology== | ||
Revision as of 10:34, 29 April 2018
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Hemoglobin is a protein found in all red blood cells (RBCs), that carries oxygen with the help of iron. In order for this iron to be able to combine with oxygen and turn into oxyhemoglobin, it needs to be in its reduced or ferrous state (Fe2+). Hemoglobin can only accept, transport and release oxygen to the tissues when the iron is in ferrous state.
Methemoglobin (MetHb) refers to the state of Hemoglobin (Hb) in which the iron atom is oxidized or in ferric state (Fe3+). In this state the iron is incapable of creating a bond with the oxygen, thus it neither can bind, nor deliver oxygen to the tissues. The formation of methemoglobin is the result of a normal physiologic process of losing an electron from the iron atom, after releasing the oxygen to the tissues, and we can detect methemoglobin in the blood of healthy people, but the normal levels should always be less than 1%. These levels are maintained by several enzyme systems that work to reduce the iron to its ferrous state (Fe2+). The two most important enzymes are the diaphorase I (requiring nicotinamide adenine dinucleotide -NADH as a co-factor) and diaphorase II (requiring nicotinamide adenine dinucleotide phosphate – NADPH as a co-factor).
Almost 99% of the methemoglobin normally produced is removed by the diaphorase I pathway. Here electrons from NADH are transferred to methemoglobin, with the help of cytochrome b5 reductase, to reduce it to hemoglobin.
In patients with deficiency of NADH-cytochrome b5 reductase, which is an autosomal recessive disorder, the diaphorase II pathway becomes the main enzyme system that removes methemoglobin by reducing it to hemoglobin with the help of glucose-6-phosphate dehydrogenase (G6PD).
There are two major causes that can lead to the formation of methemoglobin - acquired and congenital.