Methane
描述
Methane (CH4), is a gas produced by a group of colonic anaerobes, absorbed from the colon and excreted in expired air. As a result, breath CH4 excretion can be used as an indicator of the in situ activity of the methanogenic flora. All CH4 produced in human beings is a metabolic product of intestinal bacteria, and about 50% of CH4 produced in the gut is absorbed and excreted in expired air. Because there appears to be no catabolism of this gas by other colonic organisms or host cells, breath CH4 measurements provide a rapid, simple means of semi quantitatively assessing the ongoing in situ metabolism of the methanogenic flora. It could seem likely that the intracolonic activity of a variety of bacteria similarly might be assessed quantitatively via analysis of expired air. However, the application of this methodology has been confounded by the rapid catabolism of many volatile bacterial products by other bacteria or human tissue. A striking aspect of the studies of breath CH4 measurements is the enormous individual variations in the excretion of this gas. Virtually all children under 5 years of age and 66% of the adult population do not exhale appreciable quantities of CH4. The remaining 34% of the adult population has appreciable breath methane concentrations of up to 80 ppm (mean, 15.2 ppm; median, 11.8 ppm). On this basis the population can be divided into CH4 producers or nonproducers, although a more accurate term would be to define subjects as being low or high CH4 producers. The primary methanogen present in the human colon, Methanobrevibacter smithii, produces methane via a reaction that relies entirely on H2 produced by other organisms to reduce CO2 to CH4. Thus, breath CH4 concentrations might be expected to mirror breath H2 concentrations; however, the high levels of CH4 observed in the fasting state may result from H2 derived from endogenous rather than dietary substrates. A diverse assortment of conditions has been associated with a high prevalence of methane producers including diverticulosis, cystic fibrosis, high fasting serum cholesterol levels, encopresis in children, and aorto-iliac vascular disease, whereas obesity (measured as skin-fold thickness) was related inversely to methane production. The challenge that remains is to determine to what extent methanogens actively influence body physiology vs. simply serve as passive indicators of colonic function. (A11043)
类别
"Industrial/Workplace Toxin", "Food Toxin", "Natural Toxin"
同义词
"Biogas", "Carbane", "CH4", "Marsh gas", "Methyl hydride", "Tetrahydridocarbon"
InChI 标识符
InChI=1S/CH4/h1H4
键
InChIKey=VNWKTOKETHGBQD-UHFFFAOYSA-N
类型
Saturated hydrocarbons
取代基
"Acyclic alkane", "Aliphatic acyclic compound", "Alkane"
分子框架
Aliphatic acyclic compounds
外部描述符
"a simple group", "alkane", "mononuclear parent hydride", "one-carbon compound"
地位
Detected and Not Quantified
蜂窝位置
"Cytoplasm", "Extracellular"
组织位置
"Adipose Tissue", "Fibroblasts", "Intestine", "Kidney", "Liver", "Muscle", "Platelet"
熔点/沸点/溶解度
-182.4°C//0.022 mg/mL at 25°C
毒性机制
Methane is an asphyxiant and displaces oxygen in enclosed spaces. At high enough concentrations, oxygen depletion may cause asphyxiation. Low concentrations of surrounding oxygen results in deficient oxygen to the organs, compounded by increased oxygen exhalation during respiration. This results in generalized hypoxia and possibly death. (L171, A120)
代谢
Methane is biologically inactive. (L172)
毒性值
LC50: 326 gm/m3 over 2 hours (Inhalation, Mouse) (L173)
致癌性
No indication of carcinogenicity to humans (not listed by IARC).
用途/来源
Methane is the major component of natural gas, which is found in geological deposits known as natural gas fields and used as vehicle fuel in its compressed form. Methane may be burned to produce electricity and is often piped into homes for domestic heating and cooking purposes. Methane is also used in industrial processes to produce chemicals such as hydrogen, methanol, acetic acid, and acetic anhydride. (L171)
健康影响
Methane is an asphyxiant and displaces oxygen in enclosed spaces. At high enough concentrations, oxygen depletion may cause asphyxiation, resulting in generalized hypoxia and possibly death. (L171, L172)
症状
Symptoms of methane asphyxiation include nausea, vomiting, difficulty breathing, irregular heartbeat, headache, drowsiness, fatigue, dizziness, disorientation, mood swings, tingling sensation, loss of coordination,
suffocation, convulsions, unconsciousness, coma, and possibly death. (L173)
治疗
Asphyxiation should be treated by moving the affected person to an uncontaminated area, then giving artificial respiration and administering oxygen, if necessary. (L173)
维基百科链接
http://en.wikipedia.org/wiki/Methane
创建于
2009-03-06 18:58:01 UTC
更新于
2014-12-24 20:21:01 UTC