本帖最后由 polar_bear 于 2015-1-1 19:49 编辑 * `+ N: m( I, L+ d# E
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好吧,我先说。我看看中医又看看西医,终于悟出了下面的道理: 西医:Transport of Carbon Dioxidein the Blood Carbondioxide molecules are transported in the blood from body tissues to the lungsby one of three methods: (1) dissolution directly into the blood, (2) bindingto hemoglobin, or (3) carried as a bicarbonate ion. Several properties ofcarbon dioxide in the blood affect its transport. First,carbon dioxide is more soluble in blood than is oxygen. About 5 to 7 percent ofall carbon dioxide is dissolved in the plasma. Second,carbon dioxide can bind to plasma proteins or can enter red blood cells andbind to hemoglobin. This form transports about 10 percent of the carbondioxide. When carbon dioxide binds to hemoglobin, a molecule calledcarbaminohemoglobin is formed. Binding of carbon dioxide to hemoglobin isreversible. Therefore, when it reaches the lungs, the carbon dioxide can freelydissociate from the hemoglobin and be expelled from the body. Third,the majority of carbon dioxide molecules (85 percent) are carried as part ofthe bicarbonate buffer system. In this system, carbon dioxide diffuses into thered blood cells. Carbonic anhydrase (CA) within the red blood cells quicklyconverts the carbon dioxide into carbonic acid (H2CO3). Carbonic acid is anunstable, intermediate molecule that immediately dissociates into bicarbonateions (HCO3−) andhydrogen (H+) ions. Since carbon dioxide is quickly converted into bicarbonateions, this reaction allows for the continued uptake of carbon dioxide into theblood, down its concentration gradient. It also results in the production of H+ions. If too much H+ is produced, it can alter blood pH. However, hemoglobinbinds to the free H+ ions, limiting shifts in pH. The newly-synthesizedbicarbonate ion is transported out of the red blood cell into the liquidcomponent of the blood in exchange for a chloride ion (Cl-); this is called thechloride shift. When the blood reaches the lungs, the bicarbonate ion istransported back into the red blood cell in exchange for the chloride ion. TheH+ ion dissociates from the hemoglobin and binds to the bicarbonate ion. Thisproduces the carbonic acid intermediate, which is converted back into carbondioxide through the enzymatic action of CA. The carbon dioxide produced isexpelled through the lungs during exhalation. Thebenefit of the bicarbonate buffer system is that carbon dioxide is "soakedup" into the blood with little change to the pH of the system. This isimportant because it takes only a small change in the overall pH of the bodyfor severe injury or death to result. The presence of this bicarbonate buffersystem also allows for people to travel and live at high altitudes. When thepartial pressure of oxygen and carbon dioxide change at high altitudes, thebicarbonate buffer system adjusts to regulate carbon dioxide while maintainingthe correct pH in the body. Source:Boundless. “Transport of Carbon Dioxide in the Blood.” Boundless Biology.Boundless, 14 Nov. 2014. Retrieved 02 Jan. 2015 fromhttps://www.boundless.com/biology/textbooks/boundless-biology-textbook/the-respiratory-system-39/transport-of-gases-in-human-bodily-fluids-222/transport-of-carbon-dioxide-in-the-blood-842-12087/ Farts are caused by trapped air, which can come from many sources. Some ofit is air that we have swallowed while chewing or drinking. Some air is causedby gas seeping into our intestines from our blood, and some gas is produced bychemical reactions in our intestines or bacteria living in our guts. A typicalfart is composed of about 59 percent nitrogen, 21 percent hydrogen, 9 percentcarbon dioxide, 7 percent methane and 4 percent oxygen. Only about one percentof a fart contains hydrogen sulfide gas and mercaptans, which contain sulfur,and the sulfur is what makes farts stink. 中医:肺和大肠相表里,如果因为饮冷伤肺,那么更多的CO2会从大肠里出去的,这就解释了为什么大多数屁不臭和硬憋时有气上冲的感觉了。 个人理解,欢迎讨论 |