但氧气不足的时候，身体会暂时将丙酮酸转换成为乳酸，使得葡萄糖能够继续分解，以便产生能量。
When the body has plenty of oxygen, pyruvate is shuttled to anaerobic pathway to be further broken down for more energy.
在这种情况下，只有在几次呼吸不足出现，导致血液中二氧化碳大量增加和氧气减少后，呼吸的力度才得到调整。
Only after several inadequate breaths under such conditions, resulting in the considerable elevation of carbon dioxide and reduction of oxygen in the blood, is breathing effort adjusted.
很长一段时间，人们都相信打哈欠是因为血液里二氧化碳太多而氧气不足，大脑茎干觉察到这点于是触动了打哈欠的神经。
It was long believed you yawned when there was too much carbon dioxide and not enough oxygen in your blood. A part of your brain called the brain stem detected this and triggered the yawn reflex.
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