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X-Nuclei MRI and Energy Metabolism
Published in Guillaume Madelin, X-Nuclei Magnetic Resonance Imaging, 2022
Fermentation process: Producing ATP without oxygen. In absence of oxygen (anaerobic conditions), when, for example, muscle exercise metabolizes glucose too fast and all oxygen available is rapidly metabolized in mitochondria, or in ischemia where blood supply is restricted and causes a shortage of oxygen (and ETC cannot proceed), respiring cells can use lactic acid fermentation as an emergency backup to produce ATP with much lower efficiency (2 ATP per glucose), but also in a much quicker way than the usual cellular respiration pathway. Indeed, when there is no final electron-acceptor oxygen available in the ETC, NADH cannot donates its electrons and oxidative phosphorylation cannot process to synthesize high amounts of ATP (29–38 ATP per glucose). Fermentation is a metabolic pathway that can regenerate NAD+ by oxidizing the excess of NADH so it can be reused in glycolysis, using pyruvate itself as an electron acceptor. Fermentation can be summarized into a 2-step cycle occurring in the cytoplasm: Glycolysis: Glucose is metabolized into 2 pyruvates during glycolysis (as in the first phase of cellular respiration), during which 2 NAD+ are reduced to NADH, and 2 ATP are synthesized from substrate-level phosphorylation. Pyruvate then stays in the cytoplasm and does not enter the mitochondrion for the link reaction.Lactic acid fermentation: Since in anaerobic conditions the ETC cannot proceed to oxidize NADH into NAD+, NADH will use pyruvate (or a molecule derived from pyruvate) as an electron receptor, which is then reduced to regenerate NAD+. Pyruvate is first converted into lactic acid, and then into its conjugate base lactate, in a reversible reaction catalyzed by the lactate dehydrogenase enzyme. NAD+ can reenter the glycolysis pathway in the cytoplasm to synthesize more ATP from glucose. Lactate can be either converted back to pyruvate by the same enzyme, or excreted as waste product by the cell. The role of lactate in the body is still not well understood [14–17].
Lactate detection by colorimetric measurement in real human sweat by microfluidic-based biosensor on flexible substrate
Published in The Journal of The Textile Institute, 2019
Arife Kuşbaz, İkilem Göcek, Gülçin Baysal, Fatma Neşe Kök, Levent Trabzon, Hüseyin Kizil, Burçak Karagüzel Kayaoğlu
Coyle et al. (2014) and Yang et al. (2017) reported that human sweat may be used to check the fitness and optimize performance in sports and exercise since it contains metabolic information of the body and can be collected noninvasively. Moreover its properties may vary between individuals and be affected by sweat rate and type of exercise. As the sweating rate increases, the sweat content changes due to the increase in water loss. In the state of high physical activity, in the case of people in bad physical state, the cells accelerate lactic acid fermentation used in anaerobic conditions in order to generate energy since the circulatory system cannot transport sufficient oxygen to tissues. Lactic acid fermentation leads to lactate accumulation, at the same time prevents further physical activity. Therefore, the endurance of an athlete can be determined by the maximum lactate level and lactate elimination rate.