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Lactose and lactic acid crystals. Lactose is a disaccharide consisting of two subunits, a galactose and a glucose linked together. In young mammals, an enzyme called lactase is secreted by the intestinal villi, and this enzyme cleaves the molecule into its two subunits for absorption. Normally, as the young grow up, production of lactase gradually ceases, and they are then unable to metabolize lactose. This is perhaps an evolutionary mechanism to enforce weaning of the young. Lactose is the sugar making up around 2-8% of the solids in milk. Lactic acid is a chemical compound that plays a role in several biochemical processes. It is the acid that gives old milk its sour taste, and it accumulates in skeletal muscles during extensive anaerobic exercise, causing temporary muscle pain. Lactic acid is quickly removed from muscles when they resume aerobic metabolism. Lactic acid fermentation occurs in red blood cells since they don't have mitochondria, and in skeletal muscle during intense exertion when sufficient amounts of oxygen cannot be supplied fast enough. Thus lactate is released into the bloodstream. The liver takes up about 60% of the lactate and re-oxidizes it to pyruvate, which is then reconverted to glucose in a process known as gluconeogenesis. The glucose enters the bloodstream and can be used by the tissues. Lactic acid fermentation is also performed by lactic acid bacteria which are responsible for the sour taste of old milk and which are used in the production of dairy products such as cheese. Lactic acid bacteria also operates in the mouth, and the resulting lactic acid is responsible for the tooth decay known as caries. Lactic acid is also the result of malolactic fermentation, a process used in winemaking to convert sharp-tasting malic acid into the gentler lactic acid.
| 860515-24.tif 12.01.04 crystal crystals dental disease galactose glucose gluconeogenesis lactose lactase lactic acid lactic acid bacteria lactic acid fermentation malic acid malolactic fermentation mouth flora oral bacteria oral cavity pyruvate sugar sour taste skeletal muscle tooth decay LM |
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