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8.5Summary

  • Food is decomposed in the digestive organs starting with the mouth and is hydrolyzed with digestive juices secreted from the mouth, stomach, pancreas, and small intestine.
  • Sugars and proteins are degraded into glucose and amino acids or short peptides, respectively. They are then absorbed from the epithelial cells of the small intestine and transported to the veins via the portal vein and liver.
  • Innumerable anaerobic enteric bacteria coexist symbiotically in the intestinal canals. A stable bacterial flora is necessary for good health.
  • The digestive tracts form the interface between the body and the external environment. They have sophisticated biodefense systems that do not react to self tissues and beneficial components while eliminating harmful bacteria, as well as their regulatory systems.
  • Foodstuff such as sugars and lipids are degraded by chemical reactions catalyzed by enzymes. They produce ATP, a high energy molecule that can be used for biological tasks, thereby providing energy for human activities.
  • In addition to degradation, humans synthesize molecules they need. This whole process is referred to as metabolism and constitutes a complex network. Hormones regulate metabolism such that it does not greatly deviate from the stationary state.
  • However, recent changes in lifestyle have brought about disturbance in metabolism, such as "metabolic syndrome." It is important to review our lifestyle, taking into consideration the basics of metabolism.

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