Module 2 Week 3.docx - MODULE 2 Functionality Sequence of...

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MODULE 2: Functionality & Sequence of the Digestive System Nutrition world divides the nutrients into two major categories, the macronutrients and the micronutrients. We're going to begin our discussion with the macronutrients. These macronutrients are carbohydrates, the proteins, and the fats. What we will see is the number of mechanisms that the body uses in order to extract these elements from the food into our bodies. We're going to take up carbohydrates first, primarily because that's the most of the calories that we eat are in the form of carbohydrates. About 50 to 60% of the calories that we eat at each meal will come from the carbohydrates. The only reason we eat carbohydrates is for the energy. That energy is stacked in terms of carbohydrates, stored in various forms. And the process of digestion is the slowly unfolding of energy from these foods to a form that the body uses. The only form that the body can use is in the form of ATPs. Now, carbohydrate comes in three different forms. There are the monosaccharides; these are the easy sugars. The disaccharides, which are combinations of monosaccharides. And then polysaccharides are a whole series of these carbohydrates that are all bound together. Each of these disaccharides and monosaccharides and polysaccharides requires its own mechanism for absorption and in succeeding videos we'll take on each of this as they arise. Week 3 Absorbing Carbs: Monosaccharides There are three kinds of monosaccharides that exist in nature, the most prevalent being glucose. Glucose that exists in nature is the same glucose that exists inside our bodies. It's prevalent. The important thing to note is that glucose contains six carbons. I mention this because the energy that is stored in glucose is stored in these carbon bonds, and we'll see later how the body can extract this energy from these carbon bonds. A second type of monosaccharide is galactose. Galactose is mother's milk. It is the sugar that is in milk that makes it taste sweet. The reason why all infants love to drink mother's milk is because of its sweetness. It is rarely found outside of milk in nature. The third and the most controversial of the monosaccharides is fructose. Fructose is called fruit sugar because it is the major monosaccharide that is in most sweet fruits. It is different than the other two monosaccharides in that it contains only five carbons, rather than the six of glucose and galactose. The monosaccharides are quite easy to absorb. Once they get into the intestinal lumen, they are readily picked up in these intestinal cells, taken right to the blood supply. And from there, they go right to the liver. Absorbing Carbs: Disaccharides Disaccharides have a bigger problem than monosaccharides. Disaccharides cannot be directly absorbed into the intestine, but they have to be broken down into their monosaccharide constituents. So, sucrose which is a disaccharide, consists of two monosaccharides, glucose and fructose. Maltose consists of two glucose molecules that are bound together. And finally, we have lactose, which
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  • Fall '05
  • LEVITSKY
  • Glucose

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