Chapter 51 Digestion

Chapter 51 Digestion - Animal nutrition Nutrient...

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Nutrient requirements Structure and function of the human GI tract Accessory digestive organs Regulation of digestion and nutrient delivery Animal nutrition Animals are heterotrophs, deriving their energy and structural building blocks from food, therefore ultimately from autotrophs, who rely on photosynthesis. Basal metabolic rate of adult humans is ~1500 kcal/day. calorie (1 gm water, 1 deg C) kcal (Calorie).
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Utilization of stored energy Most animals do not eat continuously, so they store fuel molecules that can be released as needed between meals. Carbohydrates are stored in liver and muscle cells as glycogen. The total glycogen store (4.2 kcal/gm) is usually not more than the equivalent of a day’s energy requirements. The most important form of stored energy in animals is fat. Fat is the most energetically dense form of storage (9.5 kcal/gm), and it is stored with little associated water, making it more compact. Protein (4.1 kcal/gm) is not used to store energy, but protein can be metabolized as an energy source of last resort.
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For many animals, food provides essential carbon skeletons they cannot synthesize themselves. Examples include the acetyl group shown below and essential fatty acids like linoleic acid for synthesis of unsaturated fatty acids. Essential carbon skeletons
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Essential amino acids Meat, milk, and eggs (and soybeans) contain all 8. Vegetarians must mix complementary protein sources like rice and beans, corn and beans, bread and peanut butter. Without all 8, the meal fails to support protein synthesis. Kwashiorkor!
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Enzyme partners Cofactors are inorganic ions that bind to enzymes temporarily and can transfer electrons for oxidation/reduction reactions. Coenzymes, small organic molecules, bind like a substrate and change chemically in cycles, adding or removing chemical groups. Prosthetic groups are permanently bound.
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Macronutrients – elements required in large amounts (e.g. 1 gm/day)
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Table 50.1 Mineral Elements Required by Animals (Part 2) Micronutrients – elements required in small amounts (e.g. 10 mg/day)
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Humans require 13 vitamins
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Tubular gut Digestion involves breaking down complex food molecules into monomers that can be absorbed and utilized by cells, employing carbohydrases, proteases, lipases, In most animals, digestion is extracellular, external to the body, occurring in a tubular gut with specialized regions: mouth/teeth to break up food; stomach for storage; midgut (intestine) for digestion and absorption; hindgut (colon) for retrieval of water and ions; anus for expelling solid waste.
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The Human Gastrointestinal Tract To the tubular gut, add accessory organs like the liver, pancreas, and gallbladder.
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Specialized Regions of the GI Tract Mouth – initiates starch digestion (amylase), in many cases there are specialized structures to assist in the breakdown of food e.g. (teeth, mandibles) Esophagus – conducts food from mouth to stomach Stomach – initiates protein digestion, stores food to regulate
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This note was uploaded on 04/19/2011 for the course LS 2 taught by Professor Pires during the Spring '08 term at UCLA.

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Chapter 51 Digestion - Animal nutrition Nutrient...

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