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Chapter 25

Nutrition, Metabolism,

Temperature Regulation

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Nutrients

• Chemicals used by body

• Classes– Carbohydrates, proteins,

lipids, vitamins, minerals, water

• Food Guide Pyramid– USDA recommends

• Kilocalories– Measure of energy supplied

by food and released through metabolism

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Carbohydrates

• Monosaccharides– Include glucose, fructose, galactose

• Disaccharides– Include sucrose, maltose, lactose

• Polysaccharides (complex)– Include starch, glycogen, cellulose

• Disaccharides and Polysaccharides– Converted to glucose (used for energy or stored

as glycogen or fats)

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Lipids

• Triglycerides (95%): Used for energy to produce ATP or stored in adipose tissue, liver– Saturated fats: Meat fats, whole milk, cheese, eggs– Unsaturated fats: Olive and peanut oil

• Cholesterol: Steroid found in liver, egg yolks but not found in plants

• Phospholipids: Major components of plasma membranes

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Proteins

• Chains of amino acids– Kinds

• Essential (9): Must be obtained in diet

• Nonessential: Body can synthesize

• Functions– Protection (antibodies), regulation (enzymes,

hormones), structure (collagen), muscle contraction (actin, myosin), transportation (hemoglobin, ion channels)

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Recommended Amounts

• Carbohydrates– 60% of daily intake of kilocalories

• Lipids– 30% or less of total daily kilocalories

• Proteins– 10% of total kilocalories per day

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Vitamins

• Function as coenzymes or parts of coenzymes

• Organic molecules that exist in minute quantities in food– Essential vitamins must be obtained by diet

• Classifications– Fat soluble: Vitamins A,D,E,K– Water-soluble: B and C

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Minerals

• Inorganic

• Necessary for normal metabolic functions

• Functions– Establish resting membrane potentials, generate

action potentials, add strength to bones and teeth, buffers, involved in osmotic balance

• Obtained from animal and plant sources

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Metabolism

• Total of all chemical changes that occur in body– Anabolism: Energy-requiring process where

small molecules joined to form larger molecules

– Catabolism: Energy-releasing process where large molecules broken down to smaller

• Energy in carbohydrates, lipids, proteins is used to produce ATP through oxidation-reduction reactions

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Catabolic and Anabolic Reactions

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Cellular Metabolism

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Carbohydrate Metabolism

• Glycolysis– Breakdown of glucose into 2 pyruvic acid

molecules

• Phases– Input of ATP– Sugar cleavage– NADH production– ATP and pyruvic acid production

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Glycolysis

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Glycolysis

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Anaerobic Respiration• Breakdown of glucose

in absence of oxygen– Produces 2 molecules

of lactic acid and 2 molecules of ATP

• Phases– Glycolysis– Lactic acid formation

• Cori cycle– Process of converting

lactic acid to glucose

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Aerobic Respiration

• Breakdown of glucose in presence of oxygen to produce carbon dioxide, water, 38 ATP molecules– Most of ATP molecules to sustain life are

produced this way

• Phases– Glycolysis, acetyl-CoA formation, citric acid

cycle, electron-transport chain

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Aerobic Respiration

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Electron-Transport Chain

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Lipid Metabolism

• Adipose triglycerides are broken down and released as free fatty acids

• Free fatty acids are taken up by cells and broken down by beta-oxidation into acetyl-CoA which– Can enter citric acid

cycle

– Can be converted to ketone bodies

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Protein Metabolism

• New amino acids are formed by transamination, transfer of an amine group to keto acid

• Amino acids are used to synthesize proteins– If used for energy, ammonia is produced as a

by-product of oxidative deamination• Ammonia is converted to urea and excreted

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Amino Acid Metabolism

• Once absorbed in body, amino acids quickly taken up by cells

• Amino acids are used to synthesize proteins or as a source of energy

• Amino acids not stored in body

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Amino Acid Reactions

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Interconversion of Nutrient Molecules

• Glycogenesis– Excess glucose used to form glycogen

• Lipogenesis– When glycogen stores filled, glucose and amino acids

used to synthesize lipids

• Glycogenolysis– Breakdown of glycogen to glucose

• Gluconeogenesis– Formation of glucose from amino acids and glycerol

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Interconversion of Nutrient Molecules

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Metabolic States

• Absorptive state– Period immediately after eating when nutrients

absorbed through intestinal wall into circulatory and lymphatic systems (about 4 hours after each meal)

• Postabsorptive state– Occurs late in morning, afternoon, night after

absorptive state concluded– Blood glucose levels maintained by conversion

of other molecules to glucose

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Absorptive State

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Postabsorptive State

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Metabolic Rate

• Total amount of energy produced and used by body per unit of time– Estimated by amount of oxygen used per minute

• Components– Basal metabolic rate

• Energy used at rest, 60% of metabolic rate

– Thermic effect of food• Energy used to digest and absorb food, 10%

– Muscular activity• Energy used for muscle contraction, 30%

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Body Temperature Regulation

• A balance between heat gain and loss– Heat is produced through metabolism– Heat is exchanged through radiation,

conduction, convection, evaporation

• The greater the temperature difference between body and environment, the greater the rate of heat exchange

• Regulated by a “set point” in hypothalamus

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Heat Exchange

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Temperature Regulation