Nutrients. Chapter 25 Nutrition, Metabolism, Temperature Regulation

Transcription

1 Chapter 25 Nutrition, Metabolism, Temperature Regulation 25-1 Nutrients Chemicals used by body to produce energy, provide building blocks or function in other chemical reactions Classes Carbohydrates, proteins, lipids, water: required in large amounts Vitamins, minerals: required in small amounts Food Guide Pyramid: USDA recommendations Essential nutrients: must be ingested, cannot be synthesized. Certain amino acids, certain fatty acids, most vitamins, minerals, water, and a minimum number of carbohydrates Kilocalories: measure of energy supplied by food and released through metabolism

2 Carbohydrates: Uses in the Body Digestion breaks poly- and disaccharides into monosaccharides before absorption Liver converts monosaccharides into glucose which is then used as an energy source to produce ATP Excess glucose converted to glycogen and stored in muscles and liver cells Excess beyond storage is converted to fat Sugars also become part of DNA, RNA, and ATP, glycoproteins, glycolipids 25-3 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 Linoleic acids: essential fatty acids. Found in seeds, nuts, legumes, grains and green leaves

3 Uses of Lipids in the Body Triglycerides: used to produce ATP Excess stored in adipose tissue or liver. Cholesterol: can be eaten or manufactured in the body. Component of plasma membranes, can be modified to form bile salts and steroids Eicosanoids derived from fatty acids. Involved in inflammation, blood clotting, tissue repair, smooth muscle contraction. Phospholipids: part of plasma membrane and used to construct the myelin sheath. Part of bile 25-5 Proteins Chains of amino acids Types Essential: must be obtained in diet Nonessential: body can synthesize Complete proteins: contain all necessary amino acids (meat, fish, poultry, milk, cheese, eggs) Functions Protection (antibodies), regulation (enzymes, hormones), structure (collagen), muscle contraction (actin, myosin), transportation (hemoglobin, ion channels)

4 Recommended Amounts Carbohydrates 60% of daily intake of kilocalories Lipids 30% or less of total daily kilocalories Proteins 10% of total kilocalories per day 25-7 Vitamins Function as coenzymes or parts of coenzymes (combine with enzymes and make the enzyme functional) Organic molecules that exist in minute quantities in food Essential vitamins must be obtained by diet Provitamins: substance that can be assembled by the body into a functioning vitamin. Classifications Fat soluble: A, D, E, K. Can be stored in fatty tissues to the point of toxicity. Too much A causes bone and muscle pain; skin disorders, hair loss, increased liver size. Too much D causes deposition of Ca in kidneys, heart, blood vessels. Water-soluble: B, C, and all others. Remain short time then are excreted. Too much C causes stomach inflammation; diarrhea. Antioxidants: prevent formation of free radicals. Free radicals are chemicals produced by metabolism that are missing electrons. They take electrons from chemicals in cells, damaging the cells

5 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; are components of coenzymes, vitamins, hemoglobin. Obtained from animal and plant sources. Minerals attached to plant fibers are difficult to absorb Daily Values Percent daily values related to energy consumption based on a 2000 kcal/day diet

6 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 oxidationreduction reactions 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

7 Aerobic Respiration Breakdown of glucose in presence of oxygen to produce carbon dioxide, water, 38 ATP molecules Most of ATP molecules that sustain life are produced this way Phases Citric acid cycle, electron-transport chain Aerobic Respiration

8 Aerobic Respiration Electron-Transport Chain

9 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 (ketogenesis) in liver. Ketones travel to skeletal muscle and are used in citric acid cycle to produce ATP Protein Metabolism Non-essential amino acids can be formed by transamination, transfer of an amine group to keto acid. Can also be eaten. Amino acids are used to synthesize proteins If used for energy, amino acids undergo oxidative deamination. Ammonia and keto acids are produced as by-products of oxidative deamination. Ammonia is converted to urea and excreted. Amino acids not stored in the body

10 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 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%

11 Body Temperature Regulation Free energy: total amount of energy liberated by the complete catabolism of food. 43% used to produce ATP 57% lost as heat A balance must be maintained between heat gain and loss Heat is produced through metabolism Heat is exchanged through radiation (loss of heat as infrared radiation), conduction (exchange of heat between objects in direct contact with each other), convection (transfer of heat between the body and the air), evaporation (conversion of water from a liquid to a gaseous form) The greater the temperature difference between body and environment, the greater the rate of heat exchange Regulated by a set point in hypothalamus. Negative feedback mechanism. Set point can change; e.g., during a fever