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Transcript
Nutrition, Metabolism, and Body Temperature Regulation 24 Part A Chapter 24: Nutrition, Metabolism, and Temperature 1 Nutrition Nutrient – a substance that promotes normal growth, maintenance, and repair Major nutrients – carbohydrates, lipids, and proteins Other nutrients – vitamins and minerals (and technically speaking, water) Chapter 24: Nutrition, Metabolism, and Temperature 2 Nutrition Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.1 3 Carbohydrates Complex carbohydrates (starches) are found in bread, cereal, flour, pasta, nuts, and potatoes Simple carbohydrates (sugars) are found in soft drinks, candy, fruit, and ice cream Glucose is the molecule ultimately used by body cells to make ATP Neurons and RBCs rely almost entirely upon glucose to supply their energy needs Excess glucose is converted to glycogen or fat and stored Chapter 24: Nutrition, Metabolism, and Temperature 4 Carbohydrates The minimum amount of carbohydrates needed to maintain adequate blood glucose levels is 100 grams per day Starchy foods and milk have nutrients such as vitamins and minerals in addition to complex carbohydrates Refined carbohydrate foods (candy and soft drinks) provide energy sources only and are referred to as “empty calories” Chapter 24: Nutrition, Metabolism, and Temperature 5 Lipids The most abundant dietary lipids, triglycerides, are found in both animal and plant foods Essential fatty acids – linoleic and linolenic acid, found in most vegetables, must be ingested Dietary fats: Help the body to absorb vitamins Are a major energy fuel of hepatocytes and skeletal muscle Are a component of myelin sheaths and all cell membranes Chapter 24: Nutrition, Metabolism, and Temperature 6 Lipids Fatty deposits in adipose tissue provide: A protective cushion around body organs An insulating layer beneath the skin An easy-to-store concentrated source of energy Chapter 24: Nutrition, Metabolism, and Temperature 7 Lipids Prostaglandins function in: Smooth muscle contraction Control of blood pressure Inflammation Cholesterol stabilizes membranes and is a precursor of bile salts and steroid hormones Chapter 24: Nutrition, Metabolism, and Temperature 8 Lipids: Dietary Requirements Higher for infants and children than for adults The American Heart Association suggests that: Fats should represent less than 30% of one’s total caloric intake Saturated fats should be limited to 10% or less of one’s total fat intake Daily cholesterol intake should not exceed 200 mg Chapter 24: Nutrition, Metabolism, and Temperature 9 Proteins Complete proteins that meet all the body’s amino acid needs are found in eggs, milk, milk products, meat, and fish Incomplete proteins are found in legumes, nuts, seeds, grains, and vegetables Chapter 24: Nutrition, Metabolism, and Temperature 10 Proteins Proteins supply: Essential amino acids, the building blocks for nonessential amino acids Nitrogen for nonprotein nitrogen-containing substances Daily intake should be approximately 0.8g/kg of body weight Chapter 24: Nutrition, Metabolism, and Temperature 11 Proteins: Synthesis and Hydrolysis All-or-none rule All amino acids needed must be present at the same time for protein synthesis to occur Adequacy of caloric intake Protein will be used as fuel if there is insufficient carbohydrate or fat available Chapter 24: Nutrition, Metabolism, and Temperature 12 Proteins: Synthesis and Hydrolysis Nitrogen balance The rate of protein synthesis equals the rate of breakdown and loss Positive – synthesis exceeds breakdown (normal in children and tissue repair) Negative – breakdown exceeds synthesis (e.g., stress, burns, infection, or injury) Hormonal control Anabolic hormones accelerate protein synthesis Chapter 24: Nutrition, Metabolism, and Temperature 13 Vitamins Organic compounds needed for growth and good health They are crucial in helping the body use nutrients and often function as coenzymes Only vitamins D, K, and B are synthesized in the body; all others must be ingested Water-soluble vitamins (B-complex and C) are absorbed in the gastrointestinal tract B12 additionally requires gastric intrinsic factor to be absorbed Chapter 24: Nutrition, Metabolism, and Temperature 14 Vitamins Fat-soluble vitamins (A, D, E, and K) bind to ingested lipids and are absorbed with their digestion products Vitamins A, C, and E also act in an antioxidant cascade Chapter 24: Nutrition, Metabolism, and Temperature 15 Minerals Seven minerals are required in moderate amounts Calcium, phosphorus, potassium, sulfur, sodium, chloride, and magnesium Dozens are required in trace amounts Minerals work with nutrients to ensure proper body functioning Calcium, phosphorus, and magnesium salts harden bone Chapter 24: Nutrition, Metabolism, and Temperature 16 Minerals Sodium and chloride help maintain normal osmolarity, water balance, and are essential in nerve and muscle function Uptake and excretion must be balanced to prevent toxic overload Chapter 24: Nutrition, Metabolism, and Temperature 17 Metabolism Metabolism – all chemical reactions necessary to maintain life Cellular respiration – food fuels are broken down within cells and some of the energy is captured to produce ATP Anabolic reactions – synthesis of larger molecules from smaller ones Catabolic reactions – hydrolysis of complex structures into simpler ones Chapter 24: Nutrition, Metabolism, and Temperature 18 Metabolism Enzymes shift the high-energy phosphate groups of ATP to other molecules These phosphorylated molecules are activated to perform cellular functions Chapter 24: Nutrition, Metabolism, and Temperature 19 Stages of Metabolism Energy-containing nutrients are processed in three major stages Digestion – breakdown of food; nutrients are transported to tissues Anabolism and formation of catabolic intermediates where nutrients are: Built into lipids, proteins, and glycogen Broken down by catabolic pathways to pyruvic acid and acetyl CoA Oxidative breakdown – nutrients are catabolized to carbon dioxide, water, and ATP Chapter 24: Nutrition, Metabolism, and Temperature 20 Stages of Metabolism Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.3 21 Oxidation-Reduction (Redox) Reactions Oxidation occurs via the gain of oxygen or the loss of hydrogen Whenever one substance is oxidized, another substance is reduced Oxidized substances lose energy Reduced substances gain energy Coenzymes act as hydrogen (or electron) acceptors Two important coenzymes are nicotinamide adenine dinucleotide (NAD+) and flavin adenine dinucleotide (FAD) Chapter 24: Nutrition, Metabolism, and Temperature 22 Mechanisms of ATP Synthesis: Substrate-Level Phosphorylation High-energy phosphate groups are transferred directly from phosphorylated substrates to ADP ATP is synthesized via substrate-level phosphorylation in glycolysis and the Krebs cycle Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.4a 23 Mechanisms of ATP Synthesis: Oxidative Phosphorylation Uses the chemiosmotic process whereby the movement of substances across a membrane is coupled to chemical reactions Chapter 24: Nutrition, Metabolism, and Temperature 24 Mechanisms of ATP Synthesis: Oxidative Phosphorylation Is carried out by the electron transport proteins in the cristae of the mitochondria Nutrient energy is used to pump hydrogen ions into the intermembrane space A steep diffusion gradient across the membrane results When hydrogen ions flow back across the membrane through ATP synthase, energy is captured and attaches phosphate groups to ADP (to make ATP) Chapter 24: Nutrition, Metabolism, and Temperature 25 Mechanisms of ATP Synthesis: Oxidative Phosphorylation Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.4b 26 Carbohydrate Metabolism Since all carbohydrates are transformed into glucose, it is essentially glucose metabolism Oxidation of glucose is shown by the overall reaction: C6H12O6 + 6O2 6H2O + 6CO2 + 36 ATP + heat Glucose is catabolized in three pathways Glycolysis Krebs cycle The electron transport chain and oxidative phosphorylation Chapter 24: Nutrition, Metabolism, and Temperature 27 Carbohydrate Catabolism Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.5 28 Glycolysis A three-phase pathway in which: Glucose is oxidized into pyruvic acid NAD+ is reduced to NADH + H+ ATP is synthesized by substrate-level phosphorylation Pyruvic acid: Moves on to the Krebs cycle in an aerobic pathway Is reduced to lactic acid in an anaerobic environment Chapter 24: Nutrition, Metabolism, and Temperature 29 Glycolysis Chapter 24: Nutrition, Metabolism, and Temperature 30 Figure 24.6 Glycolysis: Phase 1 and 2 Phase 1: Sugar activation Two ATP molecules activate glucose into fructose-1,6-diphosphate Phase 2: Sugar cleavage Fructose-1,6-bisphosphate is cleaved into two 3-carbon isomers Bishydroxyacetone phosphate Glyceraldehyde 3-phosphate Chapter 24: Nutrition, Metabolism, and Temperature 31 Glycolysis: Phase 3 Phase 3: Oxidation and ATP formation The 3-carbon sugars are oxidized (reducing NAD+) Inorganic phosphate groups (Pi) are attached to each oxidized fragment The terminal phosphates are cleaved and captured by ADP to form four ATP molecules Chapter 24: Nutrition, Metabolism, and Temperature 32 Glycolysis: Phase 3 The final products are: Two pyruvic acid molecules Two NADH + H+ molecules (reduced NAD+) A net gain of two ATP molecules Chapter 24: Nutrition, Metabolism, and Temperature 33 Krebs Cycle: Preparatory Step Occurs in the mitochondrial matrix and is fueled by pyruvic acid and fatty acids Chapter 24: Nutrition, Metabolism, and Temperature 34 Krebs Cycle: Preparatory Step Pyruvic acid is converted to acetyl CoA in three main steps: Decarboxylation Carbon is removed from pyruvic acid Carbon dioxide is released Chapter 24: Nutrition, Metabolism, and Temperature 35 Krebs Cycle: Preparatory Step Oxidation Hydrogen atoms are removed from pyruvic acid NAD+ is reduced to NADH + H+ Formation of acetyl CoA – the resulting acetic acid is combined with coenzyme A, a sulfur-containing coenzyme, to form acetyl CoA Chapter 24: Nutrition, Metabolism, and Temperature 36 Krebs Cycle An eight-step cycle in which each acetic acid is decarboxylated and oxidized, generating: Three molecules of NADH + H+ One molecule of FADH2 Two molecules of CO2 One molecule of ATP For each molecule of glucose entering glycolysis, two molecules of acetyl CoA enter the Krebs cycle PLAY Krebs Cycle Chapter 24: Nutrition, Metabolism, and Temperature 37 Krebs Cycle Chapter 24: Nutrition, Metabolism, and Temperature 38 24.7 Figure Electron Transport Chain Food (glucose) is oxidized and the released hydrogens: Are transported by coenzymes NADH and FADH2 Enter a chain of proteins bound to metal atoms (cofactors) Combine with molecular oxygen to form water Release energy The energy released is harnessed to attach inorganic phosphate groups (Pi) to ADP, making ATP by oxidative phosphorylation Chapter 24: Nutrition, Metabolism, and Temperature 39 Mechanism of Oxidative Phosphorylation The hydrogens delivered to the chain are split into protons (H+) and electrons The protons are pumped across the inner mitochondrial membrane by: NADH dehydrogenase (FMN, Fe-S) Cytochrome b-c1 Cytochrome oxidase (a-a3) The electrons are shuttled from one acceptor to the next Chapter 24: Nutrition, Metabolism, and Temperature 40 Mechanism of Oxidative Phosphorylation Electrons are delivered to oxygen, forming oxygen ions Oxygen ions attract H+ to form water H+ pumped to the intermembrane space: Diffuses back to the matrix via ATP synthase Releases energy to make ATP PLAY InterActive Physiology®: Muscular System: Muscular Metabolism Chapter 24: Nutrition, Metabolism, and Temperature 41 Mechanism of Oxidative Phosphorylation Chapter 24: Nutrition, Metabolism, and Temperature Figure 42 24.8 Electronic Energy Gradient The transfer of energy from NADH + H+ and FADH2 to oxygen releases large amounts of energy This energy is released in a stepwise manner through the electron transport chain Chapter 24: Nutrition, Metabolism, and Temperature 43 Electronic Energy Gradient The electrochemical proton gradient across the inner membrane: Creates a pH gradient Generates a voltage gradient These gradients cause H+ to flow back into the matrix via ATP synthase PLAY Electron Transport Chapter 24: Nutrition, Metabolism, and Temperature 44 Electronic Energy Gradient Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.9 45 ATP Synthase The enzyme consists of three parts: a rotor, a knob, and a rod Current created by H+ causes the rotor and rod to rotate This rotation activates catalytic sites in the knob where ADP and Pi are combined to make ATP Chapter 24: Nutrition, Metabolism, and Temperature 46 Structure of ATP Synthase Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.10 47 Summary of ATP Production Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.11 48 Glycogenesis and Glycogenolysis Glycogenesis – formation of glycogen when glucose supplies exceed cellular need for ATP synthesis Glycogenolysis – breakdown of glycogen in response to low blood glucose Chapter 24: Nutrition, Metabolism, and Temperature 49 Figure 24.12 Gluconeogenesis The process of forming sugar from noncarbohydrate molecules Takes place mainly in the liver Protects the body, especially the brain, from the damaging effects of hypoglycemia by ensuring ATP synthesis can continue Chapter 24: Nutrition, Metabolism, and Temperature 50 Lipid Metabolism Most products of fat metabolism are transported in lymph as chylomicrons Lipids in chylomicrons are hydrolyzed by plasma enzymes and absorbed by cells Only neutral fats are routinely oxidized for energy Catabolism of fats involves two separate pathways Glycerol pathway Fatty acids pathway Chapter 24: Nutrition, Metabolism, and Temperature 51 Lipid Metabolism Glycerol is converted to glyceraldehyde phosphate Glyceraldehyde is ultimately converted into acetyl CoA Acetyl CoA enters the Krebs cycle Fatty acids undergo beta oxidation which produces: Two-carbon acetic acid fragments, which enter the Krebs cycle Reduced coenzymes, which enter the electron transport chain Chapter 24: Nutrition, Metabolism, and Temperature 52 Lipid Metabolism Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.13 53 Lipogenesis and Lipolysis Excess dietary glycerol and fatty acids undergo lipogenesis to form triglycerides Glucose is easily converted into fat since acetyl CoA is: An intermediate in glucose catabolism The starting molecule for the synthesis of fatty acids Chapter 24: Nutrition, Metabolism, and Temperature 54 Lipogenesis and Lipolysis Lipolysis, the breakdown of stored fat, is essentially lipogenesis in reverse Oxaloacetic acid is necessary for the complete oxidation of fat Without it, acetyl CoA is converted into ketones (ketogenesis) Chapter 24: Nutrition, Metabolism, and Temperature 55 Lipogenesis and Lipolysis Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.14 56 Lipid Metabolism: Synthesis of Structural Materials Phospholipids are important components of myelin and cell membranes Chapter 24: Nutrition, Metabolism, and Temperature 57 Lipid Metabolism: Synthesis of Structural Materials The liver: Synthesizes lipoproteins for transport of cholesterol and fats Makes tissue factor, a clotting factor Synthesizes cholesterol for acetyl CoA Uses cholesterol to form bile salts Certain endocrine organs use cholesterol to synthesize steroid hormones Chapter 24: Nutrition, Metabolism, and Temperature 58 Protein Metabolism Excess dietary protein results in amino acids being: Oxidized for energy Converted into fat for storage Amino acids must be deaminated prior to oxidation for energy Chapter 24: Nutrition, Metabolism, and Temperature 59 Protein Metabolism Deaminated amino acids are converted into: Pyruvic acid One of the keto acid intermediates of the Krebs cycle These events occur as transamination, oxidative deamination, and keto acid modification Chapter 24: Nutrition, Metabolism, and Temperature 60 Nutrition, Metabolism, and Body Temperature Regulation 24 Part B Chapter 24: Nutrition, Metabolism, and Temperature 61 Oxidation of Amino Acids Transamination – switching of an amine group from an amino acid to a keto acid (usually -ketoglutaric acid of the Krebs cycle) Typically, glutamic acid is formed in this process Chapter 24: Nutrition, Metabolism, and Temperature 62 Oxidation of Amino Acids Oxidative deamination – the amine group of glutamic acid is: Released as ammonia Combined with carbon dioxide in the liver Excreted as urea by the kidneys Keto acid modification – keto acids from transamination are altered to produce metabolites that can enter the Krebs cycle Chapter 24: Nutrition, Metabolism, and Temperature 63 Synthesis of Proteins Amino acids are the most important anabolic nutrients, and they form: All protein structures The bulk of the body’s functional molecules Chapter 24: Nutrition, Metabolism, and Temperature 64 Synthesis of Proteins Amounts and types of proteins: Are hormonally controlled Reflect each life cycle stage A complete set of amino acids is necessary for protein synthesis All essential amino acids must be provided in the diet Chapter 24: Nutrition, Metabolism, and Temperature 65 Summary: Carbohydrate Metabolic Reactions Chapter 24: Nutrition, Metabolism, and Temperature Table 24.2.1 66 Summary: Lipid and Protein Metabolic Reactions Chapter 24: Nutrition, Metabolism, and Temperature Table 24.2.2 67 State of the Body The body exists in a dynamic catabolic-anabolic state Organic molecules (except DNA) are continuously broken down and rebuilt The body’s total supply of nutrients constitutes its nutrient pool Chapter 24: Nutrition, Metabolism, and Temperature 68 State of the Body Amino acid pool – body’s total supply of free amino acids is the source for: Resynthesizing body proteins Forming amino acid derivatives Gluconeogenesis Chapter 24: Nutrition, Metabolism, and Temperature 69 Carbohydrate/Fat and Amino Acid Pools Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.16 70 Interconversion Pathways of Nutrients Carbohydrates are easily and frequently converted into fats Their pools are linked by key intermediates They differ from the amino acid pool in that: Fats and carbohydrates are oxidized directly to produce energy Excess carbohydrate and fat can be stored Chapter 24: Nutrition, Metabolism, and Temperature 71 Interconversion Pathways of Nutrients Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.17 72 Absoprtive and Postabsorptive States Metabolic controls equalize blood concentrations of nutrients between two states Absorptive The time during and shortly after nutrient intake Postabsorptive The time when the GI tract is empty Energy sources are supplied by the breakdown of body reserves Chapter 24: Nutrition, Metabolism, and Temperature 73 Absoprtive State The major metabolic thrust is anabolism and energy storage Amino acids become proteins Glycerol and fatty acids are converted to triglycerides Glucose is stored as glycogen Dietary glucose is the major energy fuel Excess amino acids are deaminated and used for energy or stored as fat in the liver Chapter 24: Nutrition, Metabolism, and Temperature 74 Absoprtive State Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.18a 75 Principal Pathways of the Absorptive State In muscle: Amino acids become protein Glucose is converted to glycogen In the liver: Amino acids become protein or are deaminated to keto acids Glucose is stored as glycogen or converted to fat Chapter 24: Nutrition, Metabolism, and Temperature 76 Principal Pathways of the Absorptive State In adipose tissue: Glucose and fats are converted and stored as fat All tissues use glucose to synthesize ATP Chapter 24: Nutrition, Metabolism, and Temperature 77 Principal Pathways of the Absorptive State Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.18b 78 Insulin Effects on Metabolism Insulin controls the absorptive state and its secretion is stimulated by: Increased blood glucose Elevated amino acid levels in the blood Gastrin, CCK, and secretin Insulin enhances: Active transport of amino acids into tissue cells Facilitated diffusion of glucose into tissue Chapter 24: Nutrition, Metabolism, and Temperature 79 Insulin Effects on Metabolism Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.19 80 Diabetes Mellitus A consequence of inadequate insulin production or abnormal insulin receptors Glucose becomes unavailable to most body cells Metabolic acidosis, protein wasting, and weight loss result as fats and tissue proteins are used for energy Chapter 24: Nutrition, Metabolism, and Temperature 81 Postabsorptive State The major metabolic thrust is catabolism and replacement of fuels in the blood Proteins are broken down to amino acids Triglycerides are turned into glycerol and fatty acids Glycogen becomes glucose Glucose is provided by glycogenolysis and gluconeogenesis Fatty acids and ketones are the major energy fuels Amino acids are converted to glucose in the liver Chapter 24: Nutrition, Metabolism, and Temperature 82 Postabsorptive State Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.20a 83 Principle Pathways in the Postabsorptive State In muscle: Protein is broken down to amino acids Glycogen is converted to ATP and pyruvic acid (lactic acid in anaerobic states) Chapter 24: Nutrition, Metabolism, and Temperature 84 Principle Pathways in the Postabsorptive State In the liver: Amino acids, pyruvic acid, stored glycogen, and fat are converted into glucose Fat is converted into keto acids that are used to make ATP Fatty acids (from adipose tissue) and ketone bodies (from the liver) are used in most tissue to make ATP Glucose from the liver is used by the nervous system to generate ATP Chapter 24: Nutrition, Metabolism, and Temperature 85 Principle Pathways in the Postabsorptive State Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.20b 86 Hormonal and Neural Controls of the Postabsorptive State Decreased plasma glucose concentration and rising amino acid levels stimulate alpha cells of the pancreas to secrete glucagon (the antagonist of insulin) Glucagon stimulates: Glycogenolysis and gluconeogenesis Fat breakdown in adipose tissue Glucose sparing Chapter 24: Nutrition, Metabolism, and Temperature 87 Hormonal and Neural Controls of the Postabsorptive State In response to low plasma glucose, the sympathetic nervous system releases epinephrine, which acts on the liver, skeletal muscle, and adipose tissue to mobilize fat and promote glycogenolysis Chapter 24: Nutrition, Metabolism, and Temperature 88 Liver Metabolism Hepatocytes carry out over 500 intricate metabolic functions Chapter 24: Nutrition, Metabolism, and Temperature 89 Liver Metabolism A brief summary of liver functions Packages fatty acids to be stored and transported Synthesizes plasma proteins Forms nonessential amino acids Converts ammonia from deamination to urea Stores glucose as glycogen, and regulates blood glucose homeostasis Stores vitamins, conserves iron, degrades hormones, and detoxifies substances Chapter 24: Nutrition, Metabolism, and Temperature 90 Cholesterol Is the structural basis of bile salts, steroid hormones, and vitamin D Makes up part of the hedgehog molecule that directs embryonic development Is transported to and from tissues via lipoproteins Chapter 24: Nutrition, Metabolism, and Temperature 91 Cholesterol Lipoproteins are classified as: HDLs – high-density lipoproteins have more protein content LDLs – low-density lipoproteins have a considerable cholesterol component VLDLs – very low density lipoproteins are mostly triglycerides Chapter 24: Nutrition, Metabolism, and Temperature 92 Cholesterol Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.22 93 Lipoproteins The liver is the main source of VLDLs, which transport triglycerides to peripheral tissues (especially adipose) LDLs transport cholesterol to the peripheral tissues and regulate cholesterol synthesis HDLs transport excess cholesterol from peripheral tissues to the liver Also serve the needs of steroid-producing organs (ovaries and adrenal glands) Chapter 24: Nutrition, Metabolism, and Temperature 94 Lipoproteins High levels of HDL are thought to protect against heart attack High levels of LDL, especially lipoprotein (a), increase the risk of heart attack Chapter 24: Nutrition, Metabolism, and Temperature 95 Plasma Cholesterol Levels The liver produces cholesterol: At a basal level of cholesterol regardless of dietary intake Via a negative feedback loop involving serum cholesterol levels In response to saturated fatty acids Chapter 24: Nutrition, Metabolism, and Temperature 96 Plasma Cholesterol Levels Fatty acids regulate excretion of cholesterol Unsaturated fatty acids enhance excretion Saturated fatty acids inhibit excretion Certain unsaturated fatty acids (omega-3 fatty acids, found in cold-water fish) lower the proportions of saturated fats and cholesterol Chapter 24: Nutrition, Metabolism, and Temperature 97 Non-Dietary Factors Affecting Cholesterol Stress, cigarette smoking, and coffee drinking increase LDL levels Aerobic exercise increases HDL levels Body shape is correlated with cholesterol levels Fat carried on the upper body is correlated with high cholesterol levels Fat carried on the hips and thighs is correlated with lower levels Chapter 24: Nutrition, Metabolism, and Temperature 98 Body Energy Balance Bond energy released from catabolized food must equal the total energy output Energy intake – equal to the energy liberated during the oxidation of food Energy output includes the energy: Immediately lost as heat (about 60% of the total) Used to do work (driven by ATP) Stored in the form of fat and glycogen Chapter 24: Nutrition, Metabolism, and Temperature 99 Body Energy Balance Nearly all energy derived from food is eventually converted to heat Cells cannot use this energy to do work, but the heat: Warms the tissues and blood Helps maintain the homeostatic body temperature Allows metabolic reactions to occur efficiently Chapter 24: Nutrition, Metabolism, and Temperature 100 Regulation of Food Intake When energy intake and energy outflow are balanced, body weight remains stable The hypothalamus releases peptides that influence feeding behavior Orexins are powerful appetite enhancers Neuropeptide Y causes a craving for carbohydrates Galanin produces a craving for fats GLP-1 and serotonin make us feel full and satisfied Chapter 24: Nutrition, Metabolism, and Temperature 101 Feeding Behaviors Feeding behavior and hunger depend on one or more of five factors Neural signals from the digestive tract Bloodborne signals related to the body energy stores Hormones, body temperature, and psychological factors Chapter 24: Nutrition, Metabolism, and Temperature 102 Nutrient Signals Related to Energy Stores High plasma levels of nutrients that signal depressed eating Plasma glucose levels Amino acids in the plasma Fatty acids and leptin Chapter 24: Nutrition, Metabolism, and Temperature 103 Hormones, Temperature, and Psychological Factors Glucagon and epinephrine stimulate hunger Insulin and cholecystokinin depress hunger Increased body temperature may inhibit eating behavior Psychological factors that have little to do with caloric balance can also influence eating behaviors Chapter 24: Nutrition, Metabolism, and Temperature 104 Control of Feeding Behavior and Satiety Leptin, secreted by fat tissue, appears to be the overall satiety signal Acts on the ventromedial hypothalamus Controls appetite and energy output Suppresses the secretion of neuropeptide Y, a potent appetite stimulant Blood levels of insulin and glucocorticoids play a role in regulating leptin release Chapter 24: Nutrition, Metabolism, and Temperature 105 Control of Feeding Behavior and Satiety Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.23 106 Metabolic Rate Rate of energy output (expressed per hour) equal to the total heat produced by: All the chemical reactions in the body The mechanical work of the body Measured directly with a calorimeter or indirectly with a respirometer Chapter 24: Nutrition, Metabolism, and Temperature 107 Metabolic Rate Basal metabolic rate (BMR) Reflects the energy the body needs to perform its most essential activities Total metabolic rate (TMR) Total rate of kilocalorie consumption to fuel all ongoing activities Chapter 24: Nutrition, Metabolism, and Temperature 108 Factors that Influence BMR Surface area, age, gender, stress, and hormones As the ratio of surface area to volume increases, BMR increases Males have a disproportionately high BMR Stress increases BMR Thyroxine increases oxygen consumption, cellular respiration, and BMR Chapter 24: Nutrition, Metabolism, and Temperature 109 Regulation of Body Temperature Body temperature – balance between heat production and heat loss At rest, the liver, heart, brain, and endocrine organs account for most heat production During vigorous exercise, heat production from skeletal muscles can increase 30–40 times Normal body temperature is 36.2C (98.2F); optimal enzyme activity occurs at this temperature Temperature spikes above this range denature proteins and depress neurons Chapter 24: Nutrition, Metabolism, and Temperature 110 Regulation of Body Temperature Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.25 111 Core and Shell Temperature Organs in the core (within the skull, thoracic, and abdominal cavities) have the highest temperature The shell, essentially the skin, has the lowest temperature Blood serves as the major agent of heat transfer between the core and shell Core temperature remains relatively constant, while shell temperature fluctuates substantially (20C– 40C) Chapter 24: Nutrition, Metabolism, and Temperature 112 Mechanisms of Heat Exchange The body uses four mechanisms of heat exchange Radiation – loss of heat in the form of infrared rays Conduction – transfer of heat by direct contact Convection – transfer of heat to the surrounding air Evaporation – heat loss due to the evaporation of water from the lungs, mouth mucosa, and skin (insensible heat loss) Evaporative heat loss becomes sensible when body temperature rises and sweating produces increased water for vaporization Chapter 24: Nutrition, Metabolism, and Temperature 113 Role of the Hypothalamus The main thermoregulation center is the preoptic region of the hypothalamus The heat-loss and heat-promoting centers comprise the thermoregulatory centers The hypothalamus: Receives input from thermoreceptors in the skin and core Responds by initiating appropriate heat-loss and heat-promoting activities Chapter 24: Nutrition, Metabolism, and Temperature 114 Heat-Promoting Mechanisms Low external temperature or low temperature of circulating blood activates heat-promoting centers of the hypothalamus to cause: Vasoconstriction of cutaneous blood vessels Increased metabolic rate Shivering Enhanced thyroxine release Chapter 24: Nutrition, Metabolism, and Temperature 115 Heat-Loss Mechanisms When the core temperature rises, the heat-loss center is activated to cause: Vasodilation of cutaneous blood vessels Enhanced sweating Voluntary measures commonly taken to reduce body heat include: Reducing activity and seeking a cooler environment Wearing light-colored and loose-fitting clothing Chapter 24: Nutrition, Metabolism, and Temperature 116 Mechanisms of Body Temperature Regulation Chapter 24: Nutrition, Metabolism, and Temperature Figure 24.27 117 Hyperthermia Normal heat loss processes become ineffective and elevated body temperatures depress the hypothalamus This sets up a positive-feedback mechanism, sharply increasing body temperature and metabolic rate This condition, called heat stroke, can be fatal if not corrected Chapter 24: Nutrition, Metabolism, and Temperature 118 Heat Exhaustion Heat-associated collapse after vigorous exercise, evidenced by elevated body temperature, mental confusion, and fainting Due to dehydration and low blood pressure Heat-loss mechanisms are fully functional Can progress to heat stroke if the body is not cooled and rehydrated Chapter 24: Nutrition, Metabolism, and Temperature 119 Fever Controlled hyperthermia, often a result of infection, cancer, allergic reactions, or central nervous system injuries White blood cells, injured tissue cells, and macrophages release pyrogens that act on the hypothalamus, causing the release of prostaglandins Prostaglandins reset the hypothalamic thermostat The higher set point is maintained until the natural body defenses reverse the disease process Chapter 24: Nutrition, Metabolism, and Temperature 120 Developmental Aspects Good nutrition is essential in utero as well as throughout life Lack of proteins needed for fetal growth and in the first three years of life can lead to mental deficits and learning disorders With the exception of insulin-dependent diabetes mellitus, children free of genetic disorders rarely exhibit metabolic problems In later years, non-insulin-dependent diabetes mellitus becomes a major problem Chapter 24: Nutrition, Metabolism, and Temperature 121 Developmental Aspects Many agents prescribed for age-related medical problems influence nutrition Diuretics can cause hypokalemia by promoting potassium loss Antibiotics can interfere with food absorption Mineral oil interferes with absorption of fat-soluble vitamins Excessive alcohol consumption leads to malabsorption problems, certain vitamin and mineral deficiencies, deranged metabolism, and damage to the liver and pancreas Chapter 24: Nutrition, Metabolism, and Temperature 122