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Unit 7 - Metabolism and Energy Balance - Full Textbook Notes

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University of Waterloo
BIOL 373
Heidi Engelhardt

METABOLISM AND ENERGY BALANCECHAPTER 22Appetite and SatietyFeeding centre tonically activeSatiety centre stops food intake by inhibiting feeding centre Theories of homestatic food intake Glucostatic theory glucose metabolism by hypothalamic centers regulates food intake When blood glucose concentrations decrease the satiety centre is suppressed and the feeding centre is dominant When the glucose metabolism increases the satiety center inhibits the feeding centerLipostatic theory a signal from the bodys fat stores to the brain modulates eating behaviour so the body maintains a particular weight If fat stores are increased then eating decreases In times of starvation eating increases Obesity is caused from a disruption in this pathway Leptin protein hormone synthesized in adipocytes under control of ob obese gene acts as negative feedback signal between adipose tissue and brain increase in fat storesadipose cells secrete lepinfood intake decreases Neuropeptide Y NPY brain neurotransmitter stimulus for food intake Leptin inhibits NPY in negative feedback pathway Ghrelin peptide secreted by stomach during fasting and increases hunger CCK and GLP1 released by gut during a meal to help decrease hunger Psychological factors that regulate food intake stress anorexia nervosaEnergy BalanceFirst law of thermodynamics the total amount of energy in the universe is constantall energy that goes into a biological system can be accounted for Energy intake energy in nutrients we eat digest absorbEnergy output combination of work performed and energy returned to the environment as heat Transport work moves molecules from one side of membrane to the otherMechanical work uses intracellular fibres and filaments to create movement external skeletal muscle contraction internal cytoplasmic vesicles pumping the heartChemical work growth maintenance storage of information and energy Subdivided into synthesis and storage short term energy in high energy phosphate compounds like ATP and long term energy storage in chemical bonds of glycogen and fatOne kilocaloriethe amount of heat needed to raise the temperature of one liter of water by one degree Celsius Metabolic energy content of food is slightly less because most foods cannot be fully digested and absorbed Oxygen consumption most common method for estimating metabolic rate rate at which the body consumes oxygen as it metabolizes nutrients Ratio of CO2 produced to O2 consumed varies with composition of diet Metabolic rateL O2 consumed per day x kcal per L of O2Basal Metabolic Rate lowest metabolic rate measured when sleepingResting Metabolic Rate measured after a 12 hour fast of a person awake but restingFactors that affect metabolic rate age older people have slower metabolisms sex men have higher amount of lean muscle mass muscle has higher oxygen consumption than adipose activity level diet fats cause little dietinduced thermogenesis protein causes the most heat production hormones BMR is increased by thyroid hormones and catecholamines E and NE genetics We can only control energy intake and level of physical activity Cells convert glucose to glycogen for storage because it is a more compact form of energy and requires less water for hydration MetabolismMetabolism the sum of all chemical reactions in the body The reactions extract energy from nutrients use energy for work and store excess energy Anabolic pathways synthesize large molecules from smaller onesCatabolic breaks down large molecules into smaller ones Fed stateabsorptive state period of time following a meal when products of digestion are being absorbed used stored This is an anabolic state in which energy of nutrient biomolecules is transferred to highenergy compounds or stored in chemical bonds of other molecules Fasted statepostabsorptive state once nutrients from a recent meal are no longer in the bloodstream and available for use by tissues As the pool of available nutrients in blood decreases the body taps into its stored reserves This is a catabolic state because cells break down large molecules into smaller molecules energy released here is used to do work Energy biomolecules can be metabolized immediately with energy released from broken chemical bonds trapped in ATP phosphocreatine and other high energy compounds can be used to do mechanical work Synthesis biomolecules entering cells can be used to synthesize basic components needed for growth and maintenance of cells and tissues Storage if amount of food ingested exceeds bodys requirements for energy and synthesis excess energy goes into storage in bonds of glycogen and fat Storage makes energy available for times of fasting The fat of absorbed biomolecule depends on whether it is a carbohydrate protein or fat These go into nutrient pools available for immediate use located in plasma in body free fatty acid pool glucose pool amino acid pool Free fatty acid pool form primary pool of fats in blood They can be used as an energy source by many tissues but are easily storage as fat triglycerides in adipose tissueCarbohydrates absorbed mostly as glucose Glucose is only fuel the brain can metabolize conservation measure ensures the brain has access to an adequate energy supply Excess glucose goes into storage as glycogen by process of glycogenesis Glycogen stores are limited and additional excess glucose is converted to fat by lipogenesis If plasma glucose concentrations decrease the body converts glycogen to glucose through glycogenolysis The amino acid pool is used primarily for protein synthesis If glucose intake is low amino acids can be converted into glucose through gluconeogenesis Glycerol from triglycerides can also be used in this pathway Pushpull control regulate the flow of nutrients through metabolic pathways Enzyme activity must change to alter the net direction of the reaction During fed state insulin stimulates enzymes promoting glycogenesis glucose to glycogen and inhibits enzymes for glycogenolysis glycogen to glucosenet reaction is glycogen synthesis from glucoseDuring fasted state glucagon stimulates enzymes of glycogenolysis and inhibits enzymes for glycogenesisnet result is glucose synthesis from glycogen FedState MetabolismAnabolicabsorbed nutrients being used for energy synthesis and storage CarbohydratesGlycogen large polysaccharide main storage form of glucose glucose polymerby linking many individual glucose molecules together into a branched chain Glucose absorbed from intestine enters hepatic portal vein and taken to the liver where 30 is metabolized The remaining 70 continues in bloodstream to brain muscles organs and tissues Glucose moves from IF into cells by membrane GLUT transportersMost glucose absorbed goes immediately into glycolysis and the citric acid cycle to make ATP Some glucose is used by liver from lipoprotein synthesis Glucose that is not required for energy and synthesis is stored as glycogen or fat Glycogen stores are limited so excess is converted to triglycerides and stored in adipose tissue Glycogen in liver acts as main source of glucose for the body in periods between meals 4 hour supply of glucose stored as glycogen
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