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Substrate Metabolism – Rest vs Stress 23/10/10 SP Notes Primary Notes - rest = basal metabolic rate + minimal exercise - major stress = 50% burn - aim = to preserve plasma glucose levels for brain metabolism. REST - least expensive form of energy production utilized: carbohydrate -> fat -> protein in decreasing ratios. Carbohydrate Sources - glucose, fructose & galactose from GI tract glycogen gluconeogenesis some amino acids (alanine + others) glycerol from triglycerides (1) (2) (3) (4) glucose enters the cell by insulin promoted facilitated diffusion with a Na+ contransporter. phosphorylated to glucose-6-phosphate forms 2 pyruvates -> transported into matrix of mitochondria converted into ACoA -> enters the Citric acid cycle -> oxidative phosphorylation. Protein - proteins broken down to aa's (liver) - leucine, isoleucine, phenylalanine & tryrosine = ketogenic -> produce acetoacetate - alanine + others are glucogenic or gluconeogenic Fat (1) triglycerides -> hydrolysed to FFAs & glycerol (2) transported to tissues (3) glycerol -> glycerol-3-phosphate & enters glycolytic pathway (4) FFA's transported to mitochondria by carnitine carrier -> degraded to ACoA (betaoxidation) -> enters the citric acid cycle. - essential fatty acids = linolenic, linoleic & arachidonic acid - used in the production of leukotrienes, prostaglandins, prostacyclin. Jeremy Fernando (2011) STRESS - increase in basal metabolism proportional to the degree of sepsis/trauma/burn - if metabolic needs aren’t met -> the patient will mobilize protein, fat and carbohydrate to meet metabolic demand - most hospitalized patients require 25/30kcal/kg/day - mechanically ventilated are on the lower aspect of range - burns and trauma patient may require 45kcal/kg/day - loss of whole body water and protein reduction in protein synthesis and increased degradation rapid catabolic muscle wasting -> reduction in cross-sectional area of muscle fibers 50% decline in respiratory and skeletal muscle function (in first 2 weeks) Sepsis - resting energy expenditure increases by 40% - increased plasma glucose - cytokines increase glucose membrane transporter (non-insulin mediated) -> saturate Citric acid cycle -> increase lactate production. - catabolic state Burns - 60% burns doubles the resting energy expenditure - catabolic state mediated by cortisol - decreased protein synthesis in muscles Trauma - protein catabolism increased resting energy expenditure increased in catabolic hormones (adrenaline & norad) -> glucose turnover increases. feed enterally soon if possible MANAGEMENT - provision of high quality amino acids along with insulin - feed appropriately Jeremy Fernando (2011)