Download Substrate Metabolism – Rest vs Stress

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)