Energy homeostasis

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  • Energy homeostasis
    • Bomb calorimeter
      • a device for measuring the heat evolved in the combustion of a substance under constant-volume conditions
    • Energy potentials
      • Fat = 9.4kcal/g or 39.3kJ/g
      • Protein = 5.3kcal/g or 22.4kJ/g
      • CHO = 4.2kcal/g or 17.2kJ/g
    • Energy balance
      • energy expenditure
        • the energy the body expends to maintain its basic functions and to perform all levels of movement and activity
      • energy intake
        • dependent on diet, regulated by hunger and calorie consumption
      • the relationship between energy intake and energy expenditure
      • Positive energy balance
        • The amount of energy consumed in food exceeds the expenditure of energy, so excess is stored (adipose tissue)
      • Negative energy balance
        • the state in which energy intake is less than energy expended, resulting in weight loss
      • Neutral energy balance
        • The amount of energy consumed in food matches exactly the internal and external expenditure of energy
    • AMP-activated protein kinase
      • what does it stimulate
        • hypothalamus, heart and skeletal muscles
      • acts as key nutrient sensor and metabolic switch
      • what does it inhibit
        • pancreatic beta cells, liver and white adipose tissue
      • heterotrimer complex comprising of catalytic alpha subunit with serine/threonine protein kinase domain and 2 regulatory subunits (beta and gamma)
    • Respiratory Quotient (RQ)
      • RQ = VCO2/VO2
      • normal = 0.8, range = 0.67-1.3
    • Basal metabolic rate
      • Conditions needed to measure
        • 12hrs fast, good nights sleep, rest for at least 30mins before test, ambient temperature of around 25oC
      • 40kcal/hr/m2 or 166kJ/hr/m2
      • Influences
        • body SA and composition, age, gender, temperature, endocrine and nervous effects
      • How to measure
        • Calculations
          • (Revised) Harris-Benedict Equation - revised equation, more accurate
          • Katch-McArdle Formula - uses lean mass
          • (Original) Harris-Benedict Equation - height, weight and age
          • Cunningham Formula - uses lean mass
          • Mifflin St Jeor Equation - does not take into account body composition
        • direct or indirect calorimetry, handheld device


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