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METABOLISM

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  1. METABOLISM Factors affecting Metabolic Rate Definitions Methods

  2. Antoine Lavoisier, 1773 • heat produced by an animal is proportional to O2 consumed and CO2 produced • so…“animal heat” is a byproduct of chemical reactions (metabolism)

  3. Maintenance, growth, reproduction, activity Energy Food/fuel is oxidized to form ATP Metabolism= sum of all biological transformations of energy and matter Metabolic Rate= Total energy metabolized by an organism per unit time

  4. Relatively high MR Relatively low MR What factors affect an animal’s metabolic rate? 1. Endothermy vs. Ectothermy

  5. 1. Endothermy vs. Ectothermy • physiological correlates of huge MR difference • Higher SA/V in lungs; complex, efficient heart • Mitochondrial membrane SA ~4-5X bigger • Greater enzyme activity

  6. 1. Endothermy vs. Ectothermy

  7. endotherms ?? MR BMR temperature 2. Temperature affects MR Basal Metabolic Rate: Animal must be: “tnz” -in TNZ -resting -fasting Thermoneutral zone = range of temps within which MR is unaffected by temp change

  8. ectotherms MR temperature 2. Temperature affects MR “Standard Metabolic Rate” Animal must be: SMR -fasting -resting * SMR is specific to body temp

  9. ectotherms endotherms MR MR BMR temperature temperature 2. Temperature affects MR “tnz” SMR -in TNZ -resting -fasting -fasting -resting -temperature specific BMR: SMR:

  10. 3. Hibernation, Estivation Torpor What factors affect an animal’s metabolic rate? Many animals lower MR well below resting levels

  11. 3. Hibernation/torpor

  12. Body Temperature Daytime temp Time of day Significantly lowered Tb 3. Hibernation/torpor

  13. 4. Activity What factors affect an animal’s metabolic rate?

  14. Golden-mantled ground squirrels: What factors affect an animal’s metabolic rate? 5. Reproductive Status • Humans:MR increases 30% near term -growth of fetus -fetal metabolic requirements -growth of mammary tissue - lactation takes up 1/3 of yearly energy budget!

  15. Humans: 30% 1.4 kJ meal 5.6 kJ meal What factors affect an animal’s metabolic rate? 6. Digestion: “specific dynamic action” = MR increase after a meal • Amount • Type Why?

  16. What factors affect an animal’s metabolic rate? 6. Digestion: “specific dynamic effect” = MR increase after a meal 7. Starvation Metabolic rate drops Why might this be adaptive?

  17. Factors affecting metabolic rate • Endothermy vs Ectothermy • Temperature • Hibernation, torpor, estivation • Activity • Reproductive Status • Digestion • Starvation

  18. What does measuring O2 consumption tell us? Endotherms: Ectotherms: • basic metabolism • basic metabolism • thermoregulation • digestion • digestion • activity • activity • reproduction/growth • reproduction/growth “Basal MR” “Standard MR”

  19. METABOLISM Factors affecting Metabolic Rate Definitions—levels of metabolism Methods

  20. Maintenance, growth, reproduction, activity Energy Fuel + O2 CO2 + H2O + ATP + heat Food/fuel is oxidized to form ATP Aerobic metabolism:

  21. Metabolic rate (MR, or E) Fuel + O2 CO2 + H2O + ATP + heat = energy metabolism/time What does MR tell us? • Overall rate of all physiological activities • Resource needs • Rate of production of new tissue How can we measure it? Aerobic metabolism:

  22. Fuel + 6O2 6CO2 + 6H2O + 2820 kJ Measuring MR O2 consumption CO2 production food intake (fuel) + + H2O + ATP + heat Complete oxidation of 1 mol glucose: (C6H12O6) glucose • Amount of energy ingested, O2 consumed, or CO2 produced is directly related to amount of heat produced

  23. Lavoisier & Laplace 79.9 cal melts 1 g ice (335 Joules) Measuring MR O2 consumption CO2 production food intake (fuel) + + H2O + ATP + heat = “direct calorimetry”

  24. E = 0.06 L O2 /hr Measuring MR O2 consumption CO2 production food intake (fuel) + + H2O + ATP + heat Closed system respirometry: Volume = 1 L Initial O2 = 21% 1000 mls 210 mls O2 Final O2 = 15% 150 mls O2 (1 hour)

  25. Measuring MR O2 consumption CO2 production food intake (fuel) + + H2O + ATP + heat Open system respirometry (flow through): Constantly measure O2 consumption

  26. Measuring MR O2 consumption CO2 production food intake (fuel) + + H2O + ATP + heat Respirometry: Open and Closed Can be used to measure BOTH: Oxygen consumption Carbon Dioxide Production

  27. Fuel + 6O2 6CO2 + 6H2O + 2820 kJ Measuring MR O2 consumption CO2 production food intake (fuel) + + H2O + ATP + heat Complete oxidation of 1 mol glucose: (C6H12O6) • Amount of energy ingested, O2 consumed, or CO2 produced is directly related to amount of heat produced • BUT, heat production varies with foodstuff being oxidized…

  28. Relatively constant, but not exact… E = 0.06 L O2 /hr Measuring MR O2 consumption CO2 production food intake (fuel) + + H2O + ATP + heat BUT, heat production varies with foodstuff being oxidized… HEAT PRODUCTION (kJ) Mouse: Per gram of food Per liter of O2 consumed 0.06L O2 x 21.1 = 1.27 kJ 21.1 17.1 carbohydrates kJ?: 19.8 38.9 lipids 18.7 0.06L O2 x 18.7 = 1.12 kJ 17.6 kJ?: Proteins

  29. How does energy use compare between lab and field? • Values of MR in field are 3X higher than in lab!! Why? Field metabolic rate, (“FMR”) accounts for activity levels!

  30. 18O O H 3H H H (Water) (Doubly-labeled water) How can we measure FMR? Doubly labeled water: • dual isotope technique • can use with free-ranging terrestrial animals • no equipment attached to animal • measures CO2 production

  31. Inject into animal Doubly-labeled water measure the “washout” rates of 3H and 18O 18O H 3H • 3Hlost as body water (urination, sweating, breathing…) • 18Ois lost as water and CO2 **Loss rate for 18O is steeper than for 3H

  32. Initial sample 3H isotope in body Final sample 18O time Doubly-labeled water Convert to estimates of CO2 production…

  33. 3H Initial sample Final sample isotope in body 18O time Doubly-labeled water • inject a known quantity into animal • let equilibrate, take blood sample • release animal • recapture, take 2nd blood sample 3H : 18O

  34. 18O H 3H Doubly-labeled water Is it accurate? • Predicts CO2 production w/in 3-8% Limitations? • cost of analysis • radioisotope use in field

  35. Metabolic Rate Summary • Factors affecting metabolic rate: • Endothermy vs. Ectothermy • Temperature • Hibernation, Estivation, Torpor • Activity • Reproductive Status • Digestion • Starvation • Levels of Metabolism • BMR, SMR, RMR, FMR, PMR, metabolic scope • What is MR and how can you measure it? • Direct Colorimetry (heat production) • Food Consumption • Oxygen Consumption • Carbon Dioxide Production • Field metabolic rate O2 consumption CO2 production food intake (fuel) + + H2O + ATP + heat