1. METABOLISM Historical Perspective Definitions Methods
Factors affecting Metabolic Rate

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. Metabolic Rate = Total energy metabolized by an organism per unit time
Maintenance, growth, reproduction, activity
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. Fuel + O2 CO2 + H2O + ATP + heat
Energy
Maintenance, growth, reproduction, activity
Food/fuel is oxidized to form ATP
Aerobic metabolism:
Fuel + O CO2 + H2O + ATP + heat

5. Metabolic rate (MR, or E)
= energy metabolism/time
What does MR tell us?
Overall rate of all physiological activities
Resource needs
Rate of production of new tissue

6. How can we measure MR? Fuel + O2 CO2 + H2O + ATP + heat
Aerobic metabolism:
Direct measures *
Indirect measures

7. 1. Direct measure of heat production
= “direct calorimetry”
Lavoisier & Laplace
79.9 cal melts 1 g ice
(335 Joules)

8. How can we measure MR? Fuel + O2 CO2 + H2O + ATP + heat
Aerobic metabolism:
Direct measures *
Indirect measures

9. X 2. Indirect measure of MR Fuel + 6O2 6CO2 + 6H2O + 2820 kJ
food intake (fuel)
O2 consumption
CO2 production
metabolic water X
Complete oxidation of 1 mol glucose:
Fuel + 6O CO2 + 6H2O kJ
(C6H12O6)
Amount of energy ingested, O2 consumed, or CO2 produced is directly related to amount of heat produced

10. Measuring O2 consumption:
Closed system respirometry:
Volume = 1 L
Initial O2 = 21%
1000 mls
210 mls O2
Final O2 = 15%
150 mls O2
(1 hour)
E = 0.06 L O2 /hr

11. Measuring O2 consumption:
Open system respirometry (flow through):
Constantly measure O2 consumption

12. Can be used to measure BOTH: Carbon Dioxide Production
Respirometry: Open and Closed
Can be used to measure BOTH:
Oxygen consumption
Carbon Dioxide Production

13. X 2. Indirect measure of MR Fuel + 6O2 6CO2 + 6H2O + 2820 kJ
food intake (fuel)
O2 consumption
CO2 production
metabolic water X
Complete oxidation of 1 mol glucose:
Fuel + 6O CO2 + 6H2O kJ
(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…

14. BUT, heat production varies with foodstuff being oxidized…
HEAT PRODUCTION (KJ)
Per gram of food
Per liter of O2 consumed
Per liter of CO2 produced
carbohydrates
17.1
21.1
21.1
38.9
19.8
27.9
lipids
17.6
18.7
23.3
Proteins (urea)
Relatively constant, but not exact…

15. Heat produced per liter of O2 consumed (KJ/L)
E = 0.06 L O2 /hr
To convert to heat production:
Use appropriate conversion factor (on left)
- possible if you know food source
-OR-
2) Use a “representative” conversion factor
KJ/L
Heat produced per liter of O2 consumed (KJ/L)
Proteins (urea)
lipids
carbohydrates
21.1
19.8
18.7
Figure kJ from O2 example with mouse
Thre is a more complicated method, but you need to measure both O2 consumption and CO2 production (rare)

16. 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!

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

18. Doubly-labeled water 18O H 3H Inject into animal
measure the “washout” rates of 3H and 18O
18O H 3H
Inject into animal
How does an animal lose hydrogens or oxygens?
3H lost as body water (urination, sweating, breathing…)
18O is lost as water and CO2
**Loss rate for 18O is steeper than for 3H

19. Doubly-labeled water isotope in body time3H
Initial sample
18O
Final sample
Convert to estimates of CO2 production…

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

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

22. What factors affect an animal’s metabolic rate?
1. Activity

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

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

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

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

27. 6. Endothermy vs. Ectothermy
Relatively high MR
Relatively low MR

28. 6. 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

29. 6. Endothermy vs. Ectothermy

30. 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”

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

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

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

34. Metabolic Rate Summary
What is MR and how can you measure it?
Direct Colorimetry (heat production)
Food Consumption
Oxygen Consumption
Carbon Dioxide Production
Field metabolic rate
Factors affecting metabolic rate:
Activity
Digestion
Starvation
Reproductive Status
Hibernation, Estivation, Torpor
Endothermy vs. Ectothermy
Temperature

35. METABOLISM Historical Perspective Definitions Methods
Factors affecting Metabolic Rate

36. BUT, heat production varies with foodstuff being oxidized…
HEAT PRODUCTION (KJ)
Per gram of food
Per liter of CO2 produced
Per liter of O2 consumed
Proteins (urea)
lipids
carbohydrates
17.1
38.9
17.6
21.1
27.9
23.3
19.8
18.7 RQ
1.0
0.7
0.8
What if you aren’t sure what animal ate?
“Respiratory Quotient” = Rate of CO2 production
Rate of O2 production