METABOLISM
Historical Perspective
Definitions
Methods
Factors affecting
Metabolic Rate
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)
Energy
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
Energy
Maintenance, growth,
reproduction, activity
Food/fuel is oxidized to form ATP
Aerobic metabolism:
Fuel + O2
CO2 + H2O + ATP + heat
Metabolic rate (MR, or E)
= energy metabolism/time
What does MR tell us?
1. Overall rate of all physiological activities
2. Resource needs
3. Rate of production of new tissue
How can we measure MR?
Aerobic metabolism:
Fuel + O2
CO2 + H2O + ATP + heat
Indirect measures
Direct measures
*
1. Direct measure of heat production
= “direct calorimetry”
Lavoisier & Laplace
79.9 cal melts 1 g ice
(335 Joules)
How can we measure MR?
Aerobic metabolism:
Fuel + O2
CO2 + H2O + ATP + heat
Indirect measures
Direct measures
*
2. Indirect measure of MR
food intake (fuel)
O2 consumption
CO2 production
X
metabolic water
Complete oxidation of 1 mol glucose:
Fuel + 6O2
(C6H12O6)
6CO2 + 6H2O + 2820 kJ
•Amount of energy ingested, O2 consumed, or CO2
produced is directly related to amount of heat produced
Measuring O2 consumption:
Closed system respirometry:
Volume = 1 L
1000 mls
Initial O2 = 21%
210 mls O2
Final O2 = 15%
(1 hour)
150 mls O2
E = 0.06 L O2 /hr
Measuring O2 consumption:
Open system respirometry (flow through):
Constantly measure O2 consumption
Respirometry: Open and Closed
Can be used to measure BOTH:
Oxygen consumption
Carbon Dioxide Production
2. Indirect measure of MR
food intake (fuel)
O2 consumption
CO2 production
X
metabolic water
Complete oxidation of 1 mol glucose:
Fuel + 6O2
(C6H12O6)
6CO2 + 6H2O + 2820 kJ
•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…
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
lipids
38.9
19.8
27.9
Proteins (urea)
17.6
18.7
23.3
Relatively constant, but not exact…
E = 0.06 L O2 /hr
Heat produced
per liter of O2
consumed (KJ/L)
carbohydrates
To convert to heat production:
1) Use appropriate conversion
factor (on left)
- possible if you know food source
21.1
lipids
19.8
Proteins (urea)
18.7
-OR-
2) Use a “representative”
conversion factor
- 20.2 KJ/L
Thre is a more complicated method, but you need to measure both O2
consumption and CO2 production (rare)
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!
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
O
H
18O
H
(Water)
H
3H
(Doubly-labeled water)
Doubly-labeled water
18O
H
3H
measure the “washout”
rates of 3H and 18O
Inject into animal
• 3H lost as body water
(urination, sweating, breathing…)
**Loss rate for
18O
• 18O is lost as water
and CO2
is steeper than for 3H
isotope in body
Doubly-labeled water
Initial sample
3H
Final sample
18O
time
Convert to estimates of CO2 production…
Doubly-labeled water
 inject a known quantity into animal
 let equilibrate, take blood sample
 release animal
 recapture, take 2nd blood sample
isotope in body
Initial sample
3H
Final sample
18O
time
3H
:
18O
Doubly-labeled water
18O
H
Is it accurate?
• Predicts CO2 production w/in 3-8%
Limitations?
• cost of analysis
• radioisotope use in field
3H
What factors affect an animal’s
metabolic rate?
1. Activity
What factors affect an animal’s
metabolic rate?
2. Digestion: “specific dynamic action”
= MR increase after a meal
Humans: 30%
Why?
•Amount
•Type
1.4 kJ meal
5.6 kJ meal
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?
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!
What factors affect an animal’s
metabolic rate?
Many animals lower MR well below resting levels
5. Hibernation, Estivation,Torpor
6. Endothermy vs. Ectothermy
Relatively high MR
Relatively low MR
6. Endothermy vs. Ectothermy
physiological correlates of
huge MR difference
1. Higher SA/V in lungs; complex, efficient heart
2. Mitochondrial membrane SA ~4-5X bigger
3. Greater enzyme activity
6. Endothermy vs. Ectothermy
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”
7. Temperature affects MR
endotherms
BMR
??
“tnz”
MR
Basal Metabolic Rate:
Animal must be:
-in TNZ
-resting
-fasting
temperature
Thermoneutral zone = range of temps within
which MR is unaffected by temp change
7. Temperature affects MR
ectotherms
“Standard Metabolic Rate”
Animal must be:
-fasting
-resting
* SMR is specific
to body temp
SMR
MR
temperature
7. Temperature affects MR
ectotherms
endotherms
“tnz”
BMR
SMR
MR
MR
temperature
temperature
BMR:
-in TNZ
-resting
-fasting
SMR:
-fasting
-resting
-temperature specific
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
METABOLISM
Historical Perspective
Definitions
Methods
Factors affecting
Metabolic Rate
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
RQ
carbohydrates
17.1
21.1
21.1
1.0
lipids
38.9
19.8
27.9
0.7
Proteins (urea)
17.6
18.7
23.3
0.8
What if you aren’t sure what animal ate?
“Respiratory Quotient” = Rate of CO2 production
Rate of O2 production