METABOLISM Historical Perspective Definitions Methods Factors affecting Metabolic Rate
Dec 21, 2015
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 matterMetabolic Rate = Total energy metabolized by an organism per unit time
Fuel + O2 CO2 + H2O + ATP + heat
Aerobic metabolism:
Energy Maintenance, growth, reproduction, activity
Food/fuel is oxidized to form ATP
What does MR tell us?1. Overall rate of all physiological activities2. Resource needs3. Rate of production of new tissue
= energy metabolism/time
Metabolic rate (MR, or E)
How can we measure MR?
Indirect measures
Fuel + O2 CO2 + H2O + ATP + heat
Aerobic metabolism:
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?
Indirect measures
Fuel + O2 CO2 + H2O + ATP + heat
Aerobic metabolism:
Direct measures*
2. Indirect measure of MR
Complete oxidation of 1 mol glucose:
Fuel + 6O2 6CO2 + 6H2O + 2820 kJ
•Amount of energy ingested, O2 consumed, or CO2 produced is directly related to amount of heat produced
(C6H12O6
)
food intake (fuel)O2 consumptionCO2 production
metabolic waterX
Closed system respirometry:
Volume = 1 L
Initial O2 = 21%
E = 0.06 L O2 /hr
(1 hour)
Final O2 = 15%
Measuring O2 consumption:
210 mls O2
150 mls O2
1000 mls
Respirometry: Open and Closed
Can be used to measure BOTH:Oxygen consumption
Carbon Dioxide Production
2. Indirect measure of MR
Complete oxidation of 1 mol glucose:
Fuel + 6O2 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…
(C6H12O6
)
food intake (fuel)O2 consumptionCO2 production
metabolic waterX
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
21.1
19.8
18.7
BUT, heat production varies with foodstuff being oxidized…
Relatively constant, but not exact…
E = 0.06 L O2 /hr To convert to heat production:
1) Use appropriate conversion factor (on left)- possible if you know food source
-OR-
2) Use a “representative” conversion factor
- 20.2 KJ/L
Heat produced per liter of O2
consumed (KJ/L)
Proteins (urea)
lipids
carbohydrates 21.1
19.8
18.7
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?
Why?
Values of MR in field are 3X higher than in lab!!
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 H
(Water)
18O
H 3H
(Doubly-labeled water)
Doubly-labeled water
• 18O is lost as water and CO2
measure the “washout” rates of 3H and 18O
Inject into animal
• 3H lost as body water (urination, sweating, breathing…)
**Loss rate for 18O is steeper than for 3H
18O
H 3H
Doubly-labeled wateris
oto
pe in
body
time
18O
3HInitial sample
Final sample
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
3H : 18O
isoto
pe in b
ody
time
18O
3H
Initial sample
Final sample
Doubly-labeled water
Is it accurate?
Limitations?
• Predicts CO2 production w/in 3-8%
• cost of analysis• radioisotope use in field
18O
H 3H
What factors affect an animal’s metabolic rate?
2. Digestion: “specific dynamic action”
Humans: 30%
Why?1.4 kJ meal5.6 kJ meal
= MR increase after a meal
•Amount•Type
What factors affect an animal’s metabolic rate?
3. Starvation
Metabolic rate drops
Why might this be adaptive?
2. Digestion: “specific dynamic effect”
= MR increase after a meal
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
- lactation takes up 1/3 of yearly energy budget!
• Golden-mantled ground squirrels:
What factors affect an animal’s metabolic rate?
Many animals lower MR well below resting levels
5. Hibernation,Estivation,Torpor
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
thermoregulation
digestion
activity
basic metabolism
digestion
activity
reproduction/growth reproduction/growth
“Basal MR” “Standard MR”
7. Temperature affects MR
BMR“tnz”
Thermoneutral zone = range of temps within which MR is unaffected by temp change
MR
temperature
endotherms
-in TNZ-resting-fasting
Animal must be:
Basal Metabolic Rate:??
7. Temperature affects MR
SMR
MR
ectotherms
temperature
“Standard Metabolic Rate”
Animal must be:
-fasting-resting
* SMR is specific to body temp
7. Temperature affects MR
BMR“tnz” SMR
MR
ectotherms
temperature
MR
temperature
endotherms
-in TNZ-resting-fasting
BMR: 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
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
21.1
19.8
18.7
BUT, heat production varies with foodstuff being oxidized…
“Respiratory Quotient” = Rate of CO2 productionRate of O2 production
RQ
1.0
0.7
0.8
What if you aren’t sure what animal ate?