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 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

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

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?

1. Activity

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

6. Endothermy vs. Ectothermy

Relatively high MR Relatively low MR

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

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

METABOLISM

Historical Perspective

Definitions

Methods

Factors affecting Metabolic Rate

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?