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Learning Objectives: To understand how oxygen consumption is
used as an index of metabolic rate
To be familiar with the variation in energy expenditure between species (related to life strategies)
To appreciate the extent to which energy expenditure is elevated by animal movement in the laboratory and field
Reading … http://biolpc22.york.ac.uk/303/
Schmidt-Nielsen, K (1997) Animal Physiology CUP
So what is the cost of living?
Living organisms need energy just to exist
Basal metabolic rate
First estimated by Lavoisier ~1790.
At equilibrium: rate of ATP hydrolysis = rate of ATP synthesis(but ATP hydrolysis levels difficult to measure!)
1 mole glucose
+
6 moles O2
36 moles ATP
Energy as ATP…
Although Lavoisier measured heat production, the possibilities include measuring:
heat
Metabolic rate Metabolic rate: rate at which an organism
uses energy
determine from heat produced work done food ingested oxygen consumed CO2 production ?
And CO2
Respiratory quotient
RQ = CO2 produced / O2 consumed
1 for carbohydrate 0.7 for fat
O2 consumption = energy consumption
1ml O2 = 5 cals = 20 Joules
For a 70 kg human:• 65 kg ATP/day• 350l O2/day • 70 W (one light bulb)• 7 million joules of energy/day
Cost of doing nothing??
Physiological food value
How long live on a Kitkat?
20 g so 2105/100*20 = 421 kJ 421*1000/70 /60 ≈ 100 min
Warning!
food is often labelled in cal when they mean kcal
12% for a Mars bar!
In terms of energy cost (O2 required/kg/h), what is the most expensive tissue in the human body?
[ and why ? ]
Oxygen consumption by pigeon tissue slices maintainedin saline
Tissue ml O2 consumed kg-1h-1
Kidney 41Liver 34Brain 23Heart 13Muscle 10
(metabolic rate of tissue slices = 70% of basal metabolic rateof intact animal)
Spending: 20% ion pumping; 20% protein synthesis and turnover
Summary so far oxygen consumption as proxy for energy
consumption
Getting bigger…
mass
met
abol
ic r
ate BMR = K * mass0.75
and bigger… 0.75 law is called Kleiber’s law
Homeotherms need more energy
Getting bigger requires more metabolism become more efficient
for a 10% increase in size, metabolic rate increase is 5.6%
Evolutionary drive to get bigger
why 0.75 ? If directly proportional
big animals overheat small animals need several cm of fur
if index were 2/3 would agree with
surface / volume ratio
Pumping matters… West suggested 0.75 was due to
fractal branching pulsatile blood flow
Summary so far oxygen consumption as proxy for energy
consumption basal metabolic rate increases with size
Now onto: effect of activity on metabolic rate
Another day at the office……
Cost of running
body mass, kg, log scale
speed of running, km/hr
total costnet cost
0.01 1000
10 0
Classic study by Dick Taylor on ponies, three gaits: walking,Trotting, galloping on a treadmill:Same gait: different speeds
Black boxes: preferred speed at each gait = minimal metabolic cost
In general:
Animals use uniform amounts of energy/distance coveredat all speeds.
i.e. walk or run from here to Heslington Hall, uses the same amount of energy, but running takes you there faster
Metabolic costs of running (kJ kg-1 km-1):
Larger animals more efficient than small; think evolution!Number of legs does not matter
Swimming flying graph
maximum MR when running is 10 x BMR
Flying v swimming v running
European Eel (Anguilla anguilla)
Migrates 6000miles from W. Europe to Sargasso sea to spawn
Swimming eels consume 23mg fat/kg/h
2kg eel (20% fat) swims at 43.2 km/day for 139 days
consumes 153g fat = 38% of stored fat
…….leaving 413g fat for egg production
Sprinting… Some species can ‘sprint’: running faster than
O2 can be supplied to the muscles How possible?
Red Fibres: ATP production by aerobic respiration, fuelled by O2 delivery via blood during exertion of moderate force for extended periods
White Fibres: ATP production independent of O2 (little blood supply) during exertion of strong force for short periods – build up lactate during exercise.
All muscles have mixture, but some have high ratios of white to red.
Red and white muscle fibres
Limits to power output <1sec 4500 W muscle output <2 min 1500 W anaerobic energy store
kettle
<2 hours 350 W oxygen transport All day 150W need to eat/sleep
2 light bulbs
Mars bars again… How far can you run on a Mars bar ?
Summary so far oxygen consumption as proxy for energy
consumption basal metabolic rate increases with size cost of movement
independent of speed up to 60x BMR transiently, 5x BMR for several hours
Now onto: Life in the field
How do you study metabolic rate in the field?
Back to the originalquestion:
What is the cost of livingand how do you measureit?
Double Labeled Water technique
Key Technique: Aim: to measure FMR (field metabolic rate)
over period of time Only works on air-dwelling animals
Inject animals with 2H218O (harmless heavy
isotopes) Later time point: blood sample and
quantify 2H and 18O
DLW - 2loss of water : carries away 2H and 18Oloss of CO2 : just carries 18O
How does 18O get from water to carbon dioxide ?carbonic anhydase (very high turnover)
CO2 + H2O H+ + H2CO3¯ [proton + bicarbonate]
difference between loss of 18O and 2H measures CO2 used in expirationSo how much extra energy does an
active bird use?
Using double labeled water technique:
Blue-tits breeding in evergreen oak woodlandsin south of France (new leaves in May) and Corsica (new leaves in June)
FMR---------BMR
Nagy, K. A. J Exp Biol 2005;208:1621-1625Index of 0.80
FMR ~3x BMR
Summary to end oxygen consumption as proxy for energy
consumption basal metabolic rate increases with size cost of movement
independent of speed up to 60x BMR transiently, 5x BMR for several hours
field studies FMR 3-6 x BMR
