Fluids Heat and Metabolism
Introduction & Overview
Mikel Egaña
Trinity College Dublin
2012-13
Objectives
• To understand the interaction and regulation of 3
important physiological systems:
• 
Thermoregulation (temperature)
• 
Metabolism
• 
Fluid balance (H2O)
Thermoregulation
Metabolism
H2O
Fluids Heat and Metabolism.
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Problem
• Which gets “hotter”?
• 
Different substances
• 
Same amount of heat
• Why?
Fluids Heat and Metabolism.
Specific Heat
The amount of heat per unit mass required to raise the
temperature by one degree Celsius (°C)
Substance
Specific Heat (J/gm)
Aluminium
0.90
Gold
0.13
Granite
0.79
Glass
0.84
Ethanol
2.40
Ice
2.05
Water
4.19
Fluids Heat and Metabolism.
2
Body Composition
• In general for humans, mammals & animals
• 
Approximately 70% water (H2O)
• Important given thermal challenges
Fluids Heat and Metabolism
Thermal Challenges
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Thermoregulation
The homeostatic ability to regulate internal core
body temperature to a predetermined
physiological level enabling proper function in
environments with temperatures ranging from
hot to cold
Fluids Heat and Metabolism
Homeotherms v Poikilotherms
• HOMEOTHERMS: THERMOREGULATION
• 
Warm blooded vertebrates: Mammals (humans) & birds
• 
Endothermic: can produce own heat internally via oxidative
metabolism
• POIKILOTHERMS: NO THERMOREGULATION
• 
Cold blooded vertebrates: Reptiles, amphibians, insects & fish
• 
Ectothermic: obtains heat via it’s external environment
• Combinations:
• 
Endothermic homeotherms:
humans
• 
Endothermic poikilotherms:
tuna
• 
Ectothermic homeotherms:
ground squirrels
• 
Ectothermic poikilotherms:
insects, lizards
• 
Heterotherms (hibernators):
Bears
Fluids Heat and Metabolism
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Homeotherms v Poikilotherms
40
30
20
10
10
20
30
40
Fluids Heat and Metabolism
Human Thermoregulation
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Regulation v Control
• Regulated variable:
•  Variables with tensive (tight) fluctuations which
average out around a particular regulated point
•  Generally always involve sensors
• Controlled (modulated) variable:
•  Variables (often organ functions) with wide variations
which result in relative stability of regulated
variables
•  Often varied via neural input
Fluids Heat and Metabolism
Regulation v Control
C
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n
t
r
o
l
l
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r
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Regulation v Control
•  Often use negative feedback
•  Are represented as flow charts or equations
•  For example: Blood osmolality OR Electrolyte conc.
Fluids Heat and Metabolism
Regulation v Control
• For example: blood pressure regulation
• 
Pressure is stable around a point
• 
Fluctuates according to controlling variables
• 
Controlling variables influenced by neural input
Fluids Heat and Metabolism
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