FLUID HEAT & METABOLISM
INTRODUCTION & OVERVIEW
Eamonn O’Connor
Trinity College Dublin
Objectives
1
To understand the interaction and regulation of 3 important
physiological systems:
  Thermoregulation (temperature)
  Metabolism
  Fluid balance (H2O)
 
Thermoregulation
Metabolism
H2O
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Problem
2
Which gets “hotter”?
  Different substances
  Same amount of heat
 
Why?
 
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Specific Heat
3
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
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Body Composition
4
In general for humans, mammals & animals
 
 
Approximately 70% water (H2O)
Important given thermal challenges
 
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Thermal Challenges
5
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Thermoregulation
6
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
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Homeotherms v Poikilotherms
7
 
 
 
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:
  Endothermic poikilotherms:
  Ectothermic homeotherms:
  Ectothermic poikilotherms:
  Heterotherms (hibernators):
humans
tuna
ground squirrels
insects, lizards
Bears
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Homeotherms v Poikilotherms
8
40
30
20
10
10
20
30
40
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Human Thermoregulation
9
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Regulation v Control
10
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
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Regulation v Control
11
C
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n
t
r
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l
l
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Regulation v Control
12
 
 
Often use negative feedback
Are represented as flow charts or equations
  For example: Blood osmolality OR Electrolyte conc.
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Regulation v Control
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 
For example: blood pressure regulation
  Pressure is stable around a point
  Fluctuates according to controlling variables
  Controlling variables influenced by neural input
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