Transcript Temperature Regulation

Temperature Regulation
The Reverend Dr. David CM Taylor
http://pcwww.liv.ac.uk/~dcmt/Tempreg.ppt
Why temperature regulation?
• (The 19th century experiences of
puerperal fever and the hospital as a
‘gateway to death’ are historical
reminders of advances made.) “Birth is
big for babies too - many
changes. …Keep Baby warm.” In the
postnatal ward, Mrs Cheung asks, “Can
I feed her? Why are you taking my
temperature? I’d like my
aromatherapy!”.
What we will cover
Triggered by elements in the case scenario we will
consider:
• Why we regulate temperature?
• What is meant by “normal” body temperature
• What mechanisms there are for regulating body
temperature (and the importance of behavioural
mechanisms.
• How babies are different from adults.
• How fever occurs.
Why?
• All organisms are limited by their ability to survive in
different temperatures
• Some, like reptiles and amphibia are poikilothermic
• Others like humans are homeothermic
How?
• The actual body temperature is a
consequence of the balance between the
amount of heat produced and the amount of
heat lost. The balance may be altered
• physiologically or
• behaviourally
Balance
Body
Skin
Environment
Basal metabolic rate
Muscle activity
Conduction
Shivering
Convection
Vasomotor
Radiation
Sweating
Evaporation
Piloerection
Core Temperature
So how is it regulated?
Reference
Set-point
hypothesis
Response
Feedback
Controlled
system
Balance hypothesis
Response
cool
warm
Feedback
Feedback
Controlled
system
Inputs
Outputs
Central
thermosensors
warm cool
Hypothalamus
Peripheral
thermosensors
warm cool
Neural
sweating
shivering
vasoconstriction
vasodilation
Hormonal
adrenaline
TRH
Babies
• Babies (and hamsters) have an
extra mechanism
• Brown fat.
• Suprascapular deposits
• Rich in mitochondria
Normal body temperature
• Depends where and when you
measure it
• tympanic> oral > axillary by 0.5oC
• can be affected by
• exercise
• emotion
• time of day
And the menstrual cycle (o- p+)
37.4
Postovulatory
Rectal
temp
OC
36.8
Preovulatory
36.2
12
18
24
6
Time
12
Fever
• monocytes and phagocytes release
endogenous pyrogen (Interleukin-1, IL-1).
• The anterior hypothalamus is sensitive to IL-1
• Hypothalamic sensitivity to temperature is
altered.
So…
• The body temperature then becomes
regulated at a new, higher level.
• There is some evidence that the raised
body temperature enables the fight
against the infection.
But...
• Every 1OC rise in temperature increases
basal metabolic rate and oxygen
consumption by about 13%,
• In acute infection, the ability to mobilise
fat stores is inhibited.
Consequently
• Skeletal muscle is broken down and the
amino acids are used in gluconeogenesis.
• This can be debilitating.
And even worse
• In addition to the increased demand for
energy
• Temperatures (above 42OC) damage
nerve cells
• impair thermoregulation
• have more serious consequences.