Temperature Regulation The Reverend Dr. David CM Taylor dcmt/Tempreg.ppt.

Temperature RegulationThe 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

Basal metabolic rate

Muscle activity

Shivering

Vasomotor

Sweating

Piloerection

Conduction

Convection

Radiation

Evaporation

Body Skin Environment

Balance

Core Temperature

Reference

Response

Controlled system

Feedback

Set-point Set-point hypothesishypothesis

So how is it regulated?

Response

Controlled system

Feedback

Balance hypothesisBalance hypothesis

Feedback

warmcool

Inputs Outputs

Hypothalamus

Central thermosensors

warm cool

Peripheral thermosensors

warm cool

Neuralsweatingshivering

vasoconstrictionvasodilation

Hormonaladrenaline

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

RectaltempOC

37.4

36.8

36.2

12 18 624 12Time

Postovulatory

Preovulatory

And the menstrual cycle (o- p+)

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.