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.