The thermoregulatory centre normally maintains a set point of 37.5 ± 0.5 °C in most mammals.
However the set point can be altered in special circumstances:
• Fever. Chemicals called pyrogens released by white blood cells raise the set point of the
thermoregulatory centre causing the whole body temperature to increase by 2-3 °C. This
helps to kill bacteria, inhibits viruses, and explains why you shiver even though you are hot.
• Hibernation. Some mammals release hormones that reduce their set point to around 5°C
while they hibernate. This drastically reduces their metabolic rate and so conserves their
food reserves e.g. hedgehogs.
• Torpor. Bats and hummingbirds reduce their set point every day while they are inactive.
They have a high surface area/volume ratio, so this reduces heat loss.