A person has been sitting in a very cold room for an extended period of time. Their core body temperature begins to fall below the normal set point. Explain how the body detects this change and the responses that help to return body temperature to the set point.

Thermoreceptors in the skin and in the hypothalamus sense the drop in core temperature. The hypothalamus, acting as the thermostat, compares the measured temperature with the set point and, recognising a deficit, sends a signal via the autonomic nervous system to effectors. Two main responses are triggered:
1. Shivering – skeletal muscles contract rapidly, producing heat through increased metabolic activity.
2. Vasoconstriction – arterioles close to the skin narrow, reducing blood flow to the surface and limiting heat loss.
These mechanisms raise the core temperature back to the set point, restoring the internal environment to a normal, constant state.