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Sufficient stress from extreme external temperature may cause injury or death if it exceeds the ability of the body to thermoregulate. Hypothermia can set in when the core temperature drops to 35 °C (95 °F). [2] Hyperthermia can set in when the core body temperature rises above 37.5–38.3 °C (99.5–100.9 °F).
Simplified control circuit of human thermoregulation. [8]The core temperature of a human is regulated and stabilized primarily by the hypothalamus, a region of the brain linking the endocrine system to the nervous system, [9] and more specifically by the anterior hypothalamic nucleus and the adjacent preoptic area regions of the hypothalamus.
A 2022 study on the effect of heat on young people found that the critical wet-bulb temperature at which heat stress can no longer be compensated, T wb,crit, in young, healthy adults performing tasks at modest metabolic rates mimicking basic activities of daily life was much lower than the 35°C usually assumed, at about 30.55°C in 36–40°C ...
The shiver response may be greatly diminished or even absent in the elderly, resulting in a significant drop in mean deep body temperature upon exposure to cold. Standard tests of thermoregulatory function show a markedly different rate of decline of thermoregulatory processes in different individuals with ageing. [4]
Cooling results in a decrease in warm receptor discharge rate. For cold receptors their firing rate increases during cooling and decreases during warming. Some cold receptors also respond with a brief action potential discharge to high temperatures, i.e. typically above 45 °C, and this is known as a paradoxical response to heat [citation ...
In haemodynamics, the body must respond to physical activities, external temperature, and other factors by homeostatically adjusting its blood flow to deliver nutrients such as oxygen and glucose to stressed tissues and allow them to function. Haemodynamic response (HR) allows the rapid delivery of blood to active neuronal tissues. The brain ...
When stated in terms of temperature differences, Newton's law (with several further simplifying assumptions, such as a low Biot number and a temperature-independent heat capacity) results in a simple differential equation expressing temperature-difference as a function of time. The solution to that equation describes an exponential decrease of ...
As physical work is performed, the body's natural thermoregulation (i.e. sweating) becomes ineffective. This is compounded by increased work rates, high ambient temperature and humidity levels, and direct exposure to the sun. The net effect is that desired protection from some environmental threats inadvertently increases the threat of heat stress.