RESPECT OF SUPERVISORY STANDARDS
See the table of standards .
The compliance with supervisory standards can limit the risks.
V. THE RISKS INHERENT IN OUTDOOR PRACTICE
A. - RISKS DUE TO CLIMATE CONDITIONS
1. THERMOREGULATION
Man: a homeothermic organism
The human body is a homeothermic organism, which means that its body temperature is almost constant.
The basal (lowest resting) temperature of the human body is around 37.0 ° C, however this value varies depending on the environment, physical activity and time of day when the measurement was taken. taken.
Thus the normal body temperature is between 36.1 ° C and 37.8 ° C.
A) FACTORS INFLUENCE BODY TEMPERATURE
The heat exchanges that occur in an individual between his body and the environment are all considered by the laws of thermodynamics composed of two principles:
The first is that of the conservation of energies. It tells us that the chemical energy absorbed by our body during meals, if it is not expended during physical exertion or during the rise in temperature during physical exertion, will be transformed into energy reserve in the form of lipids.
The second principle tells us that heat always flows from an environment at a higher temperature to a cooler environment, which happens every day for the body in contact with its environment.
B) untitled-3-4.jpgTHE HYPOTHALAMUS: THE CENTER OF THERMOREGULATION
The hypothalamus is a small region located at the heart of our brain. It is like the thermostat of our body. Indeed, it is his responsibility to regulate the temperature of our body, so that it remains constantly around 37 ° C whatever our environment. This is the principle of thermoregulation. The hypothalamus is alerted by thermoreceptors, the Krause corpuscle which captures cold, and the Ruffini corpuscle which captures heat, located in the epidermis, via central receptors.
Two mechanisms will therefore balance out thanks to the role of the hypothalamus:
Heat production, known as thermogenesis
Heat loss, known as thermolysis
2. THERMOGENESIS
At rest, a lot of heat is created by the metabolism of certain organs, mainly the liver, brain, heart and some glands, but muscles produce a large part of this heat.
Only a small part (less than 25%) of the energy is used for the physiological function of muscle contraction. Everything else is dissipated as heat.
If the outside temperature is above 32 ° C, heat exchange by radiation (which warms the body thanks to the sun or clothes) and by convection (principle of energy transfer between the central zone (heart, lungs, kidneys) and the peripheral zone by blood circulation) constitute a gain of heat because the skin temperature is lower than the outside temperature.
This causes a slowing of the heart rate, but also a narrowing of the blood vessels (vasoconstriction) in the periphery in order to promote internal circulation provided by the parasympathetic nervous system. It also creates norepinephrine to boost metabolism.
Heat propagation modes
3. THERMOLYSIS
It is a physical phenomenon ensuring the propagation and loss of heat thanks to:
radiation (transport of heat in the form of infrared from a cold object to a warmer object without any contact)
conduction (transmission of heat from one body to another by contact, this heat transmission is different depending on the nature of the solid, the liquid, the surfaces in contact. For example, water is 24 times more conductive than water. air. Indeed the conductivity of water is 0.6 while that of air is 0.025)
convection (heat transfer by a moving body)
evaporation (conversion of a liquid into vapor, a mechanism for combating the increase in temperature)
Thermolysis causes an increase in peripheral circulation (vasodilation) and an acceleration of the heart rate thanks to the sympathetic nervous system.
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