The Phenomenon of Sweating: Diving into Science
February 12th, 2022
The Phenomenon of Sweating:
Diving into Science
What kind of fluid is it, that our body excretes? The principle is familiar to most people: we sweat during exercise, when we’re scared, in increased temperatures and when we’re nervous.
Now we’ll primarily concentrate on sweating during exercise. While training, a big amount of warmth is produced by the contracting muscles as a side product of the metabolism, which leads to an increase of temperature in the body. If the ambient temperature is higher than the skin temperature, warmth is being transmitted to the body.
The resulting increase in core body temperature is sensed by central skin thermoreceptors and this information is processed by the brain to activate sweating, or general temperature lowering measures. Evaporation of sweat is the primary pathway of heat loss during exercise. During sweating, heat is transferred from the body to water (sweat) on the surface of the skin. When this water gains sufficient heat, it is converted to water vapor, which removes heat from the body.
Sweat consists largely of water. In addition, there is a salt content, i.e. dissolved electrolytes such as sodium, chloride and potassium ions as well as other salts. It also contains various fatty acids, urea, amino acids, ammonia, lactic acid, ascorbic acid, cholesterol and sugar. However, these substances are now rather placed in the background - we are interested in the salts.
Sweat as thermoregulator
Fundamental to understanding the principle of thermoregulation is the information that the human body temperature remains largely independent of external temperature fluctuations. The human organism is therefore homoiothermic, i.e. equally warm. Various regulatory mechanisms have evolved to ensure that the body temperature remains the same under different conditions.
Mechanisms of heat dissipation are, for example, the following:
- Heat dissipation by conduction describes the transport of heat energy due to molecular processes. In this process, faster molecules from warmer regions transfer kinetic energy to regions of slower molecules that are colder.
- The transport of heat energy through flowing fluids (e.g. blood/breathing gases) describes convection. This occurs macroscopically and can therefore also transport energy in larger quantities.
- Thermal radiation describes the transfer of thermal energy by electromagnetic waves (e.g. infrared waves of sunlight).
- The last and probably best-known mechanism of heat dissipation is that of evaporation of water on the surface of the skin, i.e. sweating.
The evaporation of sweat on the skin surface can release an amount of energy or heat of 2400 kJ, or about 580 kcal per liter of sweat. Sweat is secreted either via sweat glands, i.e. glandular, or via the non-waterproof skin between the sweat glands (extra-glandular).
Our body has developed two ways of sweating - the eccrine and apocrine sweat glands. While the eccrine sweat glands are mainly concerned with cooling the skin, the apocrine glands take over olfactory communication between the sexes and are therefore colloquially also called scent glands. They do not form until puberty and are hormonally controlled.
The water molecules in the sweat droplet move at a thermally determined speed. Some are faster, i.e. more energetic and thus warmer, while others are slower, i.e. less energetic and thus colder. The faster molecules near the surface manage to get out of the gas space into the surrounding air - they "evaporate". The slower ones remain behind and the temperature of the sweat drop drops.