Earlier, it was repeatedly emphasized that the health status of an individual, a group of people, a population, an ethnos should be assessed as inseparable from the surrounding environment (natural or social). If you narrow down to a purely medical perspective on this problem, you can be sure that from ancient times to the present day the leading figures of medicine and hygiene have tirelessly taught their followers of the need to analyze the relationship between the human health and environmental factors.
Just recently, two clear concepts have been used, namely - the internal and external environment. The internal environment, as I.P. Pavlov wrote, is an internal content that provides nervous and humoral regulation mechanisms. This is the living environment of the body, which is delimited from the external environment by the stratum corneum, the epithelium of the mucous membranes of the respiratory organs, the reproductive and digestive systems and the excretory glands, as well as the exteroand interoceptors and is a collection of tissues including liquid (blood, lymph and tissue fluid) washing the cells and intercellular structures. Ultimately, its main function is to ensure the homeo-stasis of the body through the nervous and humoral regulation mechanisms.
Along with the concept of «internal environment», another term is widely used - the «external environment». In the most generalized form, everything that is outside the internal environment is an external environment. The state of the environment is purely individual for each person.
Over the past few decades, the outlook on the environment as a factor in influencing human health has changed. In addition to this term, the concept of «environment» has been introduced (see fig. 1.1).