MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedoniuk 2010

BIOLOGY

CHAPTER 2. BIOGEOCOENOTIC LEVEL OF LIFE ORGANIZATION AND HUMAN PLACE IN IT

2.1. BASICS OF HUMAN ECOLOGY

Human adaptation to extreme conditions and the concept of stress

Social adaptation forms the foundation of human ADAPTATION TO ENVIRONMENTAL conditions. However, a vital role also belongs to biological adaptations, which depend on the functional state of defense mechanisms. These adaptations are particularly pronounced under extreme conditions—both natural (such as the Arctic or high-altitude regions) and artificial, including large cities affected by air pollution, noise, vibration, and high population density. For instance, individuals who relocate from the temperate zone to work in the Polar region often experience prolonged malaise, which is exacerbated by shifts in the polar day and night. These symptoms manifest as elevated Blood pressure and an accelerated pulse, followed by a subsequent drop in blood pressure, sometimes plunging to 70/30 mm Hg. Such physiological disruptions lead to decreased working capacity. Over time, functional parameters normalize in some individuals, while remaining altered in others; however, working capacity and well-being eventually recover, indicating that acclimatization to the new environment has occurred. The restoration of a high level of performance serves as the primary criterion for human acclimatization.

Human adaptation to extreme conditions can take the form of stress. The pioneering theory of stress proposed by the Canadian scientist Hans Selye is widely known (p. 237). Stress is a complex of adaptive bodily reactions aimed at overcoming the harmful effects of extreme factors and temporarily enhancing non-specific resistance. The factors triggering stress can vary widely: muscular and nervous overstrain, emotional excitement, trauma, infection, or abrupt environmental changes. While each of these factors elicits a specific response, they also trigger a non-specific, stereotyped reaction in the form of stress. General stress develops through three distinct stages: 1) the alarm stage, marked by the mobilization of the body's physiological reserves; 2) the stage of increased resistance; and 3) the stage of exhaustion of the body's defense mechanisms.

During the first stage—the alarm stage—receptor irritation occurs, activating the sympathoadrenal system and increasing the release of adrenaline by The adrenal medulla. This immediately exerts a profound effect on the body: blood sugar levels rise, Heart contractions intensify, and blood pressure increases. All of this enhances motor activity and overall functional readiness. In the second stage—the stage of increased resistance—adrenaline, acting via the Hypothalamus, stimulates specialized Cells to produce a neurohormone (liberin). This neurohormone acts on the anterior Pituitary Gland, which releases adrenocorticotropic hormone (ACTH) and stimulates The production of Adrenal Cortex Hormones that enhance the body's resistance to stressors: metabolic processes are activated, fat is mobilized from adipose depots, and blood levels of Amino Acids and glucose increase. The Third Stage—exhaustion—occurs upon exposure to an intense stressor, prolonged exposure to a mild stressor, or due to insufficient adaptive defense mechanisms. At this point, physiological strain becomes so severe that, despite hypertrophy, the adrenal cortex can no longer produce the required amount of hormones, causing the stress response to become pathogenic and leading to a breakdown of Homeostasis.