Human Adaptations to Environmental Changes
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Human adapts to environmental changes differently according to their individual capabilities.
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Human Adaptations to Environmental Changes
- 1. HUMAN ADAPTATIONS TO ENVIRONMENTAL CHANGES GARRY D. LASAGA Reporter
- 3. Adaptation Survival response to a change in the environment. Changes or adjustments in the structure or habits of an individual that improve its condition in relationship to its environment. Fundamental to survival and prosperity. Tipton et al., 1986
- 4. Environmental Stressors Heat Cold Dehydration Altitude Noise
- 5. Stress-Strain STRESS A threat to homeostasis from the external or internal environment. STRAIN The physiological response of the organism.
- 6. HUMAN ADAPTATIONS TO THERMAL STRESS
- 8. BODY TEMPRATURE Core (Tc) Shell (Ts) Folk et al., 1998; Gisolfi & Mora, 2000
- 9. Core temperature • Endothermic, brain Shell temperature • Ectothermic, external environment & skin blood flow Gisolfi & Mora, 2000
- 12. REGULATION OF BODY TEMP. Physiological Heat stress Behavioral Cold stress Sawka et al., 2001
- 14. HEAT ACCLIMATION Adaptations that mitigate physiological strain of heat stress. Induced by repeated heat exposures that are sufficiently stressful to elevate core & skin temperatures and elicit perfuse sweating.
- 15. Heat Stress Results from the interaction of environmental conditions*, physical work rate* and wearing of heavy clothing/equipment that impedes heat loss (Sawka et al., 2001). STRAIN – manifested by high skin & core temp., excessive cardiovascular strain & reduced performance (negative effects).
- 16. How does an individual become acclimated to heat? One becomes acclimated to the heat through repeated exposures that are sufficiently stressful to elevate both core & skin temperatures & provide profuse sweating (Sawka et al., 2001).
- 17. Heat acclimation Thermal comfort Core temperature Sweating Blood flow Metabolic rate Exercise performance Cardiovascular stability Fluid balance
- 18. HEAT ADAPTATIONS Lower core temperat ure Improved sweating & skin blood flow Lower metabolic rate Reduced cardiovas cular strain Improved fluid balance Increased thermal tolerance
- 19. ADAPTATIONS TO COLD STRESS Habituation Metabolic adaptations Insulative adaptations
- 20. Habituation Characterized by blunted shivering, blunted cutaneous vasoconstriction, or both; Body temperature may decline more in the acclimatized than unacclimatized state. Most common cold adaptation and results from periodic short-term cold exposures.
- 21. Metabolic Adaptations Characterized by enhanced thermogenesis that develops when cold exposures are more pronounced, but not severe enough to induce significant declines in core temperature. Example: metabolic cold adaptation by Alacaluf people (Hammel et al., 1964)
- 22. Insulative Adaptations Characterized by enhanced vasoconstriction and redistribution of body heat toward the shell. Develops from repeated cold exposures severe enough to induce marked declines in core temperature.
- 23. Insulative Adaptations Example: ABORIGINES living in the central Australian desert (Hammel et al., 1959; Scholander et al. 1958; Hilton, 1977;) Nomadic, lived out of doors, wore no clothing.
- 24. 1847 Warumunga men, Tennant Creek ca. 1895
- 25. Insulative Adaptations The Aborigines had a greater fall in skin temperature than the Europeans (circumpolar residents) – more pronounced cutaneous vasoconstrictor response.
- 26. ADAPTATIONS TO COLD STRESS Habituation Metabolic adaptations Insulative adaptations
- 27. Main Reference Sawka, M. N., J. W. Catellani, K. B. Pandolf, and A. J. Young. 2001. Human Adaptations to Heat and Cold Stress. Paper presented at the RTO HFM Symposium on "Blowing Hot and Cold: Protecting Against Climatic Extremes held in Dresden, Germany, 8-10 October 2001, and published in RTO-MP-076.
- 28. Main Reference Tipton, M. J., K. B. Pandolf, M. N. Sawka, J. Werner, and N. A. S. Taylor. 2008. Physiological adaptation to hot and cold environments. https://www.researchgate.net/publication/2710147 66 (Accessed 28 January 2018)
Editor's Notes
- It is a fact that the environment is the major factor that has influenced and determined the evolution of humans for 3-4 million years. The colonisation of the planet from man’s origins as a tropical animal of the African or Asian plains was largely complete by 30,000– 15,000 bc. The migrations from one area to the other were dependent on the ability to adapt to the environmental extremes experienced by humans. Thus, for millions of years, humans have survived the extremes of the environment through adaptation.
- ADAPTATION is defined as changes or adjustments, often hereditary, in the structure or habits of a species or individual that improve its condition in relationship to its environment. Adaptation can influence all the systems and states of a living organism and, in so doing, is fundamental to survival and prosperity. In addition, we adapt to the changes in the environment in order for us to maintain homeostasis or the state of stability of the internal environment of the body. There are various changes in the environment that we face in our daily lives, and when it poses a threat to homeostasis, we refer to them stressors.
- Others are hypoxia, malnutrition, radiation, pollution and others. This report will focus on how human adapts to hot and cold environments and the integrated physiological responses that accompany these adaptations. Before we discuss the human adaptation to cold and heat, we first define the common terminologies that we’ll be using in the discussion.
- STRESS examples: External – temperature, pressure, hypoxia; Internal – disease STRAIN examples: altered metabolic rate, redistribution of blood flow
- Humans encounter thermal (heat & cold) stress from climatic conditions, insulation worn and body heat production. Alterations in body temperature above and below normal levels can degrade exercise performance and cause thermal injury. Most importantly, it can be detrimental to cellular & organ functions, which can threaten survival of the host.
- In humans, body temperature comprises the temperature of the core and shell. The core temperature refers to the temperatures of the abdominal, thoracic and cranial cavities. The shell temperature refers to the temperatures of the skin, subcutaneous tissue and muscles.
- In terms of the REGULATION, Tc is regulated by the brain, whereas Ts is influenced more by skin blood flow and environmental conditions. Tc, because it is regulated by the brain is endothermic while Ts, because it is being influenced by the external environment, is ectothermic. This may imply that, when we are going to be exposed in an environment having a cold ambient temperature, it can decrease our Ts, but our Tc may remain relatively constant.
- We said that the Ts is mainly influenced by the external environment particularly the ambient temperature. Hence, during heat stress, there is an elevated Ts; upon exposure to heat stress, the blood flow in the skin has increased resulting in the elevated Ts and an increase in heat dissipation to the environment. In contrast, cold stress reduces the Ts. This is because cold stress reduces the blood flow to the skin, leading to decrease in Ts and conservation of heat in the body.
- The Tc is much more important because fluctuations can have significant implications on homeostasis in the body because it reflects the amount of heat in the circulation and the cells and organs in the abdominal, thoracic and cranial cavities. Extremes in Tc (˃42°C) can be detrimental to cellular and organ functions, which can threaten survival of the host. HYPERTHERMIA – can impair the CNS and cause systemic inflammation, tissue necrosis and multiple organ failures. HYPOTHERMIA – impairs cardiovascular, respiratory and CNS functions, which can lead to muscle damage, pulmonary edema, hypotension, bradycardia, and renal failure.
- Humans regulate core temperature within a narrow range (35° to 41°C) through two parallel processes: physiological and behavioral temperature. Physiological temperature regulation operates through responses that are independent of conscious voluntary behavior, and includes control of: a) rate of metabolic heat production, b) body heat distribution via the blood from the core to the skin, and c) sweating. Behavioral temperature regulation operates through conscious behavior, and includes actions such as modifying activity levels, changing clothes and seeking shelter. For humans, physiological thermoregulation is most important during heat stress and behavioral thermoregulation is most important during cold stress.
- ACCLIMATIZATION – adaptations that occur over a period of days to months in response to a change in the natural environment. Usually there are more than one stressor in a natural environment. Ex.: – Desert: hot and dry – Altitude: cold and hypoxia – Spaceflight: microgravity, radiation, psychological ACCLIMATION - develops from experimental exposure to artificial conditions, usually one specific stressor is induced. – heat chamber – altitude chamber ACCOMOMODATION –adaptations that occur in a single cell or tissue to an environmental change – increased size of sweat glands: heat; decreased sensitivity of peripheral blood vessels to vasoconstriction: cold; increased muscle mass: exercise; decreased sensitivity of chemoreceptors: hypoxia; dark skin—tanning booth • Changes associated with acclimation HABITUATION - A reduction in response to an environmental stimulus over time – less vasoconstriction in the hands with repeated cold water immersion – less increase in heart rate with repeated heat exposure • Responses are often a sign of acclimation
- Heat acclimation consists of adaptations that mitigate physiological strain of heat stress, which improve thermal comfort and exercise capabilities. Adaptations are induced by repeated heat exposures that are sufficiently stressful to elevate core and skin temperatures and elicit perfuse sweating. Most adaptations to daily heat exposure occur during the first four days, and the remainders are complete by three weeks.
- *ENVIRONMENTAL CONDITIONS: temperature, humidity, sun/*PHYSICAL WORK RATE: body heat production Environmental heat stress & exercise interact synergistically to increase strain on physiological systems. This strain is manifested by high skin temperatures, excessive cardiovascular strain and reduced performance. HEAT ACCLIMATION – results in biological adaptations that reduce these negative effects of heat stress.
- *ENVIRONMENTAL CONDITIONS: temperature, humidity, sun/*PHYSICAL WORK RATE: body heat production Environmental heat stress & exercise interact synergistically to increase strain on physiological systems. This strain is manifested by high skin temperatures, excessive cardiovascular strain and reduced performance.
- The effects of heat acclimation can be grouped into 2: the first is the effect on thermal comfort and the other on the exercise performance. This effects are in reference to heat acclimated vs unacclimated subjects. Heat acclimation will improve the parameters of heat comfort and it will also improve the exercise performance parameters. The CORE TEMPERATURE will be REDUCED. SWEATING PARAMETERS will be improved. After acclimation, sweating starts earlier and at a lower core temperature, i.e., the core temperature threshold for sweating is decreased. Sweating rate is increased. Earlier and greater sweating improves evaporative cooling and reduces body heat storage and skin temperature. The BLOOD FLOW is generally increased. After heat acclimation, the METABOLIC RATE is LOWERED. The CARDIOVASCULAR STABILITY after heat acclimation is generally improved. Under this, the heart rate of a person after the 2nd day of exercise is lowered. There is an increased stroke volume because of increased blood flow and the blood pressure is better compared with the control. The FLUID BALANCE is improved. The first parameter under this is thirst. Thirst is reduced because heat acclimated persons will dehydrate less during exercise in the heat, provided that access to fluids is not restricted. There is a REDUCTION IN ELECTROLYTE LOSS, particularly sweat sodium losses. An unacclimatized person can lose large amounts of sodium in sweat during exercise as compared to heat acclimatized individuals who only loses a very minimal amount of sodium in sweat. Hence, heat acclimation has salt-conserving effect that is due to aldosterone secretion of the adrenal cortex in response to exercise and heat. There is also an INCREASE IN PLASMA VOLUME and TOTAL BODY WATER which can be attributed to the increased aldosterone secretion.
- Heat acclimation mediated adaptations include: lower core temperature, improved sweating and skin blood flow, lowered metabolic rate, reduced cardiovascular strain, improved fluid balance, and increased thermal tolerance (i.e., cellular stress protein adaptations; HSP). When a heat acclimated person is performing exercise, there is an improved submaximal exercise response because of reduction in physiologic strain. There are 3 classical signs of heat acclimation: LOWER HEART RATE & CORE TEMPERATURE, and HIGHER SWEAT RATE during exercise-heat stress.
- *Adaptations to chronic cold exposure can be categorized into three patterns: habituation, metabolic adaptations and insulative adaptations. The magnitude and extent of body cooling, frequency and duration of exposure, and individual factors all influence the adaptive process. HABITUATION – characterized by blunted shivering, blunted cutaneous vasoconstriction, or both; body temperature may decline more in the acclimatized than unacclimatized state. It is the most common cold adaptation and results from periodic short-term cold exposures. METABOLIC ADAPTATIONS -
- * **Habituation appears to require only brief, intermittent cold exposures to be induced, and can develop when only small body regions are exposed unprotected to cold. It allows extremity skin temperatures to be maintained higher during cold exposure. The higher skin temperatures coupled with the absence of shivering are advantageous in that manual dexterity and comfort are enhanced. Thermogenesis – production of heat, esp within the animal body. Shivering thermogenesis - resulting from increase metabolism of the skeletal muscles due to shivering. Non-shivering thermogenesis – increased heat production due to enhancement of normal calorigenic metabolic process. Habituation is exemplified by a study where cold-exposed circumpolar residents (Inuits, North American natives, Norwegian Lapps) where compared with control or unacclimatized subjects n terms of cold adaptation. The normal response to whole-body cold exposure for both subjects are increase in metabolic heat production due to shivering & decrease in convective and convective heat loss decreases due to vasoconstriction of peripheral blood vessels.
- ****In one acclimation study in which subjects were exposed to moderate cold conditions C-, for a prolonged period, a metabolic form of cold acclimation appeared to develop. This adapta- C tion was characterized by an enhanced shivering thermogenesis during cold exposure. Thermogenesis – production of heat, esp within the animal body. Shivering thermogenesis - resulting from increase metabolism of the skeletal muscles due to shivering. Non-shivering thermogenesis – increased heat production due to enhancement of normal calorigenic metabolic process. An example of metabolic adaptation is exemplified by the Alacaluf people, who are nomadic Native Americans and lived on the tip of South America, where the climate was rainy and cool (lows from 0-8°C and highs from 5-15°C). The clothing and shelter of these people were less protective since there clothing is also made of loin cloth and cloth and their shelter from lean-tos built from scrap lumber. During a standardized overnight cold exposure, it was observed that the metabolic heat production was initially higher in Alacaluf than unacclimatized subjects. This was considered by researchers as evidence of enhanced thermogenesis or metabolic acclimatization, induced by chronic cold.
- When individuals acclimatize or acclimate to cold conditions severe enough to repeatedly cause a significantly body temperature fall, an insulative pattern of adaptation develops, characterized by < Z enhanced mechanisms for body heat conservation.
- The central Australian desert had a night-time lows of 0°C in winter and 20° in summer. In terms of their way of living, these people were nomadic who lived out of doors and wore no clothing. They slept on bare ground and their only protection from cold was a small fire at their feet and windbreak made from light brush.
- In contrast to habituated circumpolar residents, the Aborigines exhibited a greater fall in skin temperature than did Europeans which was attributed due to a more pronounced cutaneous vasoconstrictor response to cold (36,89). Additionally, the Aborigine's rectal temperature also fell more than in control subjects (31).
- * The mechanisms determining the pattern of adaptation to chronic cold exposure appear related to type of cold exposure conditions, the amount of body heat lost and the degree to which shivering thermogenesis compensates for Cy heat loss and defends body temperature.