Survival and Adaptation Survival “Niches”

Survival and Adaptation Survival “niches”

• How much of the Earth is inhabitable? – 2/3 of the Earth is ocean – 1/3 is land • 1/4 is permanently frozen • 1/4 is arid desert • high mts, lakes and rivers • Only about 1/6 of the Earth allows 1926 Byrd and Bennett: first to fly over permanent habitation the North Pole?

“Limit Physiology” Homeostasis Concept • Humans are among the most adaptable animals to their environment • Claude Bernard (late 1800s) – body fluids form an internal environment that • Critical variables for survival provides stable conditions to sustain life at the – physics of the environment cellular level (a stability or “sameness”) – limits of human physiology – internal and external environments are – length of exposure independent of each other – behavioral adaptation – physiological processes (respiration, circulation, heat balance, etc) act to maintain • Physical Diversity (& courage, fitness) a constant milieu-interieur – allows only temporary and small advantage

Walter B. Cannon, Stress-Strain 1932 •Stress • It is a failure to – a threat to homeostasis from the maintain external or internal environment homeostasis when • External: temperature, pressure, exposed to hypoxia extreme • Internal: disease, strong environments that emotions lead to death. •Strain • Stability = a – the physiological response of the dynamic balance organism • altered metabolic rate • redistribute blood flow

1 Shackelton Expedition Adaptation • Adaptation: a survival response to a change in the environment – Physiological Adaptation • a functional, structural or molecular change • slow or fast response • reversible or irreversible • Stressors •Strain – Genetic Adaptation –cold – ↑ metabolic rate • natural selection – a change to the genetic code that – malnutrition – loss of muscle and fat favors survival –fear – ↓ immune function •mutation

Mutations: good or bad? Acclimatization

• Adaptations that occur over a period of • Scurvy: deficiency of ascorbic acid (Vit C) days to months in response to a change in – humans cannot synthesize Vit C the natural environment. Usually there are – Joseph Linde, British seaman, found you can more than one stressor in a natural prevent scurvy with fresh fruits and vegees. environment. • Skin coloration: white skin – Desert: hot and dry – good in northern climate to process Vit D – Altitude: cold and hypoxia – bad in southern climate: lose protection – Spaceflight: microgravity, radiation, against UV damage psychological – Diving: cold and hyperbaria

Acclimation Accomodation

• Physiological changes to the whole body • Adaptations that occur in a single cell or with repeated exposure to an artificial tissue to an environmental change change in the environment. Usually one – increased size of sweat glands--heat specific stressor is induced. – decreased sensitivity of peripheral blood vessels –heat chamber to vasoconstrict--cold – altitude chamber – increased muscle mass--exercise –pressure chamber – decreased sensitivity of chemoreceptors— –bed rest? hypoxia – dark skin—tanning booth • Changes associated with acclimation

2 De-acclimation and de- Habituation acclimatization • A reduction in response to an environmental stimulus over time • A reversal of the adaptations with – less vasoconstriction in the hands with repeated removal of the stressor(s) cold water immersion • Variable time-courses for different – less increase in heart rate with repeated heat exposure adaptations

– less drop in arterial PO2 with repeated altitude • Different temporal relationships to their exposure rate of onset – less airways constriction to pollutants – 2 wks to heat acclimate, 4 wks to lose acclimation • Responses are often a sign of acclimation

Mediators The stress response • Biological, social or psychological factors • Hans Selye, 1937 that modifies the rate or degree of strain – all types of acclimation invoke a non-specific to a stressor stress reaction: a general adaptation syndrome –age • Stress and adaptation involve interaction –fitness between the nervous, endocrine and – fluid intake (heat acclimation) immune systems – body fat (cold adaptation) – previous experiences – personality characteristics

Key pituitary hormones for all The hypothalamus types of acclimation

•ACTH – adrenal corticosteroids (eg. Cortisol) •TSH – thyroid hormone • Regulates body temperature, sleep, appetite •AVP • Connects CSF, higher brain, spinal cord, pituitary • Secretes neuropeptides that stimulate pituitary to release hormones

3 Sympathetic/adrenal/medullary axis (SAM)

• Stress activates SNS (NE) • Activates the adrenal medulla (EPI) • Causes the flight or flight response

Neuropeptides that modulate Other hormones altered by HPA and SAM axes environmental stressors

• serotonin, alters ACTH release • Initial Stress response: Catabolic • GABA (gamma-aminobutyric acid) and – growth hormone, prolactin, thyroxine endogenous opioids, inhibit HPA axis • Post-stress response: Anabolic • acetylcholine, excites release of CRH – insulin, testosterone, estrogen (corticotropin releasing hormone) ↑HPA axis • dopamine, precursor of NE

Molecular Mediators of Stress Proteins adaptation • 1970s heat shock proteins discovered • Different stressors cause the release of over 100 neuropeptides and hormones – induced by many stressors • Heat, cold, hypoglycemia, ischemia – some influence body temperature • thyroid hormone – alter protein folding, protein synthesis, or • endogenous pyrogen (IL-1) modification – some alter immune function – Protect the cells against damage •cytokines – Mechanism for thermotolerance? • heat shock proteins (HSP) – Cross acclimation?

4 Cross Acclimation Cross acclimation: example

• When humans are exposed • What stressors? to 2 or more environmental stressors, • Major risks? – positive interactions •Interactions? • humans who adapt positively to one stressor (heat) will respond better to another (hypoxia) – negative interactions • humans who adapt positively to one stressor (cold) will respond worse to another (hypoxia)

Environmental Stressors

•Heat •Hyperbaria •Dehydration • Microgravity •Cold • Malnutrition • Altitude/hypobaria •Radiation •Hypoxia • Pollution •Noise •G forces