HA - cold macroenvironments

Mild hypothermia
Shivering
Numb hands
Reduced manual dexterity

Moderate hypothermia
Intense shivering
Confused
Lack of muscle coordination

Severe hypothermia
Shivering fails and stops
Collapse and semi-conscious

Unconscious
Pulse and breathing barely detectable

28C

Enhances rate of heat loss
Blows away layer of warm air around the body

No wind chill = little danger for properly clothed person
With wind chill:
50kmph = -49C
Exposed skin freezes in 30sec

Cold, wet macroenvironments

Water has 25x the thermal conductivity of air
Thus, heat is lost 25x faster
Insulative clothing not always effective in the event of precipitation

18 male pps
5 hour simulated hike in 5C with 1 hour dry and 4 hours rain with moderate wind
11 pps did NOT finish
After 2 hours rain: shivering, loss of strength/dexterity
2 pps hypothermic

Limit heat loss
Increase heat production

Prevention (limiting heat loss > increasing heat production)

Frequency of cold
Duration of cold
Predictability of cold
Degree of exposure to wind chill
Degree of exposure to water

Clothing
Housing

Traps layer of still air close for insulation
Stops wind from disrupting insulation
Removes sweat from skin

Clo

Insulation allowing person at rest to maintain thermal equilibrium at 21C in normally ventilated room

Thick insulation minimises radiative and convective heat losses
Low SA:V (round)
Bedding has similar properties to clothes
Behaviour: sleep in family groups to share body heat

Long entrance (chambered)
Raised sleeping area reduces drafts and benefits from warmer air
Warm air and blocked wind creates a warm macroenvironment

Movement
Modifying SA:V by huddling together
Eating
Activity sheduling

Increases metabolism through activity
Stamping feet and swinging arms sends blood to extremeties

Thermic effect of food
Fat/protein more energy dense (requires more energy to digest, producing heat)
Vitamin C raises skin temp
Alcohol has short term benefits but long term problems

Avoid wind and water
Physical work during cold periods to generate heat

High protein and high fat increase metabolic heat production
Few plants except during short summer, micronutrients gathered from other sources
Marine mammals very important
Fat is prized and eaten whenever possible
Fat soluble micronutrients eg. vitamin A and D
Organ meats (especially raw) = vitamin C
Healthy and varied diet for the environment

Nonsense mutation in the TBC1D4 gene
Variation in fatty acid desaturase genes

Affects glucose metabolism of native Greenland Inuit
Nonsense mutation in TBC1D4 gene, allele frequency = 17%
Associated with reduced glucose uptake in muscles, thus increasing risk of type 2 diabetes
BUT adaptation to high lipid diet, sparing glucoes availability for the brain

Variants of fatty acids desaturase (FADS) genes involved in fatty acid metabolism
Likely an adaptation to high levels of omega-3 polyunsaturated fatty acids (PUFAs) from a high fat, marine diet
Results in lower body mass and reduced stature

DNA sequence change gives rise to a stop codon rather than a codon specifying an aa
Presence of new stop codon results in shortened protein, likely non-functional.

Reduce heat loss
Metabolic adaptation to preserve and generate heat

Subcutaneous fat
Body size/shape: Bergmann and Allen's Rules
Vasoconstriction
Horripilation

Increased basal metabolism
Voluntary and involuntary metabolism
Brown fat activation

Subcutaneous fat acts as an inuslator - BUT muscle mass is better

Human populations in cold regions, Korean free divers and Polar Bears do not have very elevated subcutaneous fat
So little/no evidence for body fat adaptations in cold macroenvironments

Larger, more globular cranial vault
Flatter / broader faces
Taller, narrower noses

Minimises SA:V

Width of the nares correlated with temp and absolute humidity (but not relative humidity)
Some nose shape aspects potentially driven by local climate adaptation
Has complex evolutionary history, possibly involved other non-neutral evolutionary processes (sexual selection)

Diverting blood from shell to core

Blood redirected to visceral organs
Extremeties have high SA:V causing high heat loss through surface

Too much/prolonged vasoconstriction can lead to frostbite

Cold induced vasodilation (CIVD)
Occurs 5-10mins after cold exposure
Increased with frequent cold exposure
Skin temp < 10C
Waves of vasodilation/vasoconstriction to the extremeties
Helps maintain normal function and prevent frostbite/tissue death
Humans have limited CIVD compared to other species

Contraction of arrector pili muscles at base of hair follicles
Traps insulative air next to skin
Not very effective in humans

When insulative heat mechanisms are insufficient

Non-shivering thermogenesis = increase in metabolic heat production (above the basal metabolism) that is not associated with muscle activity
Plasticity in basal metabolic rate
Involuntary muscle contractions (shivering)

Amount of energy expended at rest
Increased by:
- Cold exposure and acclimatisation
- Populations indigenous to cold environments relative to predictions from body surface area, mass and fat-free mass

Number of calories your body needs to accomplish its most basic (basal) life-sustaining functions

Thyroxine

Induced by cutaneous cold receptors
Starts in trunk/proximal, moves to extremeties
Can double/triple basal metabolic rate
May generate up to 1,200kJ/hr
Regulated by negative feedback loop

White
Beige/Brite
Brown

Low mitochrondial density
One large lipid droplet
Main functions = energy storage, endocrine

Medium mitchodrial density
Few to many lipid droplets
Main functions = thermogenesis? endocrine?

High mitochodrial density
Numerous lipid droplets
Main functions = thermogenesis, endocrine

Important role in infants but also found in adults
Primary function = thermoregulation

Expressed uncoupling protein 1 (UCP1)

Releases heat instead of producing ATP

BAT mass increased in animals fed high fat diets (high fat in Arctic diets)
Evidence of long-term adaptation affecting brown fat cells (same thing as BAT) in indigenous populations from cold climates (signs of selection near TBX15, involved in development and differentiation of brown fat cells)

TRPM8 (depends on the allele of this gene)

Senses moderate cold
Several signs of positive selection in Eurasian populations in last 25,000 years
Rare in Africa, more common outside
Frequencies strongly correlate with latitude
Associated with migraines - potential costs of cold adaptation?

0C air and 10C water in winter
30% increase in basal metabolic rate in winter
Non-shivering thermogenesis
Blunted/delayed shivering response
Can torelate core temp of 35C
Insulative cold acclimatisation involves peripheral blood flow

More cold tolerant
Time to shivering delayed
Increased BAT activation - evidence of plasticity in response to cold
Beter vasoconstrictive response and heat conservation at body shell
Maintenance of optimal blood perfusion to the skin

Macroenvironment: arctic (seasonal intense cold, predictable), high altitude (diurnal cold, predictable), arid habitats (diurnal cool, predictable)
Leads to behavioural/cultural buffer: clothing, housing, bedding, activity scheduling, alcohol/drug use, fire/cooking
Essential resources: clothing, bedding, housing
Potentially leads to biological buffer: body form (SA:V), subcutaneous fat, vasoconstriction, CIVD (cold induced vasodilation), shivering
Demographic effects: infants, some occupational groups

Process of oxygenated blood being delivered to the body's tissues