Climate Flashcards
What is human variation the result of?
Genetic drift, gene flow, genetic adaptation (through natural selection) to environmental conditions both past and present, physiological and cultural responses
Human plasticity
Includes physiological/cultural responses to environmental changes
Environmental Stress
Environmental Stress is any condition that disturbs the normal functioning of an organism, this eventually disturbs the organism’s homeostasis
Homeostasis
Homeostasis is when the body of an organism has a consistent and relatively stable internal environment and is maintained by feedback loops
Common forms of environmental stress
Ultra violet radiation Heat stress Humidity Stress Cold Stress Altitude Nutritional Stress Disease Stress Population Pressures
Hot and cold stress
- Both ancient stresses on humans
- Cause less loss of life than malnutrition and disease
- Because humans are better adapted to hot and cold stress
Ideal Internal Core Temperature
37-37.6: ,more than a few degrees either direction from this range is fatal
Ways of adapting to hot and cold stress
Adaptation: Evolutionary change
Accommodation: responses that ensure survival but many have a long term cost
Developmental adjustment: Adjustments to physiology in response to the environment during developmental stages
Acclimatisation (acclimation): gradual, reversible adjustments in response to changes in environments
Behavioural/Cultural responses: responses that are learnt and culturally and environmentally specific e.g wearing warm clothing or sun cream
How can the body heat up when cold?
- Increased metabolism
- exercise or shivering
- hormone-induces increase in metabolism
- infection (i.e. fever) - Non-shivering thermogenesis (induced by hormones)
- Conduction (touching hot things)
- Convection (contact with hot air)
- Radiation (receiving infrared waves)
What increases your risk of freezing to death
-Highest mortality rate in infants, the elderly, the poor, alcoholics and those who are in water
What else can help warm you up?
- Subcutaneous fat (developmental adjustment?)
- Muscle (developmental adjustment?)
- Avoiding cold (behavioural/cultural response)
- Wearing protective clothes (behavioural/cultural response)
- Favourable body proportions (developmental adjustment)
- Higher resting metabolic rate (adaptation, behavioural response)
- Lower core temp, delayed shivering, increased non-shiveering thermogenesis (acclimatisation-within 5-10 days)
- Hunters waves (adaptation, accommodation?)
- Protruding, narrow nose (adaptation)
Body Proportions
Bergmann’s Rule (1847)
-People closer to the equator are less bulky than people who live in cold areas
Allen’s rule (1877)
-People closer to the equator have longer limbs than people who live in cold areas
What increases your risk of heating to death
Infants, elderly, the poor, elite athletes, workers
Heat and metabolism
Humans produce a lot of heat constantly through metabolism, whether exercising or not
This means when core body temperature is high, physical activity adds stress (the opposite of what happens with cold exposure)
Responses to heat
Involves vasodilation, conduction, radiation, evaporation and behaviour/culture
- Internal heat moves by conductance and vasdilation to the body surface where it can radiate away
- Sweat glands produce sweat which evaporates to cool the skin (more difficult in humid climates)
- Ventilation
- Early/Late working and siestas
- Clothing styles
Heat Acclimatisation (7 days-8 weeks)
- Increased plasma and blood volume
- Low sodium sweat
- Lower threshold for sweating and vasodilation
- Reduced heart rate (with more efficient beating)
- Reduced metabolic rate
- Re-absorption of sweat
- Lower core temperature
- Recognising when to stop
High Altitude
- Considered 2500 meters and higher above sea level
- At these altitudes there is lower barometric pressure, leading to fewer oxygen molecules per breath
- Hence, hypobaric hypoxia
- Reduced oxygen in air and reduced ability to get oxygen from the air
- 33% of the oxygen at sea level is at the top of mount Everest
- Highest point of human habitation has 55% of the oxygen that there is at sea level
Illness related to altitude
Acute mountain sickness:
-usually visitors
-headache, nausea, vomiting, anorexia, fatigue, breathlessness
-sometimes pulmonary edema and cerebral edema
Chronic mountain sickness
-can happen to people who are well-adapted and long-staying at high altitudes
-headache, dizziness, tinnitus, breathlessness, palpitations, sleep disturbance, fatigue, anorexia, mental confusion, cyanosis, and dilation of veins
-bone marrow produces too many red blood cells, level of oxygen in blood low
Altitude Acclimatisation
-Hypoxic ventilatory response - breathing becomes deeper and faster (temporary)
Increased concentration of haemoglobin in the blood
-higher heart rate (temporary)
-Inactive capillaries open
-Tissues in lungs more full of blood
Athletes are more negatively affected and cannot resume physical work capacities as quickly as others
Altitude Adaptation
- Higher resting ventilation rates
- Larger lung volumes
- elevated haemoglobin levels
- Fetal oxygen transport improvements in the placenta
- Greater uterine artery blood flow
- Shorter stature?
- Larger chest dimensions?
High altitude Tibetans
Ethnic Tibetans possess heritable adaptations to low oxygen availability
- high oxygen saturation of blood (associated with red blood cell production) but no IUGR or foetal mortality (due to blood viscosity)
- One single-nucleotide polymorphism associated with red blood cell production
- Shows a 78% frequency difference between Tibetan and Han Chinese samples, who only diverged c3000 years ago
- Faster rate than the spread of lactose tolerance in northern Europe, which took 7500 years
