response to heat stress. thermoregulation definition: mechanisms behind temperature regulation...
Post on 25-Dec-2015
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RESPONSE TO HEAT STRESS
Thermoregulation
Definition: Mechanisms behind temperature regulation
- Humans, like all mammals (and birds) are homeotherms, they havea thermoregulatory control system
• Normal body temperature for a human being is 37° C
• The lethal core body temperature above this is 43° C
HEAT REGULATION
• Monitoring the body’s temperature is the job of thehypothalamus
• The hypothalamus promotes activities thateffect the rate of heat loss or heat production/heat retention
• Supplemented by behavioural changes suchas:
- clothing alteration - hot/cold drinks - moving to a different area
HEAT TRANSFER
Heat is transferred (lost) from one place to another byfour mechanisms:
1. Conduction: The transfer through direct contact, from molecule to molecule
2. Convection: The loss of heat to surrounding air due to movement of molecules from warm to cool areas “Hot air Rises”
3. Radiation: Heat energy in the form of infrared radiation. This energy can be given off by warm objects, and can be absorbed by cooler ones. “Feeling the sun’s heat”
4. Evaporation: Water absorbs heat until enough is present to change its state to a gas and then it carries heat energy away with it.
Rate is proportional to surface area and the temperature gradient, but inversely to the humidity!
Methods of Heat Transfer
Homeostatic Feedback Diagram
Temperature receptors sensory nerve in skin hypothalamus
detect heat motor nerve
promote heat loss effector to or carry out action decrease heat production and heat retention
Decreasing Heat Production
Only two ways:
• lowering rates of metabolic activity in cells• decreasing level of physical activity using
muscles
Cellular respiration supporting metabolism and muscle activity generates a lot of heat!
Promoting Heat Loss
1. Sweating Sweat is produced by special glands in the dermis Nervous stimulation can increase sweat production Sweat absorbs body heat through conduction and carries
it away through evaporation
water (liquid) + heat ---------> water (vapour) from body
SWEAT GLAND
2. HAIR LOWERING
• hundreds of hairs cover each square inch of skin• when raised, air is trapped around body by preventing air
flow over the body, keeping air still, allowing it to be heated• lowering the hair allows air flow over the body helping
heat transfer away from the body
3. VASODILATION
• Increase of blood flow to the skin as smooth musclerelaxes (“red-skin”)
• Diameter of vessel lumen increases, increasing blood flow • Heat is lost from the blood through conduction,
convection, and radiation
When thermoregulatory mechanisms fail…..
Causes:• Environmental heat exposure for prolonged periods• Physical activity in intense heat• High humidity levels• Consumption of alcohol, caffeine, stimulants, and
some medications may predispose individuals, asthey cause dehydration
Result: An increase in core body temperature above 37°C:
HYPERTHERMIA (hyper – above, therm – heat)
Stages of Hyperthermia
• Heat tetany – short periods of stress in intense heat(hyperventilation, respiratory problems, numbness, muscle spasms)
• Heat rash – skin irritation from excessive sweating• Heat cramps – muscle pains or spasms due to
exercise in hot weather• Heat exhaustion - heavy sweating, rapid breathing,
a fast, weak pulse• Heat stroke – body temp > 40.6°C dry skin, dizziness, confusion, ineffective sweating
PREVENTION OF HYPERTHERMIA
• Wear light, loose-fitting clothing• Wear wide-brimmed hats with vents• Avoid strenuous exercise in hot weather• Avoid enclosed spaces such as automobiles• Wear light-coloured clothing• Drink lots of liquids to replace fluids lost from sweating• Consume salt to replace amount lost from sweating• Avoid alcohol and caffeinated drinks• Use fans/air-conditioning• Rest regularly
ADAPTATIONS TO PREVENT HYPERTHERMIA
• STRUCTURAL: how the organism is genetically designed to allow it to successfully live in a particular hot environment, or to cope with periods of heat
• PHYSIOLOGICAL: internal adjustments made which will help dissipate heat, or lower heat production
• BEHAVIORAL: what the organism does to help cool itself and prevent over-heating
Behavioral, Physiological or Structural Adaptations?
1. Panting by a dog physiological2. Plants are up off the ground preventing
heat transfer by conductionstructural
3. Vasodilationphysiological
4. Pale-coloured fur and feathers reflect sunlight
structural5. Increase in transpirational rates from leaves
physiological6. Decrease physical activity levels
behavioural7. Bats urinate on themselves to promote
evaporative coolingbehavioural
8. Jack rabbits have very long ears that are rich in blood vessels to dissipate heat
structural9. Vasodilation of blood vessels near the skin
physiological10. Animals move into cooler areas
i.e. under tree canopy or into burrowsbehavioural
Cooling off………
Jack Rabbit
11. Migration of birds to cooler climatesbehavioural
12. Small size offers ability to hide under rocks or in burrows to escape the heat
structural13. Long-legged beetles/lizards absorb less
heat from the groundstructural
14. Estivation – become inactive and lower metabolism during the dryest times of year and to avoid sweltering heat
physiological
15.Leaves face directly up or down to decrease surface area hit by the Sun
structural16.Nocturnal Activity to avoid daytime heat
“do work when it is cooler”behavioural
SO… what if you’re experiencing heat stress and water loss??
Discussion: Which is best? Pros and Cons?
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