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Regulating temperature
External temperature change
Detected by heat and cool receptors on skin
External temperature may fluctuate without damage to humans
Internal temperature change
Detection by receptors within body Receptors in hypothalamus of brain
are most important Some also near spinal column, around
veins, in digestive system All send messages to hypothalamus
Hypothalamus
Detects and receives messages about temperature change
Temperature control centre
Maintaining core temperature
Mammals = 37 degrees Celsius At any time mammals both lose and
produce heatWays of gaining heat Ways of losing heat
Basic metabolic processes Evaporation of sweat
Shivering Panting
Exercise/ vigorous activity Convection
Radiation and conduction to body
Radiation and conduction from body
Loss of heatType of heat loss What is it? How much heat
is lost?
Radiation - Heat radiates from body in all directions.- Can also be absorbed by body from hotter objects
~60% of heat loss
Conduction and convection
-Transfer of heat from body to objects or substances that are touched. -Touched objects must be cooler than body temperature- If air surrounding body is moving (wind), convection currents take heat away from body-Convection occurs much faster in water than air
~ 15% of heat loss
Evaporation -Occurs even when person is not “sweating”- Requires heat provided by body
~22% of heat loss
Temperature regulation by hypothalamus
Normal temperature
Check temperature
Temperature normalAbnormal temperature
Hypothalamus either increases heat production OR increases heat loss
Heat gain (or reduction of heat loss)
Process Description
Heat production by shivering
Hypothalamus sends message to muscles to involuntarily contract and relax rapidly. Cannot be sustained for too long due to energy requirements.
Heat produced by metabolism
Hypothalamus stimulates the pituatary gland, which then stimulates the thyroid, which increases its output of hormone thyroxine, which increases the metabolic rate in every cell in the body, releasing heat energy.Adrenaline can also be stimulated, which also increases metabolic rate
Constriction of blood flow in skin
When cold, blood vessels shrink, which decreases the surface area of the blood vessels, from which heat can escape. Blood vessels are also removed from the skin surface, keeping heat within the body
Piloerection “Hair standing on end”. Not important for heat conservation in humans, but in other mammals, erect hairs trap air close to the body, which acts like a doona.It is caused by the contraction of muscles at the base of the hair.
Cooling down behaviour
Animals that don’t sweat will lick their paws
Seeking out a cool position to sleep (conserve energy and therefore heat)
Increase surface area, which increases the area by which heat can leave the body
Drinking water doesn’t cool us down, but reduces the danger of dehydration/ dessication
Size matters
A small animal will lose heat more quickly than a larger animal because of an increase in SA:V ratio
Therefore, the metabolism of an animal with a large surface area is much quicker, as it must produce more heat energy to maintain its temperature
Heat sourcePoikilothermic – Have a fluctuating (changing) body temperature
Homeothermic – have a constant body temperature
Endothermic – heat source is built into body
Camels Humans
Ectothermic – temperature is reliant on external environment
Reptiles None – too fragile
Ectotherms need significantly less food than endotherms. Why do you think this is?
Activities
Glossary: ectothermic, endothermic, poikilothermic, homeothermic, hypothalamus, pituatary, adrenalin
Quick Check questions pg 317
Land animals: adaptations to heat Spinifex mouse
Lives in well insulated burrow to keep temp. fairly constant
Endothermic
Land animals: adaptations to heat Snakes
Bask in sun to heat up (ectothermic) Cold at night More active during day than night Cannot engage in prolonged strenuous
activity, as lactic acid builds up in ectotherms’ muscles
Some snakes may flatten themselves while basking (why?)
Blood flow near skin is high while basking to heat blood as much as possible
Land animals: survival in cold
Ice can be deadly Enzymes do not function quickly Chemical reactions often happen in
water. They cannot happen in ice. If a cell freezes, the ice crystals will
expand and rupture the cell membrane.
How to prevent freezing
Increased dissolved salts in antifreeze substances that can be released into body fluids Glycerol, amino acids, sugars, salts Decreases freezing point of water (to
about -18 degrees C)eg. Insects, fish, turtles, frogs
How to prevent freezing
Increased body fat (insulation)
Conversion of food to heat energy (eg. birds and mammals)
Lower surface area to reduce area of heat loss
Behavioural prevention of freezing Burrowing underground (insulation)
Migration
A long sleep
Some animals hibernate or go into a torpor
Metabolism is drastically reduced (can be as low as 0.6% of normal rate) so animal only barely lives
Body temp drops to environmental temperature
Mountain Pygmy Possum lives in alpine areas of Victoria and NSW
Animals surviving in water Aquatic environments have less temperature
variation than terrestrial environments Maintenance of body temperature may be by
counter-current systems to warm the blood Outgoing artery paired with incoming vein. Therefore,
blood cooled by being close to the skin is warmed by artery blood before reaching the inner core of the body
Otherwise, aquatic mammals,like dolphins/whales/seals, havea thick layer of fat (blubber) to insulate against the cold water
Lack of oxygen in aquatic mammals Aquatic mammals live largely under
water but must breathe gaseous oxygen Higher oxygen carrying capabilities in
blood Large lungs and other respiratory
structures Storage of oxygen in other body tissues
Activities
Glossary: counter-current, hibernation, torpor, antifreeze
Quick Check questions pg 322