Download Regulating temperature

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 heat
Ways 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 heat
Type 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
Abnormal
temperature
Hypothalamus either
increases heat
production OR increases
heat loss
Temperature normal
Heat gain (or reduction of heat
loss)
Process
Description
Heat
Hypothalamus sends message to muscles to involuntarily
production by contract and relax rapidly. Cannot be sustained for too
shivering
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 source
Poikilothermic
– 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


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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, have
a 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