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LU5: THERMOREGULATION (by 51494 & 54020) (How animals keep body warm…
LU5: THERMOREGULATION (by 51494 & 54020)
Thermoregulation
:
regulation of body temperature to
maintain homeostasis
i)
Thermoregulator
-
regulates own body temperature
(
e.g.: birds & mammals
)
ii)
Thermoconformer
-
UNABLE
to control own body temperature
(
It fluctuates with
external temp.
)
1)
Ecto
therm
Maintains body temp by
gaining heat from external sources
Produce
low
metabolic heat
Food requirement -
Lesser
Enzyme activities
- NOT at optimal
Small difference
between body temp. & external temp.
e.g.: fish, invertebrates, amphibians
2)
Endo
therm
Maintains body temp via
metabolic heat production
Food and energy requirement -
High
Enzyme activities
at optimal
-
Large differences
between body temp. & external temp.
e.g.: birds, mammals
Poikilo
therm:
-Internal temp.
varies considerably
e.g.: Reptiles
Homeo
therm:
-
Stable temp.
(maintains thermal homeostasis)
e.g.: Human
Temperature Coefficient (Q10)
The
rates of biochemical reaction
&
physiological processes
due to body temp. changes
Q10 = (R2/R1)*[10/(t2-t1)]
Crucial for
poikilotherm
Body temp. depends on:
External environment fluctuation &
Biological mechanism
Thermoneutral range
Temp. range when the:
Animal feels
comfortable
Metabolic heat production
remains constant
Acclimatization
Changes in temp.
in response to climatic change
Adaptation of a
gradual change
in
external environment
High temperature causes...
Protein denaturation
Inactivation of enzyme reaction
Increase of metabolisms (higher demand of oxygen)
Over-accumulation of metabolites & wastes
Destruction of membrane structure
Death (combination of all factors)
Fall off of Q10
Animals that can survive OUT of the LIMITED temp.
of
-2 to 50 degree celsius
A)
Eggs
of
freshwater crustacean
Survive in dry mud (summer):
80oC
In lab:
99oC
B)
Cyprinodon diabolis
Warm water :
34oC
(lack of oxygen)
Upper lethal temp.:
45oC
C)
Artic fish
Upper lethal temp.:
6oC
Has been observed to survive at
-2oC
How animals survive at extreme low temperature?
A)
Freeze tolerance
Survive
even
ice formation occurs in bodies
Low tide,
Freezing
(extracellular fluids) &
remains unfrozen
(intracellular fluids)
e.g.: aquatic invertebrates
High tide,
body temp. same as water temp
; Not frozen
B)
Supercooling & anti-freeze compounds
Supercooling
:
-
Pure water can readily be cooled down to
* -20oC before freezing
Anti-freeze compunds
which:
-
Lower freezing points
-
Prevent formation of ice crystal
e.g.: Arctic / Antarctic fish
Glycerol
Lowers
both
freezing & supercooling point
Minimum freezing point:
-37.8oC
e.g.:
Gallfly
in Alaska can survive at
-60oC
with
50% glycerol
How body temperature heat is transferred?
A)
Conduction
:
-
Physical contact between
2 surfaces with differing temps.
B)
Convection
:
-
Flow of air / liquid
over a body surface
C)
Radiation
:
-
Transfer of heat between objects that are
NOT
in direct contact
D)
Evaporation
:
-
Liquid to vapour
-
Heat releases from surfaces
How animals keep body warm in the cold?
-
via voluntary muscular activity
A)
Shivering
:
-
Involuntary
muscle contraction & relaxation
-
Increases body heat
production
B)
Vasoconstriction
:
-
Constriction of blood vessels
-
Decreases blood flow
-
Reduces heat loss
C)
Piloerection
:
-
Skin hairs standing
-
Traps the surrounding warm air
D)
Non-shivering thermogenesis
:
-
Increases metabolic heat production
e.g.
hibernating mammals
& human babies
E)
Become fats and hide in burrows (hibernate)
-
Smaller mammals
cannot have too thick fur - impedes movement
e.g: squirrels, penguin & honeybees
G)
Thick fur & subcutaneous fat
:
-
Larger mammals
e.g.:Polar bear
H)
Bask in sun
:
-
Warm their body
-
Develops dark pigment
-
increase net environmental heat gain
e.g.:Grasshoppers
I)
Cover feet with feathers
:
-
External
insulation
J)
Thick layer of fat
-
Internal
insulation
-
Increases metabolic rates
-
Aquatic animals
(e.g.: Whales & seals)*
F)
Superficial hairs (insulator)
:
-
keeps body warm
e.g: Bumblebee
K)
Counter-current heat exchange Mechanism
:
-
Allows flowing of
2 fluid with differing temp. in opposite directions
-
Minimizes heat loss
-Blood vessels special arrangement:
(
Thick
walled
central artery
surrounded by
Thin
walled
peripheral vein
)
Torpor
Natural hypothermia
Depression
in metabolism, respiratory rate & heart rate
Lack of response
to
external stimulation
Temporary
hibernation
(short-term)
Hibernation
Voluntary state
of sleep
(extended form of torpor)
Breathing
slows down
Body temp.
lowers
Before hibernating, animals
becomes fat
Lower
metabolic rate
Hormonal thermoregulation in terrestial mammals
Sensory neurons
-
temperature-sensitive
Temperature receptors
:
i) Ruffin Organ (
warm
)
ii) Bulbs of Krause (
Cold
)
Epinephrine
Immediate
response
Increases metabolic rates (ATP usage)
Increases heat
Thyroxine
Takes
days to weeks
to occur
Increases catabolism (nutrients)
Increases metabolism & ATP production
Increases heat
Brain temp. monitoring - by
Hypothalamus
How animals keep their body cold under hot sun
A) Physiological adjustments
:
-
Increase blood flow
-
Increase heat loss (evaporation)
B) Vasodilation
:
-
Dilation of blood vessels
-
Increases blood flow
-
Increases heat loss
C) Sweating
:
-
Sweat evaporates
-
Cooling body
D) Panting
:
-
Cooling of blood to the brain
e.g.: Dogs, birds
E) Smaller animal with larger body surface area:
-
Losses heat faster
G) Flat ears / spray body wih water
:
-
Removes heat via
convection
/ evaporative cooling
e.g.: Elephants
I) Estivation
:
-
Sleeps away during summer
-
Reduced metabolism until stress is over
e.g: Squirrels,mammals & desert animals
H) Lick body with saliva
:
-
Cooling
e.g.: Marsupials
F) Hide in burrows
(during day):
-
Conserve water (avoid over-heating)