Transcript Bio6AslidesEnergyandThermore

Energy and
Thermoregulation
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Maintaining internal environments:
Challenge for all living environments
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Regulators: use internal
control mechanisms to
regulate internal change
in the face of fluctuations
in the external
environments.
Conformers: allows
internal environment to
conform to external
changes (for a particular
environmental variable)
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Regulating and conforming are extremes
of a continuum: Organisms may conform to
some environmental factors and regulate
others. e.g. fish – thermoconformers,
osmoregulators.
Homeostasis (steady state): Maintaining
relatively steady internal environment even
when external environment changes
significantly.
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Dynamic equilibrium: external factors try to
change internal environment, internal control
mechanisms oppose such changes.
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Body temperature: 37oC
pH: 7.4
blood glucose: 90mg/100mL of blood
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Mechanisms of
homeostasis:
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Set point: the desired
temperature (variable)
Stimulus: fluctuations in
the variable
Sensor: detect stimulus
and triggers an
appropriate change
Response: activity that
helps return the variable
to the set point
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Home heating
system as an
example of
homeostasis
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Do you see the
machanism of
homeostasis
here ?
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Negative feedback loop: response that
reduces the stimulus. (exercise and sweting)
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Positive feedback loop: responses amplify
the stimulus (labor)
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Regulated changes of setpoint: e.g. temperatures
change when asleep and awake, hormone levels in
women’s menstrual cycle
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Acclimatization: change in normal range of
homeostasis in response to internal environment.
e.g. increased blood flow and red blood cell
production
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Acclimatization is not adaptation – acclimatization
is temporary; adaptation is natural selection working
on a population over several generations.
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Homeostatic process for thermoregulation:
Essential to maintain internal temperatures
within “tolerable” range.
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Enzymes have narrow optimal temperature range.
10oC change in temperature reduces enzyme
activity 2 to 3 fold
Proteins start to denature and loose activity
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Endothermy: warm
themselves by heat generated
by metabolism (birds and
mammals). Have ways of
warming and cooling their
bodies. Consume more food
than ectotherms
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Ectothermy: gain their heat
from external sources
(amphibians, lizards, snakes,
turtles, fishes). Mostly change
body temperature by behavior.
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Endotherms may have some
ectothermic behavior. Two
strategies are not mutually
exclusive.
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Poikilotherm: Animal whose temperature
varies with environment
Homeotherm: Has a relatively constant
body temperature
Common misconception: poikilotherms are
coldblooded; homeotherms are
warmblooded.
Balancing heat loss and
gain:
 Heat exchange is
regulated by four
physical processes:
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Conduction
Convection
Radiation
Evaporation
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Thermoregulatory organ: major role played by
the integumentary system (skin, hair, nails, fur,
scales, claws)
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Theromregulatory adaptations:
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Insulation
Circulatory adaptations
Evaporative loss of heat
Behavioral adaptations
Adjusting thermogenesis
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Theromregulatory adaptations:
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Insulation
Circulatory adaptations
Evaporative loss of heat
Behavioral adaptations
Adjusting thermogenesis
Insulation:
 Prevent flow of heat
between animal and
environment
 Hair, feather: traps air
and insulates, raising
hair traps more air
 Goose bumps
 Some animals ooze oil
into their hair to prevent
them from getting wet
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Theromregulatory adaptations:
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Insulation
Circulatory adaptations
Evaporative loss of heat
Behavioral adaptations
Adjusting thermogenesis
Circulatory adaptations:
 Regulate blood flow near body
surface and maintain core
body temperature
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Vasodialation: nerve signals
relax muscles of the superficial
blood vessel walls, increased
blood flow to the surface, heat
directed to the skin, increase in
surface temperature, heat
dissipated by radiation,
example: jack rabbits ears
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Vasoconstriction: Diameter of
superficial blood vessels
decrease, reduces blood flow
to the surface and prevents
heat loss.
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Circulatory
adaptations contd….
Countercurrent
exchange:
arrangement of tissues
and blood vessels in a
particular way that
maximizes heat
exchange.
Example: goose and
dolphin;
Skin
Artery
Vein
Blood
vessels
in gills
Capillary
network within
muscle
Heart
Artery and
vein under
the skin Dorsal aorta
Great white shark
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…..also helps maintain
core body temperature
in essential tissues, like
flight muscles
21°
25° 23°
27°
29°
31°
Body cavity
Bluefin tuna
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Theromregulatory adaptations:
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Insulation
Circulatory adaptations
Evaporative loss of heat
Behavioral adaptations
Adjusting thermogenesis
Evaporative heat loss:
 Water evaporates
considerable heat
during evaporation
 Panting in dogs
 Sweating
 Fluttering of pouch at
the base of the mouth
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Theromregulatory adaptations:
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Insulation
Circulatory adaptations
Evaporative loss of heat
Behavioral adaptations
Adjusting thermogenesis
Behavioral responses:
 Migration
 Body orientation
 Hibernation
 Bathing
 Huddling
 Storing high calorie
food (honey)
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Theromregulatory adaptations:
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Insulation
Circulatory adaptations
Evaporative loss of heat
Behavioral adaptations
Adjusting thermogenesis
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Adjusting thermogenesis:
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Shivering thermogenesis: heat production as a
result of increased muscle activity
Nonshivering thermogenesis: some specialized
chemical reactions results in heat production
instead of ATP in mitochondria
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Adjusting thermogenesis contd…
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Some ecothermic animals can do some endothermic
regulation (egg incubation by Burmese python, resulting
from spasmodic muscle contraction)
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Adjusting thermogenesis contd…
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Some insects perform “warm-up” preflight shivering to get
critical muscles warmed up
Acclimatization in Thermoregulation:
 Thicker coat during winter
 Enzymes with different optimal temperatures but same
function
 Cells with antifreeze compounds
Physiological thermostats – temperature regulation
in humans:
Fever: increase in set point of body
temperature in the hypothalamus, for
instance – response to infections
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Fever has some defensive functions
Fever is observed in endotherms
Ectotherms have behavioral adaptations that
function like development of fever, during an
infection
Bioenergetics:
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Related to animal’s size, activity, environment
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Determines food need
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Overall flow and transformation of energy in an
animal
Energy allocation and use:
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Animals obtain energy for
various activities from food
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Food is digested in the body
by enzymatic hydrolysis
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Digested food generates
ATP as a result of cellular
respiration
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ATP is used for
biosynthesis, growth, repair,
reproduction etc. and for
generating heat
Quantifying energy use:
 Metabolic rate: sum of all energy requiring
biochemical reactions over a given time interval.
 Can be measured by heat production, carbon dioxide
production, food consumption etc.
Basal Metabolic Rate (BMR): Minimal
metabolic rate of a nongrowing endotherm at
rest, in an empty stomach, at comfortable
temperature with no generation or shedding
of heat.
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Human males – 1,600 to 1,800 kcal (C) per day
Human females – 1,300 to 1,500 kcal per day
Standard metabolic rate (SMR): metabolic
rate of a fasting nonstressed ectotherm at a
particular temperature.
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Alligator – 60 kcal per day
Maximum metabolic rate (MMR): Highest
rate of ATP use; is inversely related to the
duration of the activity.
Size and metabolic rate:
 Relationship between metabolic rate and
body mass is constant across a wide range of
sizes and forms
 Metabolic rate is roughly proportional to the
body mass, to the ¾ power (m ¾)
 The reason for this is not yet known
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Energy budgets:
Torpor, Hibernation, Energy conservation:
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Physiological state of low activity, low
metabolism, body temperature drops,
allowing the animal to save energy and avoid
situations where it is more vulnerable
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Hibernation is long term torpor.
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Small animals with higher metabolism go into
torpor;
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bats torpor during the day,
hummingbirds at night.
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Certain squirrels show prolonged torpor with brief
arousals in winter.