Lecture 15: Temperature Flashcards
Thermal conformity (poikilothermy)
allow body temperatures to fluctuate with environmental temperature (exotherm)
Thermoregulation (homeothermy)
- maintain body temperature at relatively constant levels largest independent of mean environmental temperature
- Generate most body heat physiologically
- regulate body temperature (Tb) by adjusting heat protection
Regional homeothermy: core body temperature
- temperature at the interior of the body (thoracic and abdominal cavity, brain, etc)
- maintained within narrow margins
Regional homeothermy: Peripheral body temperature
- temperature of integument, limbs etc
- tends to vary considerably
ectotherms or endotherms have broader temperature range tolerance
ectotherms
metabolism vs. ambient temperature
higher metabolic rate the lower the ambient temp.
acclimation and acclimatisation are
physiological changes in response to previous thermal history
exposure to warm temperatures increases
heat tolerance, decreases cold tolerance
thermal tolerance of many species changes with
seasonal changes in temperature.
Due to: Changes in enzyme systems & changes in membrane phospholipids
thermoregulation methods: behavioural control:
controlling body temperature by repositioning body in the environment
thermoregulation methods: physiological control
- neural responses (immediate)
- e.g. modification of blood flow to skin, sweating/panting, shivering etc.
- Acclimatisation responses (long-term)
- -changes in insulation or capacity to metabolically produce heat etc.
endotherms respond to high ambient temperatures by
1) limiting heat gain
2) increasing heat dissipation
In the thermoneutral zone body temperature remains
constant & no additional energy required
Above the Upper critical temperature (above thermoneutral zone)
- zone of active heat dissipation
- -animal increases activity to increase heat loss
- –evaporative cooling
- Hyperthermia
Hyperthermia
- evaporative cooling cannot counteract heat gain
- body temperature (As does metabolism) towards upper lethal T
problems with high temperature
- denaturisation of proteins
- -structural and enzymatic
- inadequate O2 supply to meet metabolic demands
- different temperatures effects on interdependent metabolic reactions (“reaction uncoupling”)
- membrane structure alterations
- increased evaporate water loss (terrestrial animals)
how to limit heat gain:
Increased size :
- Large animals have large heat capacities and low SA:V
- -take longer to heat up
- Large animals tend to have thicker pelage
- -insulate body from external heating
increasing heat dissipation:
Specific heat exchange surfaces
- Enable heat loss through conduction/convenction/radiation
- thin cuticle
- highly vascularised
- lightly insulated
- large surface areas
- Allens rules
whats allens rule
The warmer the climate the larger the size of appendages
sweating:
Extrusion of water through sweat glands onto the skin
- passive (little energy expenditure)
- high salt loss
- no convection
- no effect on blood pH
panting:
Evaporative cooling through the respiratory system surfaces
- active (requires muscle contraction)
- no salt loss
- convection -increases cooling
- increased ventilation leading to increased pH
panting can cool ___ during high levels of activity
brain.
- Rete mirabile
- maintain brain temperature despite abnormally high body temperature
rete mirabile
heat exchange between warm arteriole blood and cooled venous blood from nasal cavity
endotherms respond to low ambient temperatures by
- increasing heat production (thermogenesis)
- limiting heat loss
below the lower critical temperature:
- Zone of metabolic regulation
- -increase in metabolism to increase heat production to balance increased heat loss
- shivering, BAT etc.
- Hypothermia
Hypothermia:
- increased metabolic production cannot compensate for heat loss
- body temperature decreases (as does metabolism)
problems with low temperatures
- thermal inactivation of enzyme faster than rates of activation
- inadequate O2 supply to meet metabolic demands
- different temperature effects on interdependent metabolic reactions (“reaction uncoupling”)
- membrane structure alterations
- freezing
Freezing:
- drastic reduction in gas function
- -liquid water vs. solid water
- drastic reduction in enzyme function
- -reduces molecular mobility
- structural disruption of enzymes
- mechanical disruption of cell membranes
- osmotic dehydration due to freezing of extracellular water
- -most important factor
thermogenesis:
production of heat, esp in human / animal
shivering: (thermogenesis)
- rapid contractions in groups of antagonistic muscles
- no useful work generated
- heat liberated by hydrolysis of ATP
non-shivering thermogenesis:
- enzyme systems activated that oxidise fats to produce heat
- virtually no ATP production
3 forms of thermogenesis
- shivering
- non shivering thermogenesis
- heta absorbed by blood in vasculature and distributed throughout the body
forms of body heat retention:
- insulation
- aggregation
- increased body size
- circulation
insulation:
- fur/hair.feathers (pelage)
- -reduce effects of convection
- Fat/blubber
- -lower thermal conductivity of integument
- low metabolic activity (low perfusion needed)
Aggregation
-reduce convection effects (cluster together i.e.penguins)
increased body size benefit when cod:
- lower SA:V
- generally thicker coats
- Bergmanns rule
Bergmanns rule
increase body size in cold climates, smaller in warm
circulation:
- reduced asking perfusion
- -limit heat loss from blood
- countercurrent exchange
- -heat transferred from arteries to veins
- -limit heat loss from extremities
organisms which deal with subfreezing temperatures
- arctic woolly bear caterpillar
- wood frog
- snow fleas
- painted turtle
ice formation damage to organisms bodies
- cells shrink
- membrane structure degrades
- damage by ice crystals
two strategies with dealing with subfreezing temperatures
- freeze avoidance,supercoiling (freezing point depression; use of antifreeze
- freeze tolerance
freeze avoidance/supercoiling
- water usually freezes below 0 degrees celsius
- supercoiing can be enhanced by addition of solutes to an aqueous solution
- -in conc of solutes, decrease freezing point
- -e.g. insects:
1) produce high levels of glycerol
2) low freezing point
3) willow gall fly larvae can supercool to -60 degrees C
freeze tolerance
ability to tolerate freezing of extracellular fluid
- must be able to cope with…
- -potential mechanical damage
- -effects of dehydration
what do Cryoprotectants do
reduce ice crystal formation e.g. glucose, ethylene glycol.
Antifreeze proteins:
Trehalose (2 glucose molecules)
