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Year Two - ENI - SDL - Thermoregulation in Exotics
Terms in this set (41)
What are 5 differences between homeotherms and poikilotherms?
1. Homeotherms have a constant body temperature, whereas Poikilotherms' body temperature adjust depending on the environment
2. Mammals and birds are homeotherms, whereas reptiles and fish are poikilotherms
3. Homeotherms can only survive if their body temperature is within a narrow range, whereas poikilotherms can survive with their internal body temperature varying over a wide range
4. Homeotherms use less resources as their enzymes are highly efficient due to operating within a narrow temperature range - grow larger and develop faster, whereas poikilotherms use up a lot of resources producing inefficient enzymes which can operate over a wide range of temperatures
5. Homeotherms' internal metabolism maintains heat, whereas in poikilotherms outside temperature maintains heat
What is the habitat range of homeotherms?
More able to adjust to different environments due to internal temperature regulation
What is the habitat range of poikilotherms?
Reliant on environmental temperature so less able to live in a variety of environments
What are the activity levels of homeotherms?
High activity levels due to efficient enzymes
Grow larger and develop faster
What are the activity levels of poikilotherms?
Reduced activity levels as the focus of their enzymes are more inefficient due to them needing to be able to work over a wider range of temperatures
Limited over a range of temperatures
What are the food/ energy requirements of homeotherms (3 points)?
A large proportion of their energy intake is used for thermoregulation
Constrains where they can live based on securing/ storage of energy sources
Higher food requirements
What are the food/ energy requirements of poikilotherms?
Reduced food/ energy requirements due to no internal regulation of body temperature
What are melanophores?
Melanophores = specialised cells derived from the neural crest that contain membrane-bound vesicles (melanosomes)
Melanosomes = filled with melanin, a dark, non-fluorescent pigment that plays a role in physiological colour adaptations of animals
What is the role of melanophores in thermoregulation?
Melanophores contract (when hot) or expand (when cold) as a reaction to temperature changes
Can concentrate or spread out the amount of melanin by absorbing skin - darker = absorbing light/ heat, light = reflecting light/ heat
What are 5 specific physiological adaptations of amphibians to lower the freezing point of their tissues to aid survival in winter temperatures?
Push up to 65% of their water outside of cells - this means the water freezes in pockets below the skin around the skeletal muscles
Make molecules in their tissues (e.g. glucose) to protect their cell volume = cryoprotectants - work by changing the properties of fluids inside the cells, protecting against the cold
Slow metabolism whilst frozen - become somewhat dormant and use less energy = hibernation state
Increase plasma osmolarity via dehydration
Ice nucleating proteins guide ice formation so it doesn't damage cells when ice forms
What is POTZ?
Preferred optimum temperature zone
What is the importance of the POTZ?
It is the optimum temperature for the functioning of reptiles' systems, e.g. movement, feeding, digestion, reproduction and immunocompetence - due to the environment regulating their temperature, which means they have a specific environment/ temperature they need to be in
What processes may cause the POTZ to vary for an individual animal?
Can be due to the different levels of activity, how often they feed, how long the animal takes to digest food, how often they reproduce etc...
What is the clinical significance of providing the appropriate environmental temperature for your poikilotherm patients?
Sick reptiles tend to seek out the high end of their POTZ, which is known as 'behavioural fever' - have the best chance of resisting disease, needs to be at the right temperature for bodily processes
In reptiles, what area of the brain is involved in controlling thermoregulation and how does this area receive its input?
Pre-optic nucleus in the hypothalamus
Input from blood in the carotid artery have sensors that allow for changes
What is behavioural fever?
When sick reptiles seek out the higher end of their POTZ - can't have a fever themselves so seek higher heat to 'make' one
For what 2 reason is behavioural fever significant clinically for poikilotherm patients?
Helps you to identify illness by temperature as signs aren't always obvious until late on in the disease process in reptiles (may be difficult to tell)
Need to provide a range of temperatures so they can choose where to be
How does behavioural fever in poikilotherms differ from a homeotherm's response to infection?
Homeotherms - internal temperature increases (increase their set point) outside the narrow temperature range, indicating illness in the form of a fever
In what 2 ways do snakes and lizards change their body shapes for thermoregulatory purposes?
Coil up to help protect from the heat - face the sun when hot as less of the body is in contact with the sun, stand on tip-toes to elevate body so its not pressed against the floor etc...
Bask in the sun (stretched-out posture, lie flat) to maintain body temperature - perpendicular to the sun = more of the body warms up
What is gular fluttering?
When a bird open its mouth and flutters its upper throat muscles (seen in some species more than others but all birds do it to some extent)
How does gular flutter help some animals with thermoregulation?
Promotes heat loss - similar to dogs panting and humans sweating
Increases blood flow to the buccal area, allowing for heat to be lost by driving air across the moist areas
What are 2 cardiovascular adaptations that exist in reptiles to aid with thermoregulation?
Core is warmer than the periphery - want to shift blood out to the periphery, so by increasing the heart rate there's an increase in movement of blood from the warmer core to the cooler periphery - daytime when warm = more vasodilation - increases blood flow to periphery, night when colder = more vasoconstriction, decreased heart rate - sends blood back towards the core to prevent heat loss
3 heart chambers - right to left cardiac shunt, avoids the lungs and therefore avoids evaporative cooling
Why do many reptiles lose and absorb heat rapidly?
High SA: body mass ratio = can lose or gain heat rapidly - can be a problem if trying to prevent heat loss
What is the trigger for hibernation in reptiles?
Adverse weather conditions - e.g. reduction in temperature or light intensity, decrease in day length = temperature drop (owner can decrease temperature to trigger hibernation)
How does the trigger for mammal hibernation differ from that of reptiles?
Mammals - triggered by a change in the animal's habitat, recognise shortening days and falling temperatures = detect the onset of winter - the scarcity of food = main trigger)
Why might a captive snake not hibernate?
No hibernation - if the owner doesn't artificially manipulate the temperature to cool the environment and photoperiod to mimic that of where they animal would live in the wild - constant source of heat and light all year round in captivity
Why might a snake not hibernating be a problem if an owner wants to breed it?
Hibernation allows for the increased production of sperm in males and helps females prepare for ovulation in the spring
What are digestive processes in reptiles dependent on?
Temperature - won't digest if too cold
Why do you think it's important for a reptile to be fasted a week or two before entering hibernation?
If the animal goes into hibernation and they haven't digested food, it could lead to intestinal blockages and/ or gut stasis that could kill the animal as they can't digest in the cold
Food could also rot, causing infection
What 3 cardiovascular adaptations do birds have for shedding or conserving heat?
Counter-current exchange system - the 2 streams often have different temperatures, helps to reduce heat loss from naked extremities (e.g. feet)
Tibio-tarsal retes (particularly in aquatic/ wading birds) - returns body to core to save heat
During heat stress in order to shed heat birds shunt blood from the left ventricle to the legs (no feathers)
Why are small birds particularly sensitive to draughts?
Heat loss occurs due to convection when there is a draught, meaning birds must increase their metabolic rate to say worm
Smaller birds have a higher surface area: body mass ratio, which means body cooling is more rapid
What nutritional implications does this have for smaller birds subject to chilly conditions?
Would require a higher food intake in order to meet the increased metabolic and energy demands of a cold environment
In what 5 ways do birds use their plumage/body position to shed or retain heat?
Body heat warms the air in between birds' feathers
Birds fluff-up their plumage in the cold to trap as much air in their feathers as possible - the more air = the warmer the bird, vice versa to reduce heat retention
Tuck their heads in when cold as they're sources of heat loss - keeps them warm in the cold
Shiver pectoral muscles to make heat
Spread wings and elevate scapular feathers to lose heat
How does the respiratory system aid in thermoregulation in birds (2 ways)?
Gular flutter to increase evaporation
Evaporative loss across air sacs
Why can shivering be sustained for longer at temperatures between 20-32 °C, but not at temperatures below 20 °C?
Aerobic muscle fibres can be used for longer and these would be used in warmer temperatures
Recruit anaerobic fibres below 20 degrees which can't be sustained for as long
What is non-shivering thermogenesis (NST)?
An increase in metabolic heat production above basal metabolism that isn't associated with muscle activity
Why can't reptiles use this mechanism of thermoregulation and why was it believed that birds didn't use NST either?
They don't have brown adipose tissue which is responsible for non-shivering thermogenesis
What is the evidence that the birds do use NST (2 pieces)?
They have avian UCP which is involved in NST
Birds can show impressive responses to cold stress by increasing their metabolic rate, which implies use of NST despite the lack of BAT
In which tissue does NST primarily take place in birds?
Skeletal muscle (approx. 70%)
Rest is in the heart, liver and other tissues
How is the pineal gland involved in thermoregulation in birds (2 ways)?
It prevents rise in body temperature in warm acclimatised and chronic cold-exposed birds
Melatonin from the pineal gland reduces the core body temperature at night - also facilitates sleep, which saves energy as they synchronise body temperature and metabolic rate when inactive
In avian species, which thyroid hormone changes and how, in response to changes in environmental temperature?
Plasma T3 - increases when colder
Plasma T3 - decreases when exposed to warmth
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