Homeostasis Flashcards
Homeostasis definition
process of coordinating physiology of an animal to maintain as constant internal environment as possible
Applicable to temperature and chemical systems
Why is temperature important
Affects rates of biochemical processes
Influences viscosity of cellular materials and fluids- warmer=more runny
Protein conformation
Temperature definition
Intensity of molecular motion
Heat definition
The energy contained in the entire system as a result of the motion of the molecules
Large objects at the same temperature have a greater amount of heat – more molecules
Heat interactions between homeothermic animals and the environment
generates heat as a waste product of its metabolism.
Some of the heat is stored so raising its body temperature above ambient.
Some heat radiates from the skin.
Some heat is lost as air next to the rabbit is heated and moves away via convection.
Some heat is lost by evaporation of water from the respiratory membranes or skin.
Some heat is conducted away through to the ground.
The environment also interacts with the rabbit – there is direct radiation from the sun and other surrounding structures and wind can affect rates of convection by increasing the loss of hot air above the skin.
Conduction
Transfer of heat through a material substance that is microscopically motionless
Convection
Transfer of heat between an object and a fluid or air directly in contact with the body’s surface that is macroscopically active
Radiation
Bodies emit electromagnetic radiation at infrared wavelengths
Evaporation
Latent heat of vaporisation removes heat from a body through evaporation of water from its surface
4 main ways of transferring heat
Conduction
Convection
Radiation
Evaporation
What is body surface temperature proportional to
Thickness and nature of outer layer of body and ambient (or environmental) temperature
Conduction - physics
Heat is transferred through microscopic movement of atoms and molecules
Movement of atoms will cause movement of adjacent atoms via interatomic collisions
Equivalent to diffusion of molecules
t2 – t1 = thermal gradient
Different materials have different conductivities, e.g. air has low conductivity so is a good insulator
Convection- physics
Heat is transferred through macroscopic movement of atoms and molecules
Movement of air or fluid molecules will cause movement of heat away from a surface
t2 – t1 = thermal gradient requires ambient fluid to be cooler
hc depends on many different aspects of the structure of the body and on the rate of fluid flow
Evaporation - physics
Water absorbs a lot of heat when it is converted from a liquid to a gas
Latent heat of vaporisation [evaporation] is ~2400 J/g
Evaporating water from the skin or other bodily surfaces is a very effective way of removing heat
Radiation - physics
All bodies above absolute temperature (0 K or -273°C) emit electromagnetic radiation in the infrared wavelengths at the speed of light
Jackrabbits can regulate blood flow to the vessels in their large pinnae
Act as radiators but also allows for convective heat loss
Total intensity of radiation increases as surface temperature increases
Pairs of bodies emit and receive thermal-radiation simultaneously
Can be absorbed or reflected depending on colour
A model animal
Rate of heat loss depends on degree of insulation in the outer layer of body
Body core temperature (TB) is achieved by combined effect of metabolic heat production, insulation and environmental temperature
High metabolic rate and good insulation can keep TB > TA for longer
Poikilothermic animals
unable to maintain a body temperature based on internal heat production. These can either keep their body temperature at the same temperature as their environment and have no need to thermoregulate. Other animals can raise their body temperature above ambient using various behavioural means.
Poikilothermy
animal’s body temperature is in equilibrium with the thermal conditions of the environment
Poikilothermy relates to variability in body temperature
Ectothermy
reflects the external sources of heat that determine body temperature
Homeothermy (endothermy)
animal’s body temperature is regulated to a relatively constant value by physiological means
Heterothermy
reflects an animal’s ability to regulate its core body temperature, or a portion of its body, by either temporal or regional variation and that body temperature varies
Which animals of Poikilothermic
Invertebrates
Lower vertebrates
Which animals are homeothermic
Birds
Mammals
Conformers
are in equilibrium with the ambient temperature but are at its mercy – any changes can affect their metabolic rate (which is temperature dependent). One solution is to find a niche in an environment that doesn’t change very much over time or at all. Therefore, deep-sea fish live under constant high pressure but water temperature may be cold but it doesn’t fluctuate.
Regulators
either use behavioural or metabolic mechanisms to maintain their body temperatures. The lizard basking on a rock uses heat radiated from the sun to warm its body and moves out of the sun when it is warm enough but its body temperature over the course of a day is not stable. Birds regulate body temperature at a constant level using metabolic sources of heat.
Eurythermal animals
Can tolerate a wide temperature range
Stenothermal animals
Can tolerate only a small range of temperatures
Thermal tolerance
Optimal evolutionary fitness is a function of life history and peak bodily performance is often at an optimal body temperature. High temperatures are typically more deleterious to performance than lower temperatures – within the Pejus range a small increase in temperature has a large adverse effect (compare with a decrease in temperature of the same magnitude). Thermal tolerance has both low and high critical temperatures that can adversely affect survival if they are crossed.
Which of the following organisms will have the greatest heat energy at 38°C: Capybara, Chinchilla, Harvest mouse, or Mara?
Capybara
What three ways can mammals lose heat by evaporation?
Cutaneous evaporation
Respiratory evaporation
True or false? Convection involves the loss of heat through direct contact with another surface.
True
Why do were consider a dormouse a heterotherm?
exhibit physiological mechanisms that allow them to modify their body temperature over a long period of time
Define a wide thermal tolerance?
Animals can tolerate a wide range of environmental temperatures
Different species have different thermal tolerances
Often reflect differences in enzyme activity
Different responses to changes in temperature
Acute
Chronic
Evolutionary
Acute responses of ectotherms
Temperature
Ectotherms derive heat from external sources and if they poikilothermic they will change temperature as the ambient temperature changes. This impacts on cell metabolism and body performance but changes in temperature produce an asymmetric curve around an optimal temperature. Reducing temperature slows performance and metabolic rate but small increases in temperature can have dramatic adverse effects on performance. These changes are characterized by curvilinear responses and a higher temperatures the effects can be abrupt.
What are acute physiological processes largely determined by
the physical properties of molecular interactions and the metabolic rate of an animal
How are acute responses quantified
Determining the Q10 value for a response
Q10 = RT/R(T-10)
RT is the rate at any given body temperature
R(T-10) is the rate at the temperature at a body temperature 10 °C lower
the slope of the regression line on a semi-logarithmic plot.
How are acute responses quantified
Determining the Q10 value for a response
Q10 = RT/R(T-10)
RT is the rate at any given body temperature
R(T-10) is the rate at the temperature at a body temperature 10 °C lower
the slope of the regression line on a semi-logarithmic plot.
Which physiological responses experience a breakpoint
Metabolism
Heart rate
Gill ventilation
What is LD50
Temperature where 50% of the population can survive
Proteins and temperature
Protein denaturation and coagulation- prevents eg enzyme activity
Proteins and temperature
Protein denaturation and coagulation- prevents eg enzyme activity
Why can different species withstand different changes in temperature
1) Different animal may have unique metabolic pathways that are critically sensitive to temperature
-May explain differences between species but diversity of habitat temperature means that variability in metabolic processes just isn’t observed
2) Small changes to amino acid sequences changes temperature sensitivity
-Enzymes in icefish may be denatured at 6ºC because they different in their amino acid profile to eurythermal fish that live at higher temperatures and are denatured at 30-35ºC
Arrhenius principle
Metabolic rate increases exponentially against temperature
Heat shock proteins
family of proteins that are produced by cells in response to exposure to physiologically stressful conditions (temperature, UV light, and during wound healing.
Perform chaperone function by stabilizing new proteins to ensure correct folding or by helping to refold proteins that were damaged by the cell stress
Q10 effect on proteins
Consider a simple metabolic pathway
X → Y Y → Z
Q10 = 1.7 Q10 = 3.0
As temperature increases the conversion of Y → Z will be almost twice as fast as the rate that it can be converted from X
Concentration of Y decreases and the production of Z decreases
Y may also be important in other metabolic processes, which then slow and perhaps fail
Lipids and temperature
Fluidity of lipids is temperature sensitive – as temperature increases they become more fluid, as it cools they can solidify
High temperatures cause lipids to become less organised
These changes in fluidity can affect the biochemical processes mediated by proteins embedded in the membrane
Low temperatures and lipids
As temperatures decrease there is a greater risk of ice crystal formation in cells that physically damage structures
Reduced temperatures may slow elements of key biochemical pathways and if the rate of reaction is too low then vital processes may be stopped
If axon conduction stops then this can affect important autonomic processes, such as breathing
Ironically, cold temperatures can delay death by slowing biochemical processes even after breathing or heart function have ceased.
Thermal selection and seasonality
Only species that are fixed to one location (e.g. sessile sponges or coral) lack any ability to control body temperature through some kind of behaviour
Water readily conducts heat and temperature can change on short or long term time periods
Simplest method of temperature control is to move to locations that are at the preferred body temperature
Temperature regulation in ectotherms and size
Body temperature rises as body mass increases
As animals grow their surface layers become better insulators so more metabolic heat is retained and a higher body temperature can be maintained- thermal inertia
Acute responses and behavioural changes
Behaviour
Posture
Increased surface area and colour to absorb sun’s radiation
Shading by vegetation
Short flights to increase convective heat losses
Albedo- lightening in colour eg frogs
Physiological changes in ectotherms when diving
Reduced heart rate
vasoconstriction
Physiological changes in ectotherms when too hot
Evaporative cooling via respiration
Distribution of blood
Chronic responses and temperature
Changes in metabolic rate
Evolutionary responses and temperature
Enzyme-substrate affinity depends on protein conformation, which in turn is affected by temperature
Differential expression of genes that produce heat shock proteins
Antifreeze proteins produced in liver and epidermis that absorbs ice crystals and prevents them growing- lowers freezing point of blood and minimises risk of ice nucleation . Accumulation of glycerol in blood lowering freezing point of lipids
Why is dark skin useful for an ectothermic amphibian?
Increased rate of heat absorption
Why does hypoxia cause the head temperature of bearded dragons to decrease?
Hypoxia induces gaping of the mouth that increases evaporation and cools the head
In terms of temperature, why are rock pools such a challenging environment?
Temperature of pools varies from 10-31 degrees
Pools can dry up
What is thought to enable Tegula brunnea to live at higher zones of a beach?
So in Tegula snails one species T. brunnea lives higher up the beachand is exposed to high ambient temperatures than the other species T. funebralis that lives further down the beach and is exposed for shorter periods. This choice of habitat is reflected in the differential expression of different heat shock proteins (HSP) – brunnea seems to express HSPs 38 & 70 more than funebralis. This is an evolutionary response that has allowed brunnea to live higher up the beach, which may confer other advantages to that species (e.g. reduced predation).
Homeotherms (endotherms)
Maintain a near constant high body temperature by utilising heat generated by metabolism
Thermoneutral zone
where the metabolic rate is unaffected by ambient temperature
Below a critical low ambient temperature metabolism increases because TB > TA
Above a critical ambient temperature TB < TA and so metabolism increases in a similar way to poikilotherms
Metabolic rate of vertebrates
Higher metabolic rates and higher body temperatures than lower vertebrates of equivalent mass
How does core body temperature vary across the day
Daily cycle
Diurnal species = higher during day
Nocturnal species = higher at night
Insulation in homeotherms
Helps retain metabolic heat within the core body allowing body temperature to rise
Fourier’s law of heat flow: M = C*(TB – TA)
M = metabolic rate and C = thermal conductance
Materials with a low thermal conductance are good insulators
Monitoring temperature in homeotherms
Determined using combination of peripheral and central temperature receptors
Skin receptors fire at a peak rate at particular temperatures
Cold receptors only sensitive at cooler temperatures
Warm receptors are deeper in dermis and only respond above 30 degrees
Thermosensitive neurones in CNS- especially pre-optic area of hypothalamus
Fever
Microbial infection stimulates fever- high body temperature but feel cold
Response to prostaglandins and thromboxanes (pyrogens) produced by white blood cells
Pyrogenes stimulate release of prostaglandin E2 that interacts with neurones in the pre-optic area to re-set the balance point
Higher body temperatures = faster clearances of micro-organisms
Acute responses in homeotherms
Changing level of insulation provided by air
Reducing or increasing blood flow to the periphery
Forced convection or conduction
Increased or reduced evaporative cooling
Increased metabolic heat production
Storage of heat
Piloerection
Modify thickness of fur/feather layer in response to cold
Shivering
Unsynchronised contraction and relaxation of skeletal muscle in high frequency rhythms to generate heat
Mediated by somatic nervous system
Brown adipose tissue in homeotherms
Mammals have brown adipose tissue that is stimulated by sympathetic nervous system to oxidise lipids to generate heat
Common in small, cold acclimatised mammals, hibernators and newborns
Vasodilation and vasoconstriction
Under hot conditions, vasodilation can allow blood to be shunted to the skin and lose heat via radiation, convection, and/or conduction
Under cold conditions vasoconstriction prevents blood from going to the skin and retains heat in the body core
First acute responses to temperature changes in homeotherms
Piloerection
Vasodilation/vasoconstriction
Acute responses to heat in homeotherms
Evaporative cooling (eg sweating, panting, gular flapping, saliva spreading)
Evolutionary responses in homeotherms
Countercurrent systems prevent heat loss in limbs
Respiratory turbinates
Respiratory turbinates
bony or cartilaginous structures in the nasal cavity of mammals and birds
They are simple or complex swirls or branched structures that are covered with a moist epithelium
Inspiration – air entering the nasal cavity is warmed as it passes over the epithelium – the turbinates cool
Expiration – air leaving the body passes over the cool turbinates which are then warmed and water vapour condenses on the epithelium
Birds expire air at 20ºC (core = 40ºC) saving 5% of energy expenditure
Rete mirabile
ball of blood capillaries located within a venous sinus that contains blood cooled by it coming from the nasal vein
can selectively cool blood going into the brain to minimise high temperature thermal stress
Thermal neutral zones and cold adapted mammals
Cold adapted mammals have wider thermal neutral zones and flatter responses of metabolic rate to cold temperatures
Heterothermy as an evolutionary response
many large moths and other insects have insulated (hairy) thoraxes and can rapidly contract their flight muscles without flapping their wings. This generates metabolic heat and raises muscle temperature and efficiency. This allows them to warm the muscles preferentially and so fly on relatively cold days.
The graph shows that these moths respond to colder air temperatures in a similar way to full homeotherms and can maintain high thoracic temperatures (aided by the insulation).
A similar system is often seen in very active, large oceanic fish, such as tuna. There are counter-current blood systems that retain heat the heat generated by muscle contraction within the muscles rather than it being sent to the skin where it would be lost. This increases muscle temperature and efficiency
Frost bite
caused by prolonged exposure to extreme cold
Lewis-Hunting reaction helps prevent this by having cycles of vasoconstriction and vasodilation to protect the extremities
Gigantothermy
leatherback turtles. These are amongst the largest of all modern reptiles and yet regularly visit cold seas. They are able to maintain a stable, relatively high temperature because of their large size, subcutaneous blubber and a counter-current heat exchanger in their flippers. They have different behaviours according to the water temperature, which they seem to use to ‘dump’ excessive metabolic heat generated during swimming.
Are body temperatures of birds generally higher or lower than in mammals?
Higher
Where would you find respiratory turbinates?
Nasal cavity
In the thermal neutral zone, what happens to basal metabolic rate?
Constant
Heat shock proteins
family of proteins produced by cells that are produced in response to physiological stressors (not just temperature). They serve to bind with other proteins in such a way to ensure that the protein configuration (shape) is maintained at temperatures where it could be changed and so not function. Peptide strands that combine to form 3D proteins are held together by the HSPs.
Response of amphibians to hot dry conditions
Lose water freely through cutaneous evaporation
Cannot produce hypertonic urine
Have limited tolerance to high temperatures
Not found in deserts?
Seasonal aestivation
Extended periods of time laying dormant
Diurnal retreat
Nocturnal behaviour
Aestivation
change in physiology often in relation to high temperatures (but not always). Many frogs that perform this feat create cocoons from their shed skin that they use to minimise water loss whilst they are in a burrow
Sandy soils – substrate remains friable and there is massive increase in water potential after rains
Heavier clay soils – substrate is denser and goes hard when dry
Cocoon formation can be a plastic response depending on water potential of soil
Amphibians can absorb water from the soil if osmotic balance is correct but process is complicated by water potentials of different soils
Aestivation- solute accumulation
Aestivating amphibians can accumulate molecules to increase osmotic pressure of body fluids
Urea is retained within tissues to reduce need to urinate and lose electrolytes
Aestivation- metabolic depression
Drops to 20-25% of SMR by 2-4 weeks of aestivation then remains stable
Extends survival time when using endogenous energy stores (lipids)
Response of reptiles to hot dry conditions
Bury themselves in wet mud
Aestivation for 4-5 months
Metabolic depression
Timing activity to coolest part of day
Response of fish to hot dr environments
Sequential expression of different categories of genes reflected severity of stress.
Regardless of acclimation temperature, mild stress = gene encoding heat shock protein 70 (HSP70) upregulated
Higher temperatures = the gene encoding the proteolytic protein ubiquitin (UBIQ) was upregulated
Extreme stress = a gene encoding cyclin-dependent kinase inhibitor 1B (CDKN1B) a protein involved in cell cycle arrest and apoptosis was upregulated
Desert tolerance in larks
Desert larks 43% lower basal metabolic rate and 27% lower total evaporative water loss
Heat tolerance in doves
Cold-acclimated birds use cutaneous water loss less than hot-acclimated doves, which rely less on respiratory water losses for cooling when challenged with high temperatures.
example of phenotypic plasticity in response to short-term acclimation
Hyperthermia as a response to heat stress
1) Greater difference between body and air temperature so “dry” heat loss is increased
2) Stored heat in body can be dissipated at other times when air temperatures are reduced
3) Increased Tb in thermoneutral zone reduces evaporative water loss
Cloacal evaporation
Evaporation via respiratory surfaces, the skin (cutaneous) or the cloaca
Some birds can use cloacal evaporation as part of their thermoregulation response to temperature stress
Response of heat-adapted bird species to low water availability
Sandgrouse (Pteroclididae) nest 50 km away from watering holes – reduced predation
Chicks potentially deprived of water but resolved by soaking of breast feathers by adults flying to drink
Toucan beak
Largest bill relative to body size of all birds
Used as controllable heat radiator that regulates heat distribution by modifying blood flow
How do mammals dissipate endogenous heat load
1) Increase thermal conductance to facilitate heat loss by conduction and convection
2) evaporative heat loss
3) Heat storage
Mammalian strategies to high temperature
Endurers – generally larger mammals
Avoiders – generally smaller mammals
Heat storage in mammals
allow body temperature to rise
In camels (Camelus dromedarius) heats storage depends on hydration status
Above 40°C there is an increase in the normal daily amplitude in body temperature fluctuation from 2 to 6°C
Heat gain in dehydrated camels is reduced but stored heat is greater
Metabolic depression – reduced food intake or mediated by reduced levels of circulating thyroid hormone
What is metabolic depression in mammals associated with
Reduced levels of thyroid hormone
Mammal avoiders
generally smaller mammals that avoid high daytime temperatures but if they are active in the day they adopt hyperthermy to store heat.
aestivation
Brought on food restriction, water restriction (or both)
Affects water losses
Body temperature tracks ambient temperature and oxygen consumption depressed
Can amphibians produce hypertonic urine?
No
Why are jackrabbits’ ears so large?
ears that can be infused with blood that increases the surface area for heat loss from the blood via radiation or convection but the air temperature has to be cooler than the body for this to work.
How does Crocodylus johnstoni deal with prolonged periods of high temperatures?
inhabit seasonally ephemeral water holes in wet-dry tropics of Australia
Dig burrows in river bank and stay 3-4 months
13% loss in body mass – no evidence of metabolic depression
Decrease in water loss from 40 to 9.3 mL kg-1 d-1
Size water pools in body decreased as body mass decreased
Cloacal urine osmolality, [K+], [Mg2+] all increased
Burrow was an adequate refuge and crocodiles can survive several months without access to water
Do primates have a rete mirabile?
No
What happens to metabolic rate during aestivation in amphibians?
Decreases
Responses of fish to potential freezing
Marine teleosts – body fluids freezing point is -0.8°C
Polar oceans temperature is -1.8°C
Produce antifreeze proteins in liver and epidermis that adsorb to ice crystals and prevent them growing
Lowers freezing point of blood and minimise risk of ice nucleation
Also accumulation of glycerol in the blood
Response of amphibians and reptiles to cold conditions
Winter dormancy
Aquatic – bottom of water bodies that often freeze at surface
Water has lower O2 capacity than air
Ice prevent air breathing so need to use skin or gills – aerobic activity leads to hypoxia
Metabolic depression due to Q10 effect and hypoxia – lower rates of energy reserves
Deep snow preclude photosynthetic production of oxygen in water
Tadpoles more tolerant to hypoxia
Response of reptiles to cold conditions
Lack antifreeze to depress the equilibrium freezing point of bodily fluids
Turtles remove active nucleating agents from bodily fluids (including bladder and gut)
Integument becomes a highly efficient barrier to the penetration of ice into body compartments from frozen soil.
Absence of a nucleating agent for ice crystals - bodily fluids remain in a supercooled, liquid state
Physiological challenges - increased reliance on anaerobic metabolism
Circulatory system is inhibited and then caused to shut down by declining temperature.
Alterations in acid/base status resulting from the accumulation of lactic acid may limit survival by supercooled turtles
Sublethal accumulations of lactate may affect behavior of turtles after the ground thaws in the spring
Cold tolerance in birds
Size matters – Compared to large species small birds have:
Higher metabolic rates
High surface area to volume ratio
Less insulation
Low temperatures lead to increased metabolic rate to increase heat production and maintain high body temperature
Bergman’s rule
Colder it gets – larger the body size so high latitude species should be bigger
Global patterns of body size in birds driven by interactions between the physiological demands of the environment, resource availability, species richness and taxonomic turnover among lineages
Adjustments to basal metabolic rate in cold in birds
In order to ensure high body temperatures are maintained birds have to adjust their basal metabolic rate to counter increased loss of heat at cold temperatures
Fourier’s equation: Metabolic rate = C x (Tb – Ta)
Where: C = thermal conductance of the body, Tb = body temperature and Ta = air temperature.
Shivering
Non-shivering thermogenesis
Digestion
Activity
Shivering in birds
Involuntary isotonic trembling of skeletal muscle that generates heat
Commences below critical low threshold – BMR cannot keep Tb stable
Muscles have to fatigue-resistant and most muscle fibres are not involved
Can increase BMR 5-fold (other physical activity = 15-20x BMR)
May be required for long period of time – titmice and the Goldcrest may need to shiver for days
Non-shivering thermogenesis
Involuntary heat production without muscle contraction
Found in mammals but perhaps not birds
Normally proton (H+) gradient across inner mitochondrial membrane used to generate ATP
Uncoupling protein (UCP) diverts protons into mitochondrial matrix so metabolic heat production is preserved
UCP activated by cold-exposure
Process confined to Brown Adipose tissue – high levels of UCP1
Birds do not have this system but do have avUCP – exact nature of mechanism is unknown
How does digestion increase body heat
Unavoidable heat production during digestion
Tawny owl – two feeding peaks (dusk & dawn)
Unavoidable heat production during digestion dependent on energy intake
~60% of thermoregulatory cost
Pigeons store food in crop and delay digestion until nightfall – contributes to heat generation
Behavioural changes of birds to cold
Food caching
Select roost site to minimise exposure to cold and wind
Roost communally – huddling together increases effective body mass
Emperor penguin incubation
Hibernation
Time inactive with depressed metabolic rate
It is also characterised by a periodic return to normal metabolic rates and processes.
It is a physiological response rather than a simple response to a lower ambient temperature as seen in amphibians and reptiles.
Torpor
Facultative body temperature reduction
And drop in basal metabolic rate
Mammalian endurers to cold weather - small mammals
Small mammals – problem of large surface area to volume ratio
Aggregate together in burrows – combined body mass when huddled improves heat retention and presence of animals can raise temperatures above that of the soil and ambient air
Burrow system under insulating layer of snow
Build nests for insulation
Hoard food
Mammalian endurers to cold- larger mammals
Large size = high thermal inertia
Medium to large mammals can increase cold tolerance
Acclimation of reindeer (Rangifer) allows the critical minimum air temperature for an increase in BMR to drop to -50°C from -30°C in the summer
Increase in insulation though thicker pelts – thicker underpelt produced by re-activation of secondary hair follicles dormant during summer
Mammalian responses to cold temperatures
Insulation via blubber in pinnipeds, sirenians & cetaceans
More effective than fur for deep dives or long-term submersion – pressure forces insulating air layer out
Regional heterothermy – counter-current heat exchanger for limbs
Useful in aquatic habitats (cetaceans) and terrestrial habitats (cold-acclimatized wolves [Canis lupus])
Decrease body size – requires less energy
Increase metabolic rate
Mammalian avoiders to cold weather
Migration
allow body temperature to fall close to ambient
“Hibernation” is a commonly used term for a period of dormancy during unfavourable climatic conditions.
Physiological process by which a homeothermic animal decreases its metabolic rate and allows its body temperature to drop to close that of the prevailing ambient air
Long-term hibernation – a form of controlled hypothermia
Observed in six orders of mammals: rodents (edible dormouse Glis glis and common dormouse Muscardinus avellanarius), bats, carnivores, insectivores (hedgehogs Erinaceus europaeus), marsupials & monotremes
Individuals seek refuge in a hibernaculum
Which 6 orders of mammals exhibit true hibernation
rodents (edible dormouse Glis glis and common dormouse Muscardinus avellanarius), bats, carnivores, insectivores (hedgehogs Erinaceus europaeus), marsupials & monotremes
True hibernation
And preparation
Involves periodic arousals where the metabolism returns to normal
animals become inactive with a decrease in heart rate, respiration and other bodily functions
Characterised by times when the individual is aroused and becomes active, albeit temporarily – reason for this is unknown
Hibernating mammals retain brown fat (NST) as adults- non-shivering thermogenesis
Lipids – particularly triacylglycerols are deposited in adipocytes in months leading up to hibernation
Temperature affects fluidity of long-chain FAs – polyunsaturated FAs (PUFAs) remain more chemically accessible at low temperatures than saturated fatty acids (SFAs)
Size of animals that hibernate
Most hibernating species body mass < 5kg
Beneficial effects on reduced metabolic rate decline with increasing body mass (bears are an exception)
Carnivorean lethargy
Fat is deposited during the autumn months and during winter badgers remain underground in their setts – this will be warmer than the outside. They effectively sleep and allow a drop in body temperature as their metabolic rate slows. However, this physiological state is not the same as that observed in species that exhibit true hibernation. They wake up on a regular basis and will be active for relatively long periods during winter.
Does shivering lower or raise the metabolic rate?
Raise
Is the surface area to volume ratio bigger in large or small birds?
Small
Is blubber a form of insulation?
Yes
How do fish in Antarctic waters use chemicals to stop them freezing?
Produce antifreeze proteins in liver and epidermis that adsorb to ice crystals and prevent them growing
Lowers freezing point of blood and minimise risk of ice nucleation
Where do Japanese macaques spend the winter month and why?
Japanese macaques (Macaca fuscata) will bathe in hot springs during winter unless they are being fed
Dominant females and offspring bathe more
Regional Heterothermy
counter-current heat exchanger for limbs
Useful in aquatic habitats (cetaceans) and terrestrial habitats (cold-acclimatized wolves [Canis lupus])
Decrease body size – requires less energy
Increase metabolic rate
caudal rete mirabile reduce heat loss
Migration
most mammals the distance travelled is proportional to body mass with the exception of bats, which are small in size but highly mobile and can migrate great distances (see graph).
Migration
most mammals the distance travelled is proportional to body mass with the exception of bats, which are small in size but highly mobile and can migrate great distances (see graph).
Migration
most mammals the distance travelled is proportional to body mass with the exception of bats, which are small in size but highly mobile and can migrate great distances (see graph).
