Unit 3: Thermoregulation Flashcards
(35 cards)
Example of the thermostat, how does it regulate temperature? What are the three parts of the thermostat that allows it to do this?
When temperature in the house is too low, it turns on and produces heat to warm the house. Once it’s too low, it turns off to allow the house to cool.
It does this through a negative feedback circuit:
Some physiological variable increases/decreases, which a sensor / receptor notices.
This sensor sends a signal to the integrator, which compares this value to the set point.
This then sends a signal to the effector if it is too far from that set point, and the effector is what CAUSES the change. Once the physiological variable changes back to its normal state, the sensor relays this to the integrator, which then turns the effector off.
What is homeostasis?
A dynamic process tightly regulated by an organism which changes its behaviour in order to keep all processes and traits in a certain liveable range. (Dynamic environment that has things to counteract those changes and keep it in a range, NOT ONE SPECIFIC VALUE!)
Or: “The regulation of an internal environment in the face of changes in the external environment.”
What are the four parts of a negative feedback loop for regulating a factor?
Give an example of this process using thermostat…
Stimulus: This is the changing factor that is to be regulated. When it increases or decreases from the desired value, then it will cause the rest of the circuit to turn on, which will work to counteract that change.
Sensor: This is the things that detects the change in this factor, which is the sensory neurons in the nervous system.
Integrator: This compares the current condition to the desired range, and hence will stimulate or inhibit the effector based on the changes that need to be made
Effector: This the physiological change that returns that specific factor to its desired range (like the motor neuron responding to a stimulus). This then acts as a negative feedback loop, because the stimulus moving away from its desired range activates the effector to force it back to its desired range.
For thermostat: Temperature in the building increases —> sensor picks up on this and sends the information to the integrator —> Integrator compares this value to the desired range it is set at, and if it is outside of that range, it will activate the effector —> The effector then turns off the thermostat to allow the room to cool down, and the sensor to stop being stimulated.
What is the difference between negative and positive feedback mechanisms? What are two examples of positive feedback?
Negative feedback mechanisms work to mitigate the effects of the environment, and hence prevent any changes that are occurring to bring it back to a set state.
Positive feedback mechanisms amplify any changes, by responding to that change with MORE change. Essentially one change sets off another, which sets of another and magnifies effects.
Example: Birth
Sensor: stretch receptors in the cervix detect that the baby is getting too large and pushing too much.
The integrator then takes this information and compares it to normal, and noticing that it is very different, it causes the pituitary gland to release oxytocin.
Effector: Oxytocin goes to the uterus and causes it to contract, putting more pressure on the baby and hence on the sensors and amplifying the signal. This makes the change much larger and continues growing until the baby is pushed out.
Another example: Melting arctic permafrost
As it melts, it releases methane which is a greenhouse gas that traps heat and causes global warming, which just leads to more melting of the permafrost and more methane being released.
What does Ta mean, and what does Tb mean? How do they affect each other?
Ta is ambient temperature, or the temperate of the outside/surrounding environment.
Tb is body temperature.
The outside temperature affects the inside temperature by conduction, and therefore if the inner temperature is to remain constant, then Ta determines how much energy is put into regulating that inner temperature. The more that Ta differs from Tb, the more energy that is put into keeping that Tb at its desired value. The closer they are, the less energy that has to be put in.
What are endotherms? How is heat generated in general, and how is heat exchanged within an animal? How can Tb be regulated then, utilizing all these heat exchange methods?
What is the rate for heat exchange called?
Endotherms are organisms that maintain a constant temperature regardless of the Ta, and hence they generate their heat from within (hence the “endo” term). Endotherms generate all their heat from metabolism (the sum of all their bodily reactions). This heat is then exchanged with the environment via conduction, convection, evaporation, and radiation from the sun, or infrared from the animal. Convection: works by bringing water molecules off the surface of the body and cooling the animal down. Essentially as the fluid moves (water or air) heat is conveyed. So heat is taken from the air and removed.
Conduction works by direct contact, which moves the heat energy stored within particles to other particles.
Evaporation: This is when heat is lost as water changes from a liquid to a gas, and this removes heat from the object.
Using all these methods of heat transfer, Tb can be regulated through various differnt methods of changing these rates of heat loss. Not all factors can be regulated, but lots of factors can be counteracted with other biological mechanisms.
The rate of heat exchange is called CONDUCTANCE.
How does conductance vary between large and small organisms? What is this due to?
Graph of Mass V.S. conductance looks like…
Large organisms have a smaller surface area to volume ratio, and so a lot of their body mass is not easily accessible from the outside. therefore, less heat exchange will occur, because a lot of that heat is trapped within their large volume that is no adequately balanced by surface area.
More surface area = more conductance
So less surface area per unit mass, then it has less conductance per unit mass and therefore loses less heat at a time. This can be good or bad depending on the environment the organism is living in.
Graph of mass v.s. Conductance will be a constant (linear) line, (on a manipulated y-axis). This is because as mass increase, SA:V ratio decreases, leasing to this inverse relationship. Increased volume is common for endotherms because if they are putting energy into increasing their metabolism in order to increase Tb, they don’t want that energy just being lost to the environment.
What is a homeotherm? What about a Heterotherm?
Homeotherm: This is an organism that maintains a constant body temperature independent of the ambient temperature. This inner temperature may differ between organisms, but for one organism it remains relatively constant over time (or else enzymes will begin to die off). This often goes along with endotherms, because they use metabolism to regulate their body temperature, in order to keep it at a constant value. Although Ta does effect this rate of metabolism, it doesn’t effect Tb itself (in general, however there may be slight fluctuations).
Heterotherm: This is an organism whose body temperature is dependent on Ta, and therefore it fluctuates and is not constant. This often goes along with an ectotherm, because ectotherms do not regulate their body temperature with metabolism, and instead use the environment to regulate their body temperature.
What is an endotherm? What about an ectotherm?
An endotherm uses metabolism to regulate its body temperature (Tb) because it can put in energy into this metabolism to produce heat. So when it is cold due to decreased Ta, it increases metabolic rates (because metabolism produces a lot of waste product (heat)). But when it is hot due to Ta, then it decreases the energy it puts into metabolism and hence generates less waste heat to cool down.
An ectotherm uses the environment to regulate its body heat, they do generate metabolic heat but they don’t keep it. therefore the energy they put into metabolism is much lower as they don’t need to produce their own heat. Instead they move to the sun to warm up and move to the shade to cool down — they still have to maintain a (maybe more loose) range of Tb or else their enzymes will denature. They do use energy to move based on the environment, but they don’t use nearly as much as endotherms use to produce their own heat.
Where is the most overlap on the plot of endotherms, ectotherms, heterotherms and homeotherm? Where is there a general absence of creatures and why? What is one example from each section?
The most overlap occurs in the Heterotherm and ectotherm section, as well as in the homeotherm and endotherm section (as these are the most energy efficient combination of traits). There are some that are homeotherms and ectotherms, as they can maintain a constant body temperature due to moving with the environmental Ta’s. However there is only one type of organism present in the endotherm Heterotherm section. This is because in general, if an organism is generating their own heat with metabolism, you are most likely going to keep a constant body temperature, or else what is the point of generating that heat? Most organisms that are heterotherms can survive on fluctuating Tb, and therefore it is not very energy efficient to use metabolism to regulate body temperature.
Endo-homeo: Mammals and birds
Ecto-homeo: Marine Fish and marine invertebrates
Ecto-hetero: terrestrial invertebrates and freshwater fish
Endo-hetero (rare): Mole-rats
What is regional heterothermy? What organisms is it used in?
This is when different parts of an organisms body are different temperatures. Usually, the core temperature is much warmer than the extremities because it needs to be to maintain a high metabolic rate. This occurs in ectothermic homeotherms, where they use outer temperatures to maintain their body temperature, but they also maintain a constant temperature. They use heat-exchange systems such as counter-current heat exchangers where the temperature of blood is equalized, allowing for less heat loss to the extremities. So the heat produced by metabolism can stay in the centre and not be lost as easily — though excessive heat is not produced for this purpose. Only the waste heat is collected. It does this by transferring heat from the warm blood leaving the muscles to the cold blood coming back from the surface, and therefore that heat is not able to escape easily. This keeps some systems warm that need to stay warm, whilst others (such as their heart) can fluctuate with the temperature of the water. These systems use mechanisms other than metabolism to maintain a constant body temperature and be a homeotherm, whilst also being an ectotherm.
So instead of the graph of water temperature vs muscle temperature being a constant increase, (usually a 1:1 ratio) it is more of a flat line.
Again, this is used in ECTOTHERMIC HOMEOTHERMS.
What are the consequences of being an endotherm?
It requires a lot of energy to maintain a constant body temperature because so much excess energy goes into producing your own heat and body temperature. Therefore you have less energy available in you energy budget for other things that may be just as important, so you have to spend more energy hunting for food.
Therefore, endotherms have a much higher resting metabolic rate in order to maintain that desired temperature, whereas ectotherms have a very small one in comparison. This is because ectotherms just move based on the environment and develop adaptations in response to the environment.
Why is temperature so important for metabolism?
Well as temperature increases, enzymatic function exponentially increases. This is because it increases the total energy of the system and hence the total movement of all particles in a system, leading to more collisions and hence a larger number of effective collisions that lead to a reaction (or more collisions with enzymes). In addition, it increases the number of effective collisions by increasing the ratio of effective: ineffective collisions, since all particles have more energy and so a larger proportion will be able to overcome activation energy. These two combined exponential increase metabolic activity as temperature increases, until the maximum/optimum temperature is reached. Then this metabolic activity quickly drops off, due to the denaturing of enzymes that cannot survive in these high temperatures, as the molecules are too excited and break apart.
So temp up, activities will occur faster and more efficiently, until it becomes too hot and those enzymes can no longer function. BECAUSE ENZYMES MAKE UP METABOLISM.
Because enzymes depend on temperature, and metabolism depends on enzymes, enzymatic function drives metabolism which in turn drives performance.
As ambient temperature increases, how does body temperature increase for both ectotherms and endotherms?
For endotherms: At first, there is a quick increase in body temperature, because at too low of an environmental temperature, inner body temperature becomes too low for survival since enzymes can’t function and therefore temperature will not be maintained in the optimum since metabolism cannot occur efficiently (hypothermia). The same thing happens at the extreme, body temperature drastically increases outside of the desired constant, leading to death of the organism because enzymes are denatured and can no longer regulate body temperature.
For ectotherms: As environmental temperature increases, body temperature increases linearly, and this is why the creatures need to move to the shade or cooler areas to cool down at too high a temperature. This results in a linear upwards line, indicating a 1:1 relationship between body and ambient temperature.
Homeothermic endotherm response to temperature graph, and what are the different parts of the graph?
In this graph, at a very low Ta, the creature will be in hypothermy, where it is much too cold and molecular motion is much to slow to survive without intervention. therefore metabolic rate greatly increases in order to maintain function and heat. This is done through shivering, blood vessel constriction, etc. Then as Ta increases, RMR decreases as Ta approaches desired Tb, since less energy is required to bring it into that natural zone. Then once Ta reaches the range of temperatures that Tb should be, RMR is extremely low, and this is at basal metabolic rate, which is the amount of energy needed to breathe, maintain your heartbeat, keep body temperate normal, and maintain organ functions. Since Ta is already close enough to Tb, maintaining body temperature is not needed and this allows for BMR to occur. This spot is called THERMAL NEUTRAL ZONE and is where maximum performance of the organism can occur because the energy budget has a lot more space for other things rather then just maintaining body temperature.
The slope of the line depends on conductance, or the rate of heat transfer. Larger conductance is a steeper slope because the rate of heat transfer is much larger.
Then when the temperate gets too hot, we have to expend energy to sweat or pant in order to cool down, which once again costs energy and takes away from other processes, leading to less efficiency within the animal. This is called hyperthermy.
THE AMOUNT OF ENERGY NEEDING TO BE EXPENDED IS BASED ON THE DIFFERENCE IN AMBIENT TEMPERATURE TO TNZ. AS Ta APPROACHES TNZ, LESS ENERGY HAS TO BE PUT INTO MAINTAINING THE DESIRED INSIDE TEMPERATURE (REQUIRED FOR ENZYMES TO FUNCTION PROPERLY) AND THEREFORE LESS ENERGY HAS TO BE EXPENDED IN THIS AREA AND THE ORGANISMS CAN BE MORE EFFICIENT IN OTHER AREAS.
What are some short term strategies that can be used to regulate temperature outside the thermal neutral zone? (For below and above).
Below TNZ:
-Shivering
-Vasoconstriction (less blood to periphery and hence heat loss to environment due to a decrease in surface area)
-Piloerection (increasing depth of fur)
-Decreasing overall surface area (curl up or layer up to decrease exposure)
-Decrease exposure (huddling or burrowing)
Above TNZ:
-Panting (to release heat through conduction and convection)
-Vasodilation (increase surface area and transfer of heat to environment)
-Sweating (evaporation brings heat with it because energy has to be absorbed to go from a liquid to a gas)
-Increasing surface area and increasing exposure to environment
-But decreasing exposure to the sun
These are all strategies that can occur pretty instantly during a change in Ta, and these occur for both ectotherms and endotherms — though it is most important for ectotherms.
Growing fur, adding fat, shedding and changing colour are all more long term strategies that cannot be regulated immediately.
What are some specific adaptations that arctic and tropical endotherms have?
They have specific adaptations that change their conductance. For arctic animals, they have low conductance in order to retain heat, (less heat transfer per unit time), and to maintain these strategies RMR must increase.
For tropical animals, they must increase conductance to increase transfer of heat and hence heat loss.
In general, as Ta increases, the rate of decrease of RMR is much larger for tropical animals in comparison to arctic animals.
How do Heterothermic ectotherms respond to changing temperature? Do they have a thermal neutral zone?
Heterothermic ectotherms are organisms whose body temperature varies based on Ta, and they are able to survive on this because their organs are adapted to changing temperatures.
So at very low Ta’s, the organisms go into hypothermia as well, where enzymes simply do not have enough energy to carry out their reactions and molecules are not moving with enough speed to collide often enough for effective reactions to occur.
Then as Ta’s increase, the metabolic rates increase to a rate that can sustain life, however, the reactions are still not very efficient. This stage is called lethargy, because enzymes have less energy, particles collide less, and hence less reactions occur. So activity still occurs but it is much less then normal.
Then Ta gets to a point where the temperature is in the optimal zone for enzymes and proteins, and therefore the animal is able to be the most efficient and active, and this is the “activity” zone which is a sweet spot. Ectotherms will move in response to changing temperatures to absorb more sunlight if cold or go in the shade if hot, in order to stay within this optimal temperature range. Then as Ta gets much too high, enzymes begin to degrade and this is hyperthermia, where no reactions can occur and hence the organism dies.
They do NOT have a thermal neutral zone because this zone is talking about when the environment is similar in temperature to the optimal temperature required for that organisms enzymes, and therefore this is the point at which RMR turns into BMR since no excess energy has to be put into metabolism in order to keep the Tb within that optimal zone. Instead the “activity” zone is essentially where their TNZ is, however they do not regulate their own heat with metabolism so we cannot really call it that.
So essentially, their Tb changes with the Ta and the only thing they can do about it is change location to change the Ta around them.
What behavioural mechanisms can animals use to minimize energy expenditure due to temperature? (usually by increased energy expenditure due to increased RMR to stay warm, but can also include sweating to stay cool). Is this used by ectotherms, endotherms, or both?
They can move to warmer or cooler place in order to optimize heat exchange (conductance) with the environment and attain an ideal body temperature.
-Change exposure (seek/avoid sun or wind) (burrow)
-Group to decrease SA exposed and maintain heat
-Migrate
-Dormancy (hide in a cave and avoid the cold altogether so that no energy has to be put into keeping your body warm through metabolism)
These methods are used by both endotherms and ectotherms, because if you move somewhere to change Ta around you, then metabolism doesn’t have to work as hard to maintain optimal body temperature for endotherms. However, this has the largest effect on ectotherms, and is actually the main factor allowing them to maintain a constant body temperature.
Although very high Ta’s can damage enzymes, how do moderately high Ta’s effect metabolic rate?
Well as Ta increases, so does Tb. And if there is more energy available within particles, as well as more collisions occurring overall, then total energy budget can increase, and hence metabolic rate can increase without effecting any other processes. Therefore, because there is more energy available to do work, more work can be done at once, allowing organisms to be much more efficient. So at slightly elevated Ta’s, yes more energy must be put into cooling mechanisms, but total energy budget overall will increase and so organisms are still quite efficient.
Which type of organism can maintain high levels of activity over the greatest range of Ta’s?
A) Heterothermic endotherms
B) Heterothermic ectotherms
C) Homeothermic endotherms
D) Homeothermic ectotherms
C) Homeothermic endotherms. This is because they use metabolic rate to regulate their own temperature, AND they try to maintain a relatively constant Tb. Therefore, over very large variances in Ta, Tb can remain relatively constant (especially when in thermal neutral zone).
Heterothermic organisms have a changing body temperature with the environment. And homeothermic ectotherms will have fluctuations with Ta, especially to parts of their body that are maybe not regulated (regional heterothermy). Therefore they will not always maintain a constant body temperature because sometimes it is too hard to move somewhere that will regulate that temperature.
What is torpor and why is it used?
Torpor is a dormancy strategy that only occurs over a short amount of time (such as over a portion of the day). Its purpose is to drastically reduce RMR and Tb in order to not need to take in as much energy. Since endotherms use metabolism to regulate Tb, Tb will decrease as Tb does. This occurs in mostly small mammals, and occurs over around 6-8 hours with a reduction in Tb by about 10 degrees Celsius.
Especially useful in winter when food is scarce and so it is best to use torpor so less food needs to be taken in and the organism can survive.
What is hibernation and why is it used?
Hibernation is a long term version of torpor, resulting in a much larger drop in Tb and hence a larger drop in RMR then with torpor. This is because they are inactive for a longer time and so body temperature is able to drop more before it needs to rise again. Again, this usually occurs in smaller mammals, because a large SA:V ratio makes it easier to quickly bring Tb up and down.
To do hibernation, lipids are stored before hibernation so that there are large amounts of energy sources available to metabolize when sleeping.
Hibernation can be for weeks or month depending.
And when they need to get up to release toxic waste, this will occur for 1-2 days periodically. This arousal requires a LOT of energy, which is why the SA:V ratio needs to be large to absorb as much energy from the environment as possible.
When in hibernation, Tb drops to almost Ta.
What is the differnce between hibernation and a winter sleep? Why can’t hibernation be used in larger animals?
A winter sleep is when Tb still stays relatively high in comparison to Ta, and this sleep occurs for a couple days at a time, in between which the animal will wake up for a short period, excrete waste, and then go back to sleep.
Because Tb does not drop as far, this is not hibernation. But it also occurs for longer then torpor, so it can’t be torpor either. This is why it is called a winter sleep instead.
Because bears have a low surface area to volume ratio, they can conserve heat much more easily, and therefore Tb doesn’t have to drop as far for their RMR to be sufficiently decreased. Their RMR may be as decreased as an animal in hibernation, and yet their Tb has not dropped as far because they can maintain heat easier without having to put energy into it.
