Energy Balance (B) Part 2 Flashcards
Heat loss is a linear function of Tb-Ta which occurs when the animal’s ability to reduce _____ is exceeded. What happens to the metabolic rate in the cold?
Heat loss is a linear function of Tb-Ta which occurs when the animal’s ability to reduce CAPACITANCE is exceeded (increase capacitance). MR increases. The RMR increases as temperature decreases
How does an increase in insulation affect the TNZ? In an MR vs temp graph, what does a shallow slope indicate?
an increase in insulation extends the TNZ downwards to a lower Ta ( look at flat portion). A shallowed slope indivcates a lower requirement to increase MR in cold temps.
recall that the SLOPE of an MR vs Temp graph is CONDUCTANCE
this line of the winter time curve should have a LOWER tnz, graph error
2 evolutionary adaptations to the cld
1) increase insulation or decrease conductance in order to extend the thermoneutral zone of the animal downwards to a lower Ta.
2) Adaptation of the mammal size with latitude.
- get larger with colder temperatures (the more north you go). THis only occurs within species really.
- low surface area: volume ratio.
Bergmann’s Rule
involves body size and conductance. If all else is equal, small individuals have higher rates of heat loss.
- animals can get larger with increase latitude because the large volume and small surface area prevents additional heat loss.
- SA DOESNT EXPLAIN BMR SCALING BUT IT DOES INFLUENCE THERMOREGULATION.
3 broad ways endotherms thermoregulate to the cold
1) heat conservation
2) heat production
3) gaining external heat via behavior (ex/ basking, or moving to an A/C environment
methods that endotherms can employ to conserve heat
1) fur/feathers/goosebumps trap air
2) blubber insulation
3) vasomotor adaptations (see part 1 energy balance pack)
4) larger size at higher latitude (bergmanns rule)
5) countercurrent heat exchange. (which is basically another vasomotor adaptation aha)
explain the counter current heat exchanges in long legged birds for heat conservation
counter current exchange systems are seen in long legged birds because they have poor insulation. Adjacent blood vessels called the RETE MIRABILE run opposite directions to birng in warm air and remove colder air.
Heat moves in the following way: Warm core blood moves out the arteries toward the cold peripheral tissue. In the rete, it encounters cold blood from that periphery. By conduction, the heat moves into the cold vein and thus returns to the core. The venous blood leaving the rete is thus nearly at the temperature of the periphery so that little core heat is lost.
In this pic: A rete exchanger in the leg of a stork at an air temperature of 12°C and floor temperature of 20°C, showing body temperature (plotted line) along the leg. The inset shows the principle of countercurrent exchange in a rete.
explain the countercurrent heat exchanger system seen in penguins
Penguins havve a A venae comitantes rete, with two or more anastomosing veins being heated by surrounding a central artery (shown for a penguin flipper).
Explain the counter current exchange system in a whale tail
A whale tail has a centralized rete, with one central large artery surrounded by many separate, small veins (shown for fluke of a whale).
3 methods that help endotherms produce heat
1) idling speed
2) shivering thermogenesis
3) non-shivering thermogenesis
Why do endotherms produce so much heat in general?
we have a higher BMR that requires our processes to function at a faster rate.
the actual mechanism is because of LEAKY CELL MEMBRANES: maintaining metabolic processes with a leaky membrane requires more work by Na+/K+ atpase to constantly work to keep ion concentrations normal. This requires causes more heat to be produced/
and endothermic BMR= 5-20 times an ectotherm’s BMR of the same mass.
How does shivering thermogenesis work to produce heat?
shivering thermogenesis is the excitation of antagonistic skeletal muscle resulting in uncontrolled contractions. it isn’t efficient because there is no external work being performed while these muscles are moving.
heat is produced because of the ATP being hydrolysed.
how does non-shivering thermogenesis work
non-shivering thermogenesis results of burning of lipid in specialized Brown Adipose Tissue
why is brown adipose tissue brown
many large specialized mitochondria with high blood supplies
locations of brown adipose tissue
subscapular regions: heart, head, kidneys
Explain the rat experiment that tested non shivering thermogenesis
experimenters took warm-acclimated rats in a cold room. THey shivered like crazy. When injected with curare, they could no longer shiver but they were still able to defend a Tb. Therefore, there is an internal mechanism that also provides some heat production.
Also, over a few weeks, the amount of shivering decreased. this indicates that they were ablet o create brown adipose tissue to maintain body temperature.
Why do humans stop shivering after being exposed to chronically lower temperatures for a couple weeks?
weve undergone acclimation by increased brown adipose tissue recruitment
explain the mechanism behind how brown adipose tissue produces heat.
When activated by cold or diet via a nerve that releases norepinephrine, the uncoupling protein (UCP) called thermogenin in the brown adipose tissue cells opens and allows protons (H+) to pass through the inner mitochondrial membrane. This dissipates the proton gradient as heat without making ATP. Heat is transferred to blood supply then to brain, heart, kidneys etc.
NE binds to beta receptors, resulting in the production of cAMP, which activaes lipase. this hydrolyzes triglycerides stored in brown adipose tissue, and these free fatty acids fuel mitochondrial oxydation
Facultative heterothermy is sort a way for endotherms to still regulate their body temperature instead of working to maintain it at a specific point. what are examples of facultative heterothermy.
an example is facultative hypotheria – ie/ torpor or hibernation
What is torpor?
a method employed by facultative heterotherms that result in a drop in Tb to save energy. this is a very frequent process- often daily. Seen in bats, rodents etc.
when in torpor, the animals can defend a new, lower tb.
graph: orange spike should be metabolic rate, not Tb. Tb doesn’t spike when you get out of torpor.
Draw how the Mr vs ambien temp graph differs when an animal is in torpor
what is hibernation? Are there periods of arousal during hibernation even when the metabolic rate drops?
a profound and SEASONAL (longer than torpor bouts) drop in Tb to just over the ambient temperature. results in a drop in metabolic rate of up to 95%. Hibernators must store up large amounts of unsaturated fats (which do not turn hard like butter at cold body temperatures) to serve as energy reserves.
There are periodic arousal bouts during hibernation, but shivering and non-shivering thermogenesis powers them. the blue lines on the graph indicate the bouts of periodic arousal
differences between large and small animal hibernations
- true hibernators are small animals. bears cannot truly hibernate because they can’t get their body temps to lower enough (because of the low SA:vol ratio)
the large mass is also expensive to rewarm afterwards. they cannot periodically arouse if they were to drop to Ta temp levels. But, this slight decrease in Tb still saves energy
3 costs of torpor
1) reproduction. MR lowers so much that female animals cannot lactate. there is also delayed parturition (delyaed birth), and slower offspring growth
2) risk of predation
3) physiological costs. sleep deprivation, accumulation of nitrogenous wastes.
ex chipmunks do not increase fat stores, they build food stores. Chipmunks with extra food remained NORMOTHERMIC more often (less torpor). They may have not slept much because of nitrogenous waste accumulation.
2 strategies for extreme cold
1) freeze tolerance
2) freeze avoidance
2 methods bodies have for freeze tolerance.
freezing is bad because it causes dehydration and crystallization.Ice crystals form in the ECF and reduce the concentration of water, resulting in water leaving the ICF, causing cellular dehydration
1) ice nucleaors like phospholipids and calcium salts ensure prevent freezing by aggregating in the ECF and reducing the ability to form large “normal” ice crystals in the ECF, thus preventing the movement of water outside of the cell and preventing dehydration
2) intracellular solutes from liver glycogen stores are seen 450 times the normal in wood frogs. this is an anti-freeze by lowering the freezing point through simple colligative properties, and creates am osmotic gradient that prevents dehydration: compatible cryoprotectant. The cryoprotectant acts as an osmolyte to help keep the cells in osmotic balance with the increasing osmotic pressure in the ECF. prevents water from leaving the cell to form ice crystals.
2 strategies for freeze avoidance
1) antifreeze proteins or glycoproteins
2) super cooling
how to antifreeze proteins work in order to avoid freezing?
These proteins are effective at much lower concentrations than the compatible cryoprotectants. They generally contain very hydrophilic amino acids and sugar side chains that are thought to bind to growing ice crystals and thus prevent their growth.
this is seen in numerous species of fish, insects and plants.
What is super cooling and how does it aid in freeze avoidance? Why is it dangerous?
Supercooling is a state of water in which the temperature is well below the freezing point but there is no nucleation site to begin ice formation. Supercooling is a dangerous strategy, however, because any encounter with external ice can trigger a catastrophically rapid crystallization of body fluids.
Why does heat loss become more difficult when Ta decreases?
because of the reduced gradient.
how to camels exhibit heat tolerance?
They allow their body temp to rise during the day and allows it to decrease at night. With a 6 degree temp fluctuation, a 500kg camen saves approx 4.5 L water a day not maintaining a constant body temperature. it also has the ability to store urea and avoid necesssity to urinate.
3 methods of endothermic regulation in warm environments
1) tolerance; temporal heterothermy
2) heat exchangers
3) active heat loss
how do heat exchangers work in ungulates?
1) they have a temporal countercurrent system in the nasal cavity which cools arterial blood and conserves water.
The inhalation of drier air from the external environment evaporates this water produced by a prior condensation of air and cools the surface of the maxilloturbinal surface in the nose in preparation for the next breath cycle.
In a temporal countercurrent exchanger, the opposing flows of a fluid are separated in time (using one tube) rather than in
space (using two separate tubes). Mammals on average reclaim as much as 45% of the water (and its heat content) from the exhaled air
2) The carotid rete COUNTER CURRENT EXCHANGER that runs parallel to cool venous drainage from the nasal cavity and skin.
Advantages of heat exchangers in endotherms
1) cools brain
2) prevents brain from shutting down muscles
3) prevents brain from activating evaporation and prevents water loss.
What happens to metabolic rate before Ta= Tb? How does this occur? (active heat loss)
at the upper end of the thermoneutral zone, beofre Ta= Tb, MR BEGINS TO INCREASE. If the heat is not lost, the Tb will rise (bad), so heat must be lost before Ta exceeds Tb.
This occurs by INCREASING CAPACITANCE (reducing insulation) Q(heatloss)= C(Tb-ta)
Endotherms have at least two evaporation mechanisms specifically adapted for thermoregulation: ____ ____ and “insensible” _____ _____through the skin
Respiratory panting and insensible CURTANEOUS LOSS through the skin
In birds, panting is supplemented with gullar fluttering, which is:
rapid fluttering of the well-vascularized esophageal region. This rhythmic inflation of the hyoid apparatus is termed gular fluttering.
How is respiratory alkolosis avoided in animals that pant? Wouldn’t this rapid breathing result in decreasing CO2 in the blood?
respiratory alklosis is avoided in part by the rapid and VERY shallow breathing. It uses the DEAD SPACE of the respiratory tract.
Panting involves inhaling through the nose and ehaling through the mouth, where condensation is evaporated from the tongue, and allows for the one-way flow over non-exchange surfaces, so no blood O2/CO2 concentration imbalances occur
the resonant frequency of the thorax is alos limited, minimizing muscular activity.
principle means of thermoregulation in ectotherms
behavior. ectothermic individuals select a desired ambient temperature that their body temp works functionally at. this implies the existence of temperature-sensitive neurons in the brain. There are also some cardiovascular adaptations to obtain/retain heat, but behavior modification is the primary source.
How do juvenile sockeye salmons thermoregulate?
they implement diel migration. In order to prevent predation when the juveniles are feeding on surface insects, the optimize forgaing time that gives them enough light to see bugs but prevents them from being seen by a bird. During dawn: they feed at the surface, and in the day, the LOWER THEIR MR and go to the bottom (LOW TEMP) of the thermocline to chill out of sight from predators. at night, they rest above the thermocline in order to have optimum growing temperature.
how do fish employ aspects of regional heterothermy (heating only certain organs)?
teleosts are able to maintain a somewhat constant temperature becaused of evolved endothermy, primarily in their red or aerobic swimming muscles. These animals migrate over long distances, swimming continuously with these muscles and generating constant heat output. But it is not enough to heat the entire body, because too much heat is lost at the gills through CONDUCTION (gills are a limiting factor). A countercurrent rete system between the aerobic muscle and the gills prevents most of the loss
How do insects exhibit endothermy?
during preflight warm-up, some species shiver their flight muscles before takeoff. During flight they can keep their thoraxes at relatively constant and high temperatures by controlling hemolymph flow between the thorax and abdomen, which are connected by countercurrent flow channels . The abdomen has a thin ventral surface, the thermal window, through which excessive heat can be lost.
Some insects may also keep warm because of chitin for insulation
what is heterothermy and what categories are heterothermy are there?
In addition to birds and mammals, many other animals (exhibit some form of endothermy, but unlike birds and mammals, they do not heat all their cores. Furthermore, some animals including many small birds and mammals cannot maintain high core tem- peratures continuously, because of their high ratios of sur- face area to volume, coupled with insufficient food supply. Such animals are called heterotherms, falling into two broad categories: regional and temporal.
What is regional heterothermy? Temporal heterothermy?
Regional heterothermy occurs in endothermic animals that heat only certain organs or body regions, not their entire bodies.
Temporal heterothermy is manifested in endotherms that regularly shift from a regulated high body temperature to a low body temperature, most commonly in daily torpor and seasonal hibernation.
reptiles contain a “thermostat” in their ____ , like in all other vertebrates
hypothalamis
How do reptiles gain heat?
solar radiation, other environmental sources like rocks, muscle activity
explain how a python has similar cardiovascular adaptations to many endotherms in terms of compensatory heat retention
shivering has evolved in pythons. This allows for the Tb to increase in order to incubate eggs. Therefore, like many endotherms, the metabolic rate of a python actually goes UP when the ambient temperature FALLS
this graph shows that as temp decreases, the number of contractions and the body temperature increases when brooding.
how is thermoregulation in repitles correlated with reproduction?
during non breeding, they are pretty ectothermic, Tb= Ta.
When they’re brooding, there is an increase in heat production, like in pythons, Tb may exceed Ta for some species.
How is heat lost in reptiles?
1) avoidance behavior
2) cardiovascular activity
3) gular flutter (like in birds, allows for evaporative heat loss like panting)
4) habitat features: radiation, conduction, convection.
advantages to thermoregulatory capabilities
1) avoidance of lethal temperatures
2) greater activity at low ta than conforming Tb’s would permit.
3) maintain optimum Tb for efficient enzyme performance.
4) different species may occupy different preferred temperaturees, allows for proper resource partitioning! Occupation of a variety of different ecological niches can reduce competition.
How does the dipsosaurus dorsalis have thermoregulatory capabilities that allows it to live in high temps where theres not much competition
These lizards are able to remain active in high temperatures, and can even tolerate 47 degree temperatures because of special HEAT SHOCK PROTEINS. The 3 D strcuture of proteins help maintain enzyme function.
How do heatshock proteins (seen in dipsosaurus dorsalis lizard) allow for enhanced thermoregulatory capabilities?
heatshock protein dissociates and bind to proteins to hold it together to prevent dissociation of other proteins. A portion of the heatshock proteim, HSF1, acts as transcription factor and producs even more HSPs
what are similar mechanisms reptiles have to endotherms (even though they’re functionally ectothermic) in terms of thermoregulation
1) set point regulated in hypothalamus
2) cardiovascular heat gain/retention/loss mechanisms
3) evaporative cooling via gullar flutter
4) capacity for endothermy (limited) ex/ python shivering
limitations in thermoregulation in reptiles
1) insulation
2) comparable capacity for aerobic metabolism– same costs and benefits as mammals and birds.
Do amphibians have any endothermic capacity at all?
they are basically completley ectothermic becaues of cutaneous respiration and water dependence. The have even less insulative skin and water loss, which LIMITS AEROBIC METABOLISM
the aerobic capacity model for the evolution of endothermy
the idea that there was selection pressure for a bunch of traits that allowed specieis to run faster and facilitated the production of heat-generating structures and the increased ability to do aerobic respiration.
- increased aerobic capacity was a result and allowed subsequent increase in locomotion
the parental care model of the evolution of endothermy
the idea that the increased rate of offspring development at higher temperature was beneficial.
What is the noctunal bottleneck hypothesis for the evolution of endothermy in MAMMALS
the idea that mammals and their therapsid ancestors were around at night when ammales were hunted by dinosaurs. They hi in burrows during day time and came out at night when it was cold. it was beneficial to have HEAT GENERATING MECHANISMS. Even today, most extant mammals are still small and nocturnal. Most mammals can also see better at night than birds or reptiles.
Fungal avoidance hypothesis
fungi thrive at lower temperature. Upregulating temp via endothermy prevents fungal growth.
the hypothalamus typically controls thermoregulatory proceses. the ____hhypothalamus is activated by the cold, and the ____ hypothalamus is activated by warm temperatures.
the hypothalamus typically controls thermoregulatory proceses. the POSTERIOR hhypothalamus is activated by the cold, and the ANTERIOR hypothalamus is activated by warm temperatures.
two timescales for the “evolution” of thermal compensatory mechanisms
1) acclimatization (within lifetime)
2) adaptation (evolutionary time)
two critical macromolecules involved in thermal compensation
1) lipids (esp for membranes
2) proteins
membrane lipids are held together by -___ interactions.
hydrophobic interactions.
what is the homeoviscous adaptation and give the 3 examples
physiological systems used to maintain similar levels of membrane viscosity.
1) incrase unsaturation of phospholipids to increase membrane fluidity. hlps with cold temperatures.
- this is seenin hibernator diets: they eat polyunsaturated fats because their membranes are kept fluid in the cold
2) de novo synthesis: replace whole regions of membrane
3) in situ synthesis: enzymes modify individual phospholipids
How can membranes be altered to accound for different temps?
1) shorter chain lenghts = higher fluidity. the longer the phospholipid tails, the more interactions between the tails are possible and the less fluid the membrane will be
2) unsaturation = higher fluidity
3) replacing phosphatidylcholine for phosphatidyletholamine
what is Kcat
how fast an enzyme can catalyse a reaction
Enzymes of animals with warm bodies, such as mammals, have relatively _____ (low kcat) enzymes, whereas cold-bodied animals have _____(high kcat) enzymes.
Enzymes of animals with warm bod- ies, such as mammals, have relatively inefficient (low kcat) enzymes, whereas cold-bodied animals have faster (high kcat) enzymes.
explain the effects of temperature on LDH and its Kcat in different species.
LDH is the final enzyme of anaerobic glycolysis, catalyzing the conversion of pyruvate and NADH to lactate and NAD+. As shownKcat of LDHs is inversely related to an animal’s Kcat average body temperature. This is a tradeoff between stability and reaction rate.
- high temp endotherms have very stable LDH to resist denaturation.
- low temp ectotherms don’t need as stable LDH because the risk of denaturation is lower.
Warm-adapted LDHs have relatively stiff loops, rigid enough to resist denaturation at higher temperatures. But they are too inflexible to work at cold temperatures. Cold-adapted LDHs have relatively loose loops, able to open and close well in the cold. But they lose their structure more easily at higher temperatures.
Note: biomolecular temperature effects summary:
1) membrane and storage lipids
- fluidity at low temps can occur readily within individuals with hhomeoviscous adaptations
2) protein and enzyme changes
- more likely to occur over evolutionary time and expression can increase reaction rates.
How are fevers caused?
in response to microbial invasion, certain white blood cells release a pyrogen (espe- cially interleukin-1, IL-1), which acts on the hypothalamic thermoregulatory center to raise the setting of the thermostat (see p. 469). The hypothalamus now maintains the temperature at the new set level instead of maintaining normal body temperature.
some gram-negative (able to be treated with antibiotics) bacteria have exogenous pyrogen (endotoxin) on the cell surface to also induce a fever.
the higher Tb may stimulate leukocyte sythesis and phagocytosis. May interfere with bacterial reproduction.
difference between fever and hyperthermia
fever is a deliberate attempt to get rid of infection by purposely increasing Tb. this high tb may stimulated leukocyte synthesis and phagocytosis.
Hyperthermia is an unintentional displacement of Tb from a fixed set point
