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 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
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 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
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.
