Thermoregulation Flashcards
What is the coldest recorded temp on Earth?
-129 F in Antarctica
What is the hottest recorded temp on Earth?
136 F in Libya
What are two sources of heat into the body and one source of heat out?
IN: Metabolic Heat, Environmental Heat
OUT: Environmental Loss
Name two different classes of animals by response to changes in environment temperature (with short description)
Homeotherms: Animals that are capable of maintaining the same body temperature with changing environment
Poikilotherms: Animals that allow their body temperatures to fluctuate with changing environment
What are the two terms we use to describe animals by how they handle metabolic waste. What is the difference (with two trends)
Endotherms: generate heat as a by-product of metabolism. Typically: elevate body temperate above environment AND are well insulated
Ectotherms: Don’t produce much metabolic heat. Usually regulate body temperature by behavior (have high thermal conductance) AND are not well insulated
What is a term for an animal that is ENDOTHERMIC but not a HOMEOTHERM?
HETEROTHERM
What are the two types of heterotherms? How do they differ?
Temporal: Vary temperature over course of day
Regional: Maintain core temperature and allow periphery to vary
Using our terms, describe:
- Humans
- Birds
- Fish
- Reptiles
- Invertebrates
- Humans and birds: homeotherms, endotherms
- Invertebrates and Fish: Homeotherms, ectotherms
- Reptiles: Endotherms, poikilotherms
What are the four mechanisms of heat transfer?
1) Conduction
2) Convection
3) Evaporation
4) Radiation
Define CONDUCTION
Heat exchange requiring direct contact
Define CONVECTION
Heat exchange by movement of gas or liquid over body
Describe EVAPORATION. Give a metric for this form of heat loss
Heat loss due to conversion of a liquid to a vapor.
Converting 1g water to vapor uses 585 calories
Define RADIATION
Transfer of heat via infrared rays
Describe four ways in which animals adapt membranes in response to colder temperatures
1) Shorter chain length
2) Un-saturation (double bonds)
3) Changing polar head groups (phosphotidylcholine-> phosphotidylethanolamine)
4) More cholesterol (keeps membrane fluid at colder temps)
Name two Antarctic fish:
1) Trematomus borchgrevinki
2) Antarctic toothfish
Name two ways in which fish adapt to colder water:
1) Express different isoforms of LACTATE DEHYDROGENASE (works better at lower temps)
2) Anti-freeze proteins
What do the anti-freeze proteins do? How?
Prevent the nucleation of ice crystals in the body. Binds to ice crystals that are developing, thus stopping growth.
Name one fish that varies LACTATE DEHYDROGENASE
the Barracuda
What are two examples of animals that makes anti-freeze proteins?
1) Antarctic toothfish
2) Siberian Salamander
What’s a cool fact about Siberian Salamanders?
They can survive frozen in ice for years and then thaw out and walk away!
What is a commercial use of antifreeze protein?
Gives low fat ice cream the same texture and taste as high fat ice cream
What are two ways in which animals stay warm?
1) shivering
2) Brown Adipose Tissue (BAT)
How does shivering work?
The body stimulates the skeletal muscles to actively generate heat.
What is the process that brown adipose tissue uses? How does Brown Adipose Tissue work?
NON-SHIVERING THERMOGENESIS: It is highly vascularized and has large numbers of mitochondria. Stimulated sympathetically by norepinephrine, it increases the rate of oxidation of stored lipids, but uncoples this oxidative phosphorylation from the electron transport chain, so all energy is “lost” as heat.
What is the key protein that causes uncopling of the electron transport chain?
THERMOGENIN a.k.a. UCP 1
Do fish have BAT? Do they have non-shivering thermogenesis?
No BAT, no NST
Do birds have BAT? Do they have non-shivering thermogenesis?
No BAT
Yes, thermogenesis occurs in muscles though!
So, BAT developed ______ in evolution
later
When is BAT most prevalent in humans
Fetuses and newborns
Why do newborns need more bat?
Because they can’t shiver
Where is BAT found in humans and animals?
Around the core (chest and all along back)
What is a recent discovery regarding BAT?
Adult humans actually do have BAT, which we didn’t think they did previously
Do lean humans or obese humans have more BAT? What do we find regarding BAT expression?
Lean humans
We find that workers who are subject to cold outdoors express more BAT
What are the three types of adipose tissue in humans? What are their functions?
1) White- energy storage. May convert to BAT
2) Brown- generates heat
3) beige- combination, genesis may be from BAT
Name and state two rules regarding animals in cold environments
1) Bergmann’s Rule: Animals in cold environments tend to be larger
2) Allen’s Rule: Animals in cold climates tend to have shorter extremities
What is one way that seals have adapted to cold water?
Blubber insulation!
What about fur determines how warm it is? How can animals make fur warmer (specific process)
Thickness of fur: thicker= warmer
Neural stimulation causes ERECTOR MUSCLE to make hair stand up, this increases the fur thickness!
What are six animal features that play a thermoregulatory role? What do we call these features? How do they work?
1) Rabbit Ears
2) Toucan beak
3) Human palms (followed by face and feet)
4) Rat tail
5) Dog tongue
6) Bear feet and nose
“HEAT WINDOWS”
Animals can divert bloodflow here to cool down quickly
The toucan’s beak is the _______ of any bird
Largest
Why does cooling improve performance?
MPK (muscle pyruvate kinase) is highly temperature sensitive
Describe another key idea in heat regulation (involves blood vessels distance to skin)
Changing peripheral circulation. We can use a precapillary sphincter to determine if blood goes to the skin (to cool) or takes a shunt to avoid the cold outside
Describe another key idea in thermoregulation (involves blood vessels proximity to one another). Where is it found?
Countercurrent Heat Exchange: Keeping blood vessels close means heat lost by one vessel may be picked up by another.
Found in: legs of reindeer, flippers of seals, penguins and dolphins, bird legs, sheep brain, bluefin tuna red muscle
What is one term for a countercurrent exchanger in the brain? How does it work?
Carotid rete mirabile. Arterial blood meets and is cooled by cool venous blood from nasal passages.
How does panting work?
Animals increase their dead space ventilation (not affecting alveolar ventilation, and thus not affecting partial pressure of co2), and thereby lose heat in the warm, exhaled air. They make sure to alternate shallow panting breaths with deep breaths.
At what rate do animals usually pant? Why?
At the resonant frequency of the chest cavity, to reduce the energy cost
If panting is not done correctly, what could happen?
Hyperventilation could lead to a decrease in CO2, which would lead to a high blood pH, a condition which is called ALKALOSIS.
What is one mechanism employed by birds to reduce heat loss?
Huddling together
What do we call a group of penguins huddled together?
a Creche
What is another animal that huddles?
Naked mole rat
What is one offense use of huddling?
Thermal assassination: Japanese boney bees mob a predatory wasp
List six ways that endotherms respond to cold
1) Vasoconstriction
2) Countercurrent exchange
3) Insulation (fur, blubber)
4) Thermogenesis (BAT)
5) Postural changes (curling up)
6) Behavior (huddling)
List five ways that endotherms respond to heat
1) Vasodilation
2) Heat Windows
3) Insulation Adjustment
4) Evaporative cooling (sweating, panting)
5) Behavior
List one way in which ectotherms respond to cold
1) Prevent intracellular ice crystals by using ANTI-FREEZE PROTEINS
List two ways in which ectotherms respond to heat
1) Control cooling and heating rates of body
2) Behavior (e.g. find shade)
List 6 thermoadaptations of the camel:
1) Ability to tolerate a higher body temperature during the day (avoids water loss associated with heat loss)
2) Countercurrent exchanger brain cooling
3) Countercurrent exchange cooling in the nasal passages
4) Fur insulation to reduce heat and water loss
5) Kidney structure w/ long Loop of Henle favors water reabsorbtion
6) Can tolerate a higher degree of dehydration than others (30% vs 15-20%)
What do we call a drop in body temperature?
Hypothermia
What do we call it when an animal drops body temperature for a period of hours (e.g. overnight)? For a period of months? In response to hot an arid conditions?
- Torpor
- Hibernation
- Estivation
What is one example of an animal that employs torpor? What is this specific type of torpor called? What characterizes torpor (give metrics)? Why?
Anna’s Hummingbird
Noctivation (a.k.a. daily torpor)
Lower metabolism (by 95%), heart rate (1200 beats to 50 beats) and body temperature (3-5 degrees lower)
Because its metabolism is so high that it would starve overnight without feeding
What would we call birds that allow their temperatures to decrease at night to save energy?
Temporal Heterotherms
Discuss four changes in hibernating bears
1) Metabolism drops by 75%
2) Body temp only drops 5-6 degrees (to 91 F)
3) Heart rate drops from 55 b.p.m. to 9 b.p.m.
4) G.I. system atrophies
What do bears do if their body temperature drops too much during hibernation?
SHIVERING THERMOGENESIS
What does temperature distribution in the human body look like at normal temperatures? How about when it gets really hot?
At normal temps, the core and head are 37 C, but the limbs are actually cooler. When its really hot, the limbs heat up as well to try to shed heat.
How many sweat glands do humans have? Where are they mostly located? What causes the release of sweat?
- 3 million sweat glands
- Approx. half on chest and back, also on forehead and palms
- Epinephrine causes release
Discuss the thermoregulatory pathway in humans
Peripheral thermoreceptors on skin and central thermoreceptors in core sense body temperature and report to the hypothalamus and cerebral cortex. The hypothalamus (sympathetic) causes epinephrine release from the adrenal medually, which can excite BAT or sweat glands. The hypothalamus also controls the arterioles and shivering (involuntary skeletal muslce). The cerebral cortex causes movement by skeletal muscles.
What do we call severe overheating? What is the cutoff for core temperature? What is the mortality rate? What is one drug that can cause this if coupled with lots of exercise?
Hyperthermia/ Heat Stroke. 41C. 30%. Ecstasy.
Describe a fever: What is it? What causes it? What is its purpose?
A fever is a NEW SET POINT. Immune system MACROPHAGES release PYROGENS (interleukin-1 and 6), which affects the HYPOTHALAMUS. Elevated temperate designed to kill invaders.
