Module 11 - Thermoregulation Flashcards Preview

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Flashcards in Module 11 - Thermoregulation Deck (38)
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1
Q

What are ectotherms?

A

Animals that use external environment to regulate body temperature by gaining/losing heat via convection, conduction & radiation

2
Q

What are the 2 broad categories of response?

A

poikilothermy

ectothermic regulation

3
Q

Describe poikilothermy…?

A

Ectotherms that live in environments where temp VARIES -> body temp VARIES
Metabolic rates typically low in cold, high in hot

4
Q

What behavioural adaptations do poikilotherms use?

A

avoid extreme temps
if extreme temps cannot be avoided - limit physiological heat-loss mechanisms like evaporation (internal biochemistry) or enter dormancy

5
Q

Which poikilotherms would typically have a more/less variable body temperature?

A

terrestrial (more variable), aquatic (less variable)

6
Q

Describe ectothermic regulation…?

A

animals that CANNOT COPE with any significant temp changes

Many use EXTERNAL HEAT EXCHANGES to keep temps at or near optimum

7
Q

In a constant environment (eg cold deep sea), the ectotherm is essentially a …?

A

homeotherm (maintains a stable internal body temperature)

8
Q

Describe the process of external heat exchange and give example of animal using this process

A
  1. Gain external heat/avoid loss to cold environ’s (cold morning -> lizard basks in sunlight)
  2. Retain internal heat (lizard vasoconstricts blood vessels at skin -> reduce heat loss)
  3. Generate more internal heat (does not occur significantly in pure ectotherms; some large lizards (Komodo dragon) warm up temporarily from high locomotory activity retaining heat cos of low SA:BW ratio)
  4. Lose excess internal heat/avoid gains from hot environment (blood vessels in lizards skin dilate -> increase heat loss; evaporation from mouth -> cooling; if too hot -> seeks shade)
9
Q

As ectotherms, how do butterflies regulate body temperature?

A

seasonally migrate

10
Q

Ectothermic regulators in thermally variable environments are also … part of the time?

A

poikilotherms - metabolically compensate for changes in body temp.

11
Q

Explain how poikilotherms adapt to changes in temperature, and what happens to poikilotherms in extreme environments?

A

UNDERGO ADAPTIVE PHYSIOLOGICAL CHANGES
Too cold -> metabolism slow down to point where obtaining food not possible (freezing may kill it)
Too hot -> membranes, proteins & nucleic acids irreversibly damaged

12
Q

Explain how acclimatisation to environmental extremes can be achieved to maintain useful level of activity?

A

Achieved thru METABOLIC COMPENSATION

  • Homeoviscous membrane adaptation (restructuring membranes to maintain proper fluidity)
  • pH regulation (most ecto’s have higher internal pH than warmer animals)
13
Q

Describe 2 other forms of metabolic compensation & give an example of animal that uses one of them…?

A

ISOFORM REGULATION - different forms of same protein used at different temps
common carp -> expresss different forms of myosin & myosin light-chain (MLC) protein in summer & winter -> IN THE COLD, these isoforms -> greater speed & force, but muscle does not work well at higher temps
ENZYME CONCENTRATION CHANGES - increased level of metabolic enzymes esp. in aerobic pathways
frogs & fish -> convert energy from food more efficiently, however limiting strategy as takes energy to produce energy

14
Q

How can turtles adapt to extreme cold environments?

A
  • Lower metabolic rates - decrease rate of ATP consumption

- hibernate at depths below frost line - survive whole winter without breathing & with 1bpm HR

15
Q

Adaptations of animals whose body temperature falls below freezing…?

A
  • Freeze tolerance

- freeze avoidance

16
Q

Describe freeze tolerance and give example of animal that uses this adaptation…?

A

up to 80% of body water can be frozen
65% in Spring peeper frogs -> ATP virtually ceases & minimal neurological activity detected
Metabolic steps involved:
freezing temps -> frozen water on skin -> signals liver -> large glycogen breakdown -> increase [BG] 450-fold -> serves as anti-freeze by lowering freezing point.
In < 8hrs frogs organs loaded with glucose acting as COMPATIBLE CRYOPROTECTANT -> OSMOTIC BALANCE
During thawing -> glucose immediately available for ATP generation

17
Q

Describe freeze avoidance, how it works & give some examples of animals that use this adaptation…?

A

over-wintering animals considered intolerant to freezing but may still have body temps. below freezing
contain antifreeze compounds, used differently
Some use COMPATIBLE CRYOPROTECTANTS (sorbitol & glycogen) throughout ECF & ICF -> ECF protected from freezing (insects & arachnids)
Other insects & polar fishes use ANTIFREEZE PROTEINS -> effective at much lower [ ] than compatible cryoprotectants -> prevent growth of ice crystals
SUPERCOOLING -> some over-wintering animals (fishes & arachnids) -> temp well below freezing but no trigger to trigger to begin ice formation, but is dangerous as contact with ice can trigger rapid crystallisation of body fluids

18
Q

What is the heat shock response?

A

any organism exposed to sudden temp increase of 5 degrees or more -> HEAT SHOCK RESPONSE -> gene activation of HSP(protein)s -> protect cells from heat death

19
Q

Describe in detail the pathway involved in the heat shock response from a normal state -> sudden heat stress…?

A

in unstressed/normal cell, small amounts of inactive HSP 70 bound to HSF-1
add heat stress…
HSP 70 detach from HSF(factor)-1 -> binds to unfolded proteins, also activates 3, HSF-1 transcription factors -> form trimer -> nucleus -> HSE(element) -> transcription of HSP genes

20
Q

Define endoderms…?

A

Must constantly generate heat internally to maintain body temp -> usually oxidation of metabolic fuel derived from food
IMPORTANT POINT -> CONSUME 5-20 TIMES MORE ENERGY THAN ECTOTHERMS OF SAME MASS

21
Q

What is one of the main issues with endotherm metabolisms?

A

high metabolisms -> increased risk of overheating thus need mechanisms to remove excess heat

22
Q

What mechanisms & behaviours do endotherms employ in order to maintain internal core temperatures in cold environments?

A
  • Similar BEHAVIOURS to endotherms - eg seeking out sunshine/warm surfaces avoiding excess environmental cold
  • ANATOMICAL FEATURES - dark skin -> absorbs solar radiation
  • RETAIN INTERNAL HEAT
  • GENERATE MORE INTERNAL HEAT
23
Q

Describe the process of retaining internal heat in endotherms?

A
  • vasoconstriction
  • anatomical insulation (feathers, adipose, hair)
  • behavioural insulation (nest-building, burrowing, huddling)
  • larger body size in cold climates
  • countercurrent exchangers (blood flow to retain core heat)
24
Q

Describe in detail countercurrent exchangers…?

A

veins & arteries in dense array called RETE MIRABILE - vessels so closely packed together -> nearly in thermal equilibrium
blood flow in opposite direction (concurrent)
PROCESS -> warm core blood moves out arteries towards cold peripheral tissue; in RETE, encounters cold blood from periphery
By conduction, heat moves into cold vein -> thus back to core

25
Q

Describe the process of generating more internal heat…?

A
  • KEY adaptation is large increase in overall BMR (birds & mammals)
  • increased skeletal muscle activity (shivering) & to lesser extent, hormonal actions -> CHEMICAL THERMOGENESIS
26
Q

Describe the process of chemical thermogenesis in endotherms…?

A
  • mediated by adrenaline & thyroid hormone
  • cellular mechanisms -> heat not fully understood
  • newborn mammals & small mammals have brown fat deposits -> efficiently converts chemical energy -> heat
    Also, brown fat dissipates chemical energy (heat) via mitochondrial uncoupling protein 1
27
Q

How does an endotherm re-balance an increased core temperature?

A

LOSING EXCESS HEAT/AVOIDING GAINS FROM HOT ENVIRONMENTS

  • decrease insulation (desert endotherms, camels virtually no sub-cut. fat -> hump, hair shedding)
  • vasodilation of arterioles -> increase flow heated blood thru skin -> heat loss
  • enhanced evaporation (panting, sweating)
  • countercurrent exchange (eg. gazelles have rete between brain & core body -> warm blood carotid artery -> cool venous blood from nose & facial skin -> protects brain from high heat prod. by skeletal muscle when running (also Orca example…)
  • avoidance behaviour - seeking shade, wallowing in water, moving to higher altitudes
  • anatomical decrease of heat gain (light coloured skin)
28
Q

How do Orcas circulatory systems regulate body temp?

A

slide 14 - endotherms lec

29
Q

Countercurrent exchange in horses involves what?

A

cooling sinuses

guttural pouches

30
Q

How and where does integration of thermosensory inputs occur?

A

Thermosensory inputs from core & body -> hypothalamus

In vertebrates, hypo. controls thermoreg. via -ve feedback

31
Q

Heterotherms…?

A

Animals that exhibit characteristics of both poikilothermy & homeothermy

  • do not heat all their cores
  • small birds & mammals cannot maintain high core temps. continuously due to: high SA:BW or insufficient food supplies
32
Q

What are regional heterotherms? Give an example of one & how it utilises this anatomical strategy to thermoregulate.

A

Animals that only heat certain organs
eg bees & moths heat thoraxes by activity of flight muscles in 2 ways
- shivering flight muscles before take-off
- during flight -> thorax relatively constant & high temp via haemolymph flow btw thorax & abdo. (concurrent flow channels)
To dissipate heat -> venous blood pumped without arterial flow -> heat to thermal window -> removal

33
Q

Describe how regional heterotherms, tuna & sharks regulate thermoregulation.

A

Countercurrent rete system between aerobic (red) muscle & gills prevent most heat loss -> presumably allows them to move btw warm & cold waters more easily than ectotherms
(rete traps heat generated by deep red muscles)

34
Q

What are temporal heterotherms?

A

Animals that maintain high body temps only for certain periods
Eg. hibernation & daily torpor

35
Q

Describe the process of hibernation & give an example of an animal that uses this adaptive strategy.

A

Many SMALL ENDOTHERMS at higher latitudes -> poikilothermic at winter -> dormant state -> body temp. ~0 degrees celcius (eg. Arctic ground squirrel)
Can do this by storing large amounts of un-sat. fats (sat. fats harden in cold)
mammalian hibernators - have functioning hypo. thermostat but greatly lowered set point
- prevent body freezing by generating heat using uncoupling proteins in brown & white adipose & skeletal muscle
- go thru ‘bouts’ of rewarming & re-cooling every few days/weeks

36
Q

Which animals ‘truly hibernate’?

A

ONLY SMALL MAMMALS (<3kg)
bears are too large to cool off & reheat in springtime - sleep thru much of winter with body temp. only few degrees lower than normal

37
Q

What is torpor? Give example of animal that utilises this adaptive strategy.

A

many small endotherms enter daily hibernation-like state (torpor)
Deer mouse - night -> body temp. decreases from ~35 degrees -> 15-20 degrees -> saves lots of energy. Does not drop too low (freezing) as too much energy expended rewarming on daily basis
Needs constant food input to maintain metabolism in active state

38
Q

A big advantage of torpor?

A

longer life spans
decrease of metabolism on daily basis -> slows ageing (via reactive oxygen species (ROS) generated in proportion to metabolic rate)