Module 11 - Thermoregulation

Question 1

What are ectotherms?

Answer 1

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

Question 2

What are the 2 broad categories of response?

Answer 2

poikilothermy

ectothermic regulation

Question 3

Describe poikilothermy…?

Answer 3

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

Question 4

What behavioural adaptations do poikilotherms use?

Answer 4

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

Question 5

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

Answer 5

terrestrial (more variable), aquatic (less variable)

Question 6

Describe ectothermic regulation…?

Answer 6

animals that CANNOT COPE with any significant temp changes

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

Question 7

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

Answer 7

homeotherm (maintains a stable internal body temperature)

Question 8

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

Answer 8

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)

Question 9

As ectotherms, how do butterflies regulate body temperature?

Answer 9

seasonally migrate

Question 10

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

Answer 10

poikilotherms - metabolically compensate for changes in body temp.

Question 11

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

Answer 11

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

Question 12

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

Answer 12

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)

Question 13

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

Answer 13

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

Question 14

How can turtles adapt to extreme cold environments?

Answer 14

• Lower metabolic rates - decrease rate of ATP consumption

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

Question 15

Adaptations of animals whose body temperature falls below freezing…?

Answer 15

• Freeze tolerance

- freeze avoidance

Question 16

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

Answer 16

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

Question 17

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

Answer 17

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

Question 18

What is the heat shock response?

Answer 18

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

Question 19

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

Answer 19

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

Question 20

Define endoderms…?

Answer 20

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

Question 21

What is one of the main issues with endotherm metabolisms?

Answer 21

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

Question 22

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

Answer 22

• 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

Question 23

Describe the process of retaining internal heat in endotherms?

Answer 23

• 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)

Question 24

Describe in detail countercurrent exchangers…?

Answer 24

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

Question 25

Describe the process of generating more internal heat…?

Answer 25

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

Question 26

Describe the process of chemical thermogenesis in endotherms…?

Answer 26

• 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

Question 27

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

Answer 27

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)

Question 28

How do Orcas circulatory systems regulate body temp?

Answer 28

slide 14 - endotherms lec

Question 29

Countercurrent exchange in horses involves what?

Answer 29

cooling sinuses

guttural pouches

Question 30

How and where does integration of thermosensory inputs occur?

Answer 30

Thermosensory inputs from core & body -> hypothalamus

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

Question 31

Heterotherms…?

Answer 31

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

Question 32

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

Answer 32

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

Question 33

Describe how regional heterotherms, tuna & sharks regulate thermoregulation.

Answer 33

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)

Question 34

What are temporal heterotherms?

Answer 34

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

Question 35

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

Answer 35

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

Question 36

Which animals ‘truly hibernate’?

Answer 36

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

Question 37

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

Answer 37

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

Question 38

A big advantage of torpor?

Answer 38

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