Module 11 - Thermoregulation Flashcards
(38 cards)
What are ectotherms?
Animals that use external environment to regulate body temperature by gaining/losing heat via convection, conduction & radiation
What are the 2 broad categories of response?
poikilothermy
ectothermic regulation
Describe poikilothermy…?
Ectotherms that live in environments where temp VARIES -> body temp VARIES
Metabolic rates typically low in cold, high in hot
What behavioural adaptations do poikilotherms use?
avoid extreme temps
if extreme temps cannot be avoided - limit physiological heat-loss mechanisms like evaporation (internal biochemistry) or enter dormancy
Which poikilotherms would typically have a more/less variable body temperature?
terrestrial (more variable), aquatic (less variable)
Describe ectothermic regulation…?
animals that CANNOT COPE with any significant temp changes
Many use EXTERNAL HEAT EXCHANGES to keep temps at or near optimum
In a constant environment (eg cold deep sea), the ectotherm is essentially a …?
homeotherm (maintains a stable internal body temperature)
Describe the process of external heat exchange and give example of animal using this process
- Gain external heat/avoid loss to cold environ’s (cold morning -> lizard basks in sunlight)
- Retain internal heat (lizard vasoconstricts blood vessels at skin -> reduce heat loss)
- 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)
- 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)
As ectotherms, how do butterflies regulate body temperature?
seasonally migrate
Ectothermic regulators in thermally variable environments are also … part of the time?
poikilotherms - metabolically compensate for changes in body temp.
Explain how poikilotherms adapt to changes in temperature, and what happens to poikilotherms in extreme environments?
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
Explain how acclimatisation to environmental extremes can be achieved to maintain useful level of activity?
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)
Describe 2 other forms of metabolic compensation & give an example of animal that uses one of them…?
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
How can turtles adapt to extreme cold environments?
- Lower metabolic rates - decrease rate of ATP consumption
- hibernate at depths below frost line - survive whole winter without breathing & with 1bpm HR
Adaptations of animals whose body temperature falls below freezing…?
- Freeze tolerance
- freeze avoidance
Describe freeze tolerance and give example of animal that uses this adaptation…?
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
Describe freeze avoidance, how it works & give some examples of animals that use this adaptation…?
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
What is the heat shock response?
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
Describe in detail the pathway involved in the heat shock response from a normal state -> sudden heat stress…?
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
Define endoderms…?
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
What is one of the main issues with endotherm metabolisms?
high metabolisms -> increased risk of overheating thus need mechanisms to remove excess heat
What mechanisms & behaviours do endotherms employ in order to maintain internal core temperatures in cold environments?
- 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
Describe the process of retaining internal heat in endotherms?
- 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)
Describe in detail countercurrent exchangers…?
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
