Thermogenesis and thermoregulation

Question 1

Why is it important to maintain body temp?

Answer 1

• most have a narrow range they have to maintain it in
• > 40 degrees enzymes denature
• organisms have an optimum range

Question 2

What is an ectotherm?

Answer 2

Body temperature is principally dependent on external heat sources

Question 3

What is an endotherm?

Answer 3

Body temp is principally dependent on internally generated metabolic heat

Question 4

What is the thermal neutral zone?

Answer 4

Range of environmental temperature over which the body temperature doesn’t really change

Question 5

Define metabolism

Answer 5

The totality of an organisms chemical reactions, consisting of catabolic and anabolic pathways, which manage the material and energy resources of the organism

Question 6

Define metabolic rate

Answer 6

Measure of the total energy metabolised by an animal in a unit time

Question 7

Define thermoconformer

Answer 7

• Body temperature fluctuates with environmental temp

Question 8

Define Thermoregulator

Answer 8

Maintain body temp over a limited range regardless of changes in environmental temp

Question 9

What happens to metabolism outside the thermal neutral zone?

Answer 9

Increases to retain a comfortable body temp

Question 10

What mechanisms are involved in thermoregulation in endotherms?

Answer 10

• insulation (Retain heat)
• Vasoconstriction and Vasodilation (adjust rate of heat exchange)
• Counter current heat exchange (prevents cold blood going to the core, cold extremities, blood flows in parallel)
• Panting
• sweating
• bathing
• migrating
• shivering/non shivering thermogenesis

Question 11

Which mechanisms are involved above the thermal neutral zone

Answer 11

• Panting and sweating (heat loss by evaporation)

- Vasodilation (heat loss through blood vessels)

Question 12

Which mechanisms are involved below the thermal neutral zone

Answer 12

• increase metabolism
• Shivering thermogenesis - Contractions of antagonistic skeletal muscle, ATP is used to fuel the movements, Energy released as heat
• Non shivering thermogenesis - Brown adipose tissue is packed with fat cells, packed with mitochondria, when temp drops, the neurotransmitter noreopinephrine sends a signal which switches the function of the mitochondrial membrane from ATP production to heat generation, Use a proton which passes through the membrane through uncoupling proteins and releases heat instead of making ATP.

Question 13

Why doesn’t metabolism in ectotherms have much of an effect on body temp?

Answer 13

• have lower metabolic densities

- amount of heat generated is small

Question 14

What are regional endotherms?

Answer 14

The ability of some ectothermic fish to maintain certain body areas at high temperatures than the surrounding water, by means of vascular counter current heat exchange/specialized thermogenic organs

Question 15

Give 2 examples of regional endotherms

Answer 15

• Stevens et al, 1974 - in most tuna blood is delivered to red muscle via subcutaneous arteries and returned to vessels, creating a counter current heat exchange and a strong temperature gradient across the body, helping heat the core.
• Fritsches et al 2005 - sword fish can warm their brain, have highly specialised heating system behind eyes, warms eyes and brain above ambient temp, heat generated as a by-product of the transfer of calcium, allows them to see better

Question 16

Give 4 examples of thermoregulation in ectotherms

Answer 16

1. Tanaka et al, 2012 - Depth selection in pacific salmon, swim up and down to balance body temp (behavioural)
2. Chapperon & seuront 2011 - littorina sp. select a substrate temp that’s below their thermal max (micro habitat selection)
3. Helmuth 1998 - Clumping in mussels, advantage when hot as solitary mussels 2.5 degrees warmer
4. Smith & Miller 1973 - Uca spp use burrows to keep them cool