Lecture 25 And 26: Thermoregulation

Question 1

Give definition of heat and temperature

Answer 1

Heat= total kinetic energy of all molecules in system
Temperature= mean kinetic energy of molecules in a system
-detainees direction of heat flow

Question 2

Total heat is the sum of all

Answer 2

Total heat= metabolic h + conduction h + convection h + radiation h + evaporation h + stored h

Question 3

Conduction:

Answer 3

Movement of heat from high to low temperatures by interaction of adjacent molecules
Influenced by: 
-thermal conductivity (k) 
-area (a) through which heat flows
-temperature gradient 
-separation distance

Question 4

Convection:

Answer 4

Movement of heat through a fluid (liquid or gas) by mass transport of currents
Influences by:
-temperature gradient
-convection coefficient -dependant on body shape (surface area), wind speeds (or water current) - free convection vs forced convection

Question 5

Radiation

Answer 5

Energy transfer by means of electromagnetic energy-travels at speed of light and needs no medium of propagation
Influenced by:
-absolute temp
-surface area

Question 6

Evaporation

Answer 6

Evaporation of water requires loss of heat 
Influenced by: 
-temp gradients 
-vapour pressure gradients 
-surface area
-wind speeds

Question 7

How is heat exchanged in the body?

Answer 7

Because tissues are poor conductors, heat is most effectively transferred in the blood
-countercurrent mechanisms are used to both conserve and lose heat

Question 8

Heat transfer

Effect of size and shape on heat loss

Answer 8

Body size affects heat exchange: (thermal inertia)
-elephant: high thermal inertia
Mouse: low thermal inertia
-elongated shapes increases heat loss/gain

Question 9

Heat transfer:

Bergmanns rule

Answer 9

“Animals from cooler climates tend to be of larger body size and hence have smaller SA to Vol ratios than animals of the same species living in Warner climates.

Question 10

Heat transfer:

Alleys rule

Answer 10

“Animals adopted to cold have smaller and shorter limbs and protruding body parts”
From the northern arctic hare to to southern desert jackrabbit
Refer to slide 16 for image

Question 11

Thermal strategies:
Based on the stability of Tb (body temp)
Poikilotherm
Homeotherm

Based on the source of thermal energy
Ectotherm
Endotherm

Answer 11

Based on the stability of Tb (body temp)
Poikilotherm: body temp changes with ambient temp
Homeotherm: regulates body temp by physiological means (not just behaviour)

Based on the source of thermal energy
Ectotherm: thermal balance depends on external source of heat
Endotherm: thermoregulation depends on metabolic heat production
Most animals are best described by a combination of terms
Refer to slide 21 for picture

Question 12

Explain
Temporal heterotherms:
Regional heterotherms:

Answer 12

Temporal heterotherms undergo prolonged changed in body heat

• hibernating animals
• pythons after large meal

regional heterotherms retain heat in specific regions of the body

• billfish with heater organs in near their eyes
• tu a retain heat within red muscles

Question 13

Thermal strategies

Humans

Answer 13

Maintains a near constant core temperature, but the extremities (hands, feet, testicle) may be colder.
Core Tb may vary during the reproductive period for females and increases as a result of a fever

Question 14

For a human what is the temp that indicates you have a fever?

Answer 14

> 38 degrees Celsius

Question 15

The vertebrate thermostat- Amphetamines

Answer 15

Amphetamines (eg ecstasy, speed, ice) are associated with significant morbidity and mortality, largely due to the disturbances caused in thermoregulation.

• effects range from mild tremor, headache, excessive sweating, blurred vision and muscle cramps
• to severe and hypothermia, seizures, multi-organ failure and death

Question 16

What are the three things we can change for thermoregulation

Answer 16

1. Heat production
2. Insulation
3. Body temp

Question 17

Cold: heat production. What are some coping strategies?

Answer 17

1. Shivering: using locomotion to generate heat
2. Non shivering thermogenesis:
   - enzyme systems for fat metabolism activated to produce energy (heat) occurs in both regular fat and ‘brown fat’
3. Increased basal metabolic rate
4. Insulation: different for arctic and tropical animals

Question 18

Cold: increase insulation

Explain

Answer 18

A layer of material that reduces thermal exchange
Types:
Internal insulation: blubber
External insulation: hair, feathers, air, water
Effectiveness of insulation depends on thickness

Piloerection:

• hair and feathers act as insulation
• efficiency of insulation depends on its thickness
• animals get fluffier when it is cold
• hair on feathers are pulled perpendicular by smooth muscle (erector muscles) attach at their bases

Question 19

Comparison of blubber and fur for insulation

Answer 19

Insulation of fur cannot be bypassed

Question 20

Cold: behaviour

Hibernation

Answer 20

Huddling eg emperor penguins

Hibernation: seasonal

Question 21

Body temperature and metabolism
Poikilotherm VO2
Homeotherm

Answer 21

Poikilotherm: VO2 increases with increase in Ambient temp
Homeotherm: VO2 decreases with ambient temp, then is independant after critical point

Question 22

Homeotherms: 
Thermal zones
Thermoneutral zone
Upper critical temperature 
Lower critical temperature
Eurythermic
Stenothermic

Answer 22

Thermoneutral zone: range of temperatures that are optimal for physiological processes; metabolic rate is minimal (basal metabolic rate)
Upper critical temperature: metabolic rate increases to induce a physiological response to recent overheating
Lower critical temperature: metabolic rate increases to increase heat production
Eurythermic: have a wide thermoneutral zone
Stenothermic: have a narrow thermoneutral zone

Question 23

Poikilotherms vs homeotherms

1. Source of heat
2. Anaerobic vs aerobic activity

Answer 23

Amphibians and reptiles are ectotherms = low energy approach to life. Low metabolic rate (VO2)

Birds and mammals are endotherms = high metabolic rate (VO2) and is independant of Ta

Question 24

Where is the internal thermostat located on mammals? Send birds?

Answer 24

Mammals:
-information from the central and peripheral thermal sensors are integrated in the hypothalamus
Birds:
-the thermostat is located in the spinal cord

Sends signals to the body to alter the rates of heat production and dissipation.
Negative feedback information ie a homeostatic process

Question 25

All animals have a critical thermal maximum, above which long-term exposure can be fatal

Answer 25

Eg protein denaturation, and decreased affinity for Hb for O2

Question 26

Hot: effect of size

Answer 26

1. Height of the ground
2. Ability to move to a more suitable habitat
3. More efficient locomotion
4. Thermal inertia (also thick of their body shape)
   Larger animals have advantage of size in the dessert
   Small mammals in hot environment rely most on behavioural thermoregulation eg retreat to burrows, eg become nocturnal.

Question 27

Hot:

a) increased conductance (inverse of insulation)
b) evaporative cooling

Answer 27

A) a rise in 0.5 degrees causes peripheral vasodilation eg flushed skin after activity
-in the rabbit, heat loss is through ears (more blood flow there)
B) evaporative cooling
-1g of water removes 2,4 kJ of heat

Question 28

Hot: temporal heterothermy

Answer 28

Diurnal heterothermy
Eg antelope and camel
Have massive changes in body temp thought the day depending on the temp

Question 29

Hot: selective brain cooling

Answer 29

Carotid rete- countercurrent heat exchange
Eg the brain of a gazelle can be kept at Lowe temp than body core coz arterial blood, before it reaches the brain, passes in small arteries through a pool of cooler venous blood that drains from the nasal region, where evaporation takes place .
Selective brain cooling can save evaporative water loss