Thermoregulation and Energetics

1
Thermoregulation and Energetics
why is temperature important?
2

• Ectothermy and Endothermy
• Ectotherms animals which obtain most of their
  heat from sources outside the body
• Poikilotherms animals whose body temperature
  varies with the environment
• Ectotherms attempt to regulate their temperatures
  within broad limits by behavioural means.

3

• Endotherms animals which maintain their body
  temperatures irrespective of the environmental
  temperature.
• Homoiotherms animals whose body temperature
  remains the same, e.g. birds mammals

Endothermic birds mammals are successful lives
in polar regions
4

• The higher the body temperature the higher the
  metabolic rate of the animal.
• Birds have a higher body temperature than mammals
  (40-44oC) because of the energy demands of flight
  and more heat loss due to a greater temperature
  gradient with the surrounding.
• Advantage much more environmental independence

5

• The body temperature of the Naked Mole Rat, a
  mammal, varies with that of its burrow. It is
  ectothermic, homeothermic (the temperature of the
  burrow, and therefore the animal, does not vary
  widely),

6

• The body temperature of a hibernating bear, a
  mammal, reflects the outside temperature, which
  remains fairly constant, and its metabolism is in
  a very low state. Therefore, when hibernating, it
  is ectothermic, homeothermic

7

• The body temperature of the Hawk Moth, an insect,
  reflects the temperature of its surroundings when
  at rest. However, its huge wing muscles can raise
  its body temperature much higher than that of its
  surroundings. It is endothermic, poikilothermic

8
(No Transcript)
9
Examples of Endotherms and Ectotherms

• Endotherms
• mammals, birds
• Ectotherms
• fish, amphibians, reptiles, invertebrates

10
Endotherms have high and constant body
temperatures because they

• Have relatively high metabolic rates
• 10 X that of similarly sized ectotherms
• Have ways to reduce heat loss
• insulation
• hair
• feathers
• blubber
• circulatory heat exchangers
• specialized capillary beds where cold venous
  blood passes by hot arterial blood (retes)

11
(No Transcript)
12
Endothermy has costs and benefits

• High rates of metabolism must be supported by
  high feeding rates
• only possible if insulation slows heat loss
• only possible above minimum body sizes

13
Endothermy has benefits

• High and constant body temperature allows high
  metabolic and physiological rates
• High degree of ecological independence
• nocturnal
• cold environments (north temperate, arctic)

14

• Endotherms produce metabolic heat to elevate body
  temperature
• ectotherms depend mostly on environmental sources
  of heat.

15

• Ectotherms and endotherms can regulate body
  temperature through behavior.

16
(No Transcript)
17
The hypothalamus acts as a thermostat to control
heat production
18
Position of hypothalamus
19
The hypothalamus acts as a thermostat to control
heat loss
20
(No Transcript)
21
Sympathetic nerve
22
(No Transcript)
23

• 25.2.3 Maintain A Constant Body Temperature in
  Warm Environments
• These adaptations may be physiological or
  behavioural or long term response
• 1. Vasodilation

24

• 25.2.3 Maintain A Constant Body Temperature in
  Warm Environments
• These adaptations may be anatomical,
  physiological or behavioural
• 1. Vasodilation

2. Sweating 3. Panting and licking 4.
Insulation 5. Large surface area to volume ratio
Arctic fox (top) and fennec fox (bottom) showing
differences in lengths of ears
25

• 25.2.3 Maintain A Constant Body Temperature in
  Warm Environments
• These adaptations may be anatomical,
  physiological or behavioural
• 1. Vasodilation
• 2. Sweating
• 3. Panting and licking
• 4. Insulation
• 5. Large surface area to volume ratio

6. Variation in body temperature, e.g. camels
(34-41oC) - reduce temp gradient -
reduce sweating 7. Behavioural mechanisms, e.g.
summer hibernation (aestivation), nocturnal
26
25.2.4 Maintain A Constant Body Temperature in
Cold Environments

• They include
• 1. Vasoconstriction

27
They include1. Vasoconstriction

• 2. Shivering
• 3. Insulation, e.g. fat, fur or feathers

28
They include1. Vasoconstriction

• 2. Shivering
• 3. Insulation, e.g. fat, fur or feathers

4. Small surface area to volume
ratio 5.Variations between superficial and core
temperature with counter-current heat exchange
system to reduce heat lost by extremities (limbs)
of animals
29
(No Transcript)
30
They include1. Vasoconstriction

• 2. Shivering
• 3. Insulation, e.g. fat, fur or feathers

4. Small surface area to volume
ratio 5.Variations between superficial and core
temperature with counter-current heat exchange
system to reduce heat lost by extremities (limbs)
of animals

• 6. Increased metabolic rate
• 7.Behavioural mechanisms, e.g. diurnal, grouping
  together, reproductive behaviour
• 8.Hibernation, eg. squirrel spending brown
  adipose tissue

31

• 25.2.5 Role of The Hypothalamus in the Control of
  Body Temperature
• There are two centres heat gain and a heat loss
  centres.
• It monitors the temperature of blood passing
  through it with nerves coming from receptors in
  the skin about external temperature changes.
• Any reduction in blood temperature will bring
  about changes which conserve heat.
• A rise in blood temperature has the opposite
  effect.

32
(No Transcript)
33
Mechanism for temp regulation

• Behaviour change
• Physical mechanism to regulate body temp
• hair, feathers
• subcutaneous fat

34
Mechanism for temp regulation

• Physical mechanism to regulate body temp
• Change in peripheral blood flow
• 1. Adjusts relative thickness of insulating shell
  

35

• Physical mechanism to regulate body temp
• reduced peripheral blood flow
• 2. Countercurrent heat exchange

36

• Physical mechanism to regulate body temp
• Change in peripheral blood flow
• 3. Cutaneous blood vessels

37



38
Response to Cold Environment

• Strategy is to minimize heat loss and maximize
  heat production
• B. Increase in sympathetic activity
• 1. Increases thickness of insulating shell
• 2. Stimulates nonshivering thermogenesis
• 3. Initiates piloerection
• C. Shivering thermogenesis
• Synchronous, rhythmic contractions of
  antagonistic muscles
• D. Long-term cold exposure
• 1. Stimulates hypothalamus to produce more TRH

39
(No Transcript)
40
Staying Warm
Counter current exchange in legs and feet results
in very low heat loss due to conduction between
foot and ground entering arterial blood flow in
close proximity to exiting venous blood legs get
oxygen without giving up heat
Emperor penguins
41
1999 II (4)A healthy young man lost his way
while hiking alone in a mountain area. He spent a
night in the open without any food but he had a
bottle of water with him. During the night, he
felt cold and hungry, and he was anxious and
frightened. Give a full account of how his
nervous and endocrine systems reacted to this
situation.(20 marks)
42
1999 II (4)A healthy young man lost his way
while hiking alone in a mountain area. He spent a
night in the open without any food but he had a
bottle of water with him. During the night, he
felt cold and hungry, and he was anxious and
frightened. Give a full account of how his
nervous and endocrine systems reacted to this
situation.(20 marks)
43
(No Transcript)
44
Metabolic responses to decreasing temperatures
are shifted due to insulation differences
45
(No Transcript)
46
(No Transcript)
47
Metabolic Rate
Environmental Temperature
48
Increasing heat production

• By regulating metabolic rate

49
Endotherms, large and small have three main
problems

• Getting warm
• especially hard if
• you are small
• smallest endotherms use torpor (heterothermy) to
  survive
• rousing from torpor is expensive (brown fat)
• the environment is cold
• smallest endotherms are not found in the coldest
  climates
• Staying warm
• insulation
• countercurrent heat exchangers
• Overheating
• circumventing water saving nasal passages to
  maximize evaporative cooling

50
Getting Warm Brown Fat

• Brown fat located in thorax next to the heart
• specialized fat cells metabolize their own lipids
  producing enormous quantitites of heat
• high vascularity of the fat body leads to rapid
  warming of the blood and transfer to other parts
  of the body

Torpor in bats energy savings and cost of arousal
51
Cooling Off
Arterial blood flows over the tongue and through
the nasal turbinates cooled by evaporation water
lost, but the venous blood is cooled arterial and
venous blood flow past eachother in a rete before
arterial blood flows to the brain