Thermoregulation

Question 1

What are all the physiological mechanisms that help an animal regulate its temperature?

Answer 1

Brain/hypothalamus

Skin

Viscera

Spinal Cord

Around major veins

Question 2

How does the hypothalamus and mid-brain work to help regulate body temperature? When it’s too hot & too cold?

Answer 2

Like thermostat that can be reset
- changes “set point” higher during exercise so animal can withstand higher body temperature

Too hot:

Causes vasodilation, sweating & panting to promote heat loss

Too cold:

Vasoconstriction

Shivering

Non-shivering thermogenesis to promote heat gain

Question 3

What elements of and in the skin enable it to help regulate body temperature?

Answer 3

Sweat glands

Arterioles

Temperature sensors (thermoreceptors)

Piloerection of Hair/Fur/Feathers

Question 4

How do thermoreceptors and arterioles work together in the skin to regulate body temperature?

Answer 4

If it’s too hot

Arterioles dilate
↓
Increased capillary blood flow

↓
Increase temperature gradient

↓
Decrease tissue insulation
↓
Much heat radiated

If it’s too cold:

Arterioles constrict
↓
Reduced capillary blood flow

↓
Decrease temperature gradient

↓
Increase tissue insulation
↓
Little heat radiated

Question 5

How do sweat glands help the skin regulate body temperature?

Answer 5

Sweat glands aid in evaporative heat loss (sweating);
- water & ions diffuse into sweat gland from capillary, with different osmotic compositions depending on temperature-regulating requirement

If it’s hot:

More ions (and therefore water) transfer into sweat gland from blood plasma, leaves by evaporation (sweating) & thus body can become dehydrated.

If it’s cold:

Fewer ions (and therefore water ) enter sweat gland from blood plasma, so body stays hydrated (doesn’t sweat)

Question 6

How does pilorection of the hairs or feathers help the skin regulate body temperature?

Answer 6

If it’s hot:

Hair/feathers lie flat to decrease boundary layer (insulation) to promote heat loss.

**If it’s cold: **

Hair/feathers stand up to increase boundary layer (insulation) to limit heat loss.

Question 7

How does viscera help the body regulate body temperature?

Answer 7

The internal organs can sense the temperature of food & drink ingested and thus can help reset the body temperature.

Question 8

How does the spinal cord help to regulate body temperature?

Answer 8

Sensation from the periphery sent to CNS along spinal cord, then motor innervation to help regulate body temp.

If hot:

Increased panting & sweating

Decreases vasomotor tone

If cold:

Increases vasomotor tone (muscles constrict)

Increases thermogenesis (shivering)

Question 9

Explain how the area around major veins can help regulate body temperature.

Answer 9

Blood vessels running in opposite directions set up counter-current system, so heat is transferred from warm blood to cool blood in deeply embedded veins that will will dilate.
When need cooling down, warm blood in superficial areas will dilate to cool down.

If it’s hot:

Superficial veins dilate, causing change in pressure gradient: Heat transferred from warm blood in deep arteries and capillaries to cool blood in veins; heat lost near surface of extremities.

If it’s cold:

Deep veins dilate, causing warmth from arterial blood to be diverted to deep vein and thus heat conserved as it returns to the heart.

Question 10

What is sensible heat?

Answer 10

Sensible heat is heat exchanged by a body or thermodynamic system that has as its sole effect a change of temperature.

The term is used in contrast to a latent heat, which is the amount of heat exchanged that is hidden, meaning it occurs without change of temperature. For example, during a phase change such as the melting of ice, the temperature of the system containing the ice and the liquid is constant until all ice has melted.

Sensible-heat loss is non-evaporative heat transfer to the environment.

Question 11

What are all the different types of sensible-heat loss?

Answer 11

Conduction

Convection

Infra-red

Evaporative

Panting

Question 12

What is heat loss by conduction?

Answer 12

• losing heat directly to surface
  eg. , animal in surgery on stainless steel table eg. animal lying on bedding

Question 13

What is sensible-heat loss by convection?

Answer 13

• exchange between animal’s outer surface & air
  eg. , thermal loss, thermal gradient due to wind

This is influenced by the animal’s surface area to volume ratio; NB larger animals have smaller surface area to volume ratios

Question 14

What is sensible heat loss from infra-red radiation?

Answer 14

Loss of heat from infra-red waves from animal.

IR is actually more of a source of heat gain for animals, from sun & atmosphere, ground & solid objects eg., tin roof if housed inside

Question 15

What is the difference between sensible-heat loss and evaporate heat loss?

Answer 15

Sensible heat loss is non-evaporative heat transfer to environment.

Evaporate heat loss is through the body surface (sweat glands) and respiratory system (oral mucosa).

Question 16

What are some ways animals can lose heat that isn’t sensible-heat loss (ie., not conduction, not convection and not IR-radiation)?

Answer 16

Evaporation - sweating

Panting

Urination/Defecation

Question 17

What is meant by thermoneutral zone?

Answer 17

The range of temperature in which a homeotherm can regulate its body temperature by adjusting heat loss at negligible energy cost.

Within the thermoneutral zone:

– Metabolic heat production and energy expenditure are minimal
– Most production processes are most efficient
– The animal is thermally comfortable.

Question 18

What is an animal’s low critical temperature (LCT)?

What is the high critical temperature (HCT)?

Answer 18

Low Critical Temperature:

The min. body temperature that can be tolerated by an organism. Below this temperature, the biochemical properties of cell structures, especially membranes, are altered, and reactions are slowed such that the organism cannot maintain its usual bodily functions and death may ensue. Below the LCT animals experience cold stress and potentially death. In cold stress, thermogenesis increases eg., shivering.

High Critical Temperature:

The max. body temperature that can be tolerated by an organism. When body temperature exceeds upper critical point, cellular components and process become disrupted, and the organism eventually dies. For most animals the upper critical temperature lies in the range 30–45°C. Beyond the UCT animals experience heat stress and potentially death. In heat stress, evaporative heat loss increases, eg., sweating.

Question 19

What are Group 1 Animals in terms of thermoneutral range?

Answer 19

Group I animals have a very narrow thermoneutral range

Heat production decreases as temperature increases. They just get too hot, so they need to start losing heat.

Sensible heat loss decreases as temp increases. They can’t lose enough via conduction and convection in high temperatures.

Evaporative heat loss increases as heat increases.

Pigs & Chickens are Group 1 animals.

Question 20

What are Group 2 animals in terms of thermoneutral range?

Answer 20

Group 2 animals have a wider thermoneutral range than Group 1 animals.

Evaporative heat loss increases significantly as temp increases (because horses can sweat, for example).

Think of cows, horses, sheep – cows & sheep lose a lot through their nasal mucosa and sweating through nose, while horses sweat. All of them lose heat through urination.