Endotherms in hot environments; dissipation of body heat

Question 1

At high temperatures

Answer 1

little heat can be lost by conductance (the amount of heat lost by
conductance depends on the scale of the difference between body temperature and ambient
temperature).

Question 2

At ambient temperatures above body temperature,

Answer 2

heat will be gained from the environment
(by conduction from hot air, radiation from sun and rocks etc) and needs to be dissipated as
well as metabolic heat.

Question 3

Evaporative heat loss

Answer 3

s is the main way in which metabolic heat and
heat gained from the environment is lost.

Question 4

Camels are a good example of a mammal adapted to living in warm environments.
Adaptations include large size and thick fur

Answer 4

which reduce heat gain

Question 5

Large size (high
volume: surface area ratio)

Answer 5

cuts down the amount of heat gained from the environment.

Question 6

When supplied with plenty of water,

Answer 6

the camel dissipates heat by evaporation

Question 7

When water
is in short supply, heat storage becomes more important.

Answer 7

To conserve water, heat gained
during the day is stored (body temperature may reach 41oC) and lost at night by conduction
and radiation, without the use of water. The camel’s core temperature drops several degrees
below normal (as low as 34oC) during the night so that it starts the day with a heat deficit
allowing it to absorb more heat during the day without reaching lethal temperatures.
Smaller animals cannot gain heat for such a long time without overheating; antelope ground
squirrels, which live in deserts, return to their burrow every 8 minutes to cool down – again
without the use of water.

Question 8

Other adaptations include “heat windows”

Answer 8

areas of thinly furred, highly vascularised skin
from which heat can be lost by radiation, evaporation or conduction. For example: axilla
(armpits). Blood flow to these areas can be regulated depending on temperature, and heat
loss can be further regulated by changing posture.

Question 9

Evaporative cooling:

Answer 9

is the most effective way of removing excess heat, therefore there’s a close link between
water balance and temperature control in hot environments.

Answer 10

• Sweat glands (some mammals) extrude water onto skin
• Exhalant air from lungs: breathe through mouth; expose tongue; increase rate of air flow
  by panting (rapid, shallow breathing that increases evaporation form upper respiratory
  tract).
• Spread liquid (e.g. saliva- rats) on body surface

Question 11

Advantages of panting over sweating

Answer 11

• salts not lost
• provides own air flow (not dependent on wind)
• cools brain e.g. in gazelles, cooled venous blood from respiratory passages cools blood
  entering brain from the carotid artery in a heat exchange system. Brain may be 2-3
  o C
  lower than core body temperature. For example, after running, the core temp of a gazelle
  is 44oC, but its brain temperature is 41oC. This is important as nerve tissue is especially
  susceptible to heat damage

Question 12

Thermostatic regulation of body temperature;
s at various locations

Answer 12

n body both central and
peripheral including skin.