Temperature relations of endotherms

Question 1

Endotherms generate

Answer 1

their own heat

Question 2

Most endotherms are also

Answer 2

homeothermic (they regulate
their body temperature)

Question 3

Homeothermic endotherms (most mammals and birds) regulate
rates of heat production, gain and loss so as to maintain a relatively constant

Answer 3

core body
temperature of 37-41oC, depending on species. Temperature at the periphery is less
constant. They have a high basal metabolic rate (generating heat) and various heatconserving and heat-dissipating mechanisms.

Question 4

Temperature regulation at different temperatures
Over a certain range of environmental temperature, the thermoneutral zone,

Answer 4

no extra
energy is required to maintain body temperature; body temperature is mainly maintained by
changing heat conductance of the body surface, which requires very little extra metabolic
effort. The thermoneutral zone is bounded by the lower and upper critical limits.

Question 5

Outside this zone, metabolic rate must increase to maintain body temperature

Answer 5

either by thermogenesis at cold temperatures (zone of metabolic regulation, below lower critical
temperature (LCT)) or to increase evaporative cooling in the zone of active heat
dissipation, above the upper critical temperature (UCT).

Question 6

BMR

Answer 6

basal metabolic rate

Question 7

At ambient temperatures far below the LCT

Answer 7

thermogenesis is unable to replace body heat at
the rate at which it is being lost, and hypothermia sets in. At temperatures far above the
UCT, heat production and gain exceed the rate of heat loss and hyperthermia ensues.

Question 8

Temperature regulation at moderate temperatures (thermal neutral zone)

Answer 8

Adjust heat transfer (gain/loss from environment), e.g.
* adjust blood flow to periphery (vasomotor response)
* fluff hair/feathers (pilomotor response)
* postures to conserve/dissipate heat

Question 9

Temperature regulation at temperatures below critical

Answer 9

Increase heat production above basal levels (thermogenesis) by converting stored energy
reserves into heat

Question 10

Shivering

Answer 10

this involves groups of antagonistic muscles. The muscle contractions produce
no useful physical work but chemical energy from hydrolysis of ATP is released as heat.

Question 11

Non-shivering thermogenesis:

Answer 11

metabolism of fat to produce heat. Some mammals have
special stores of brown fat between neck and shoulders adapted for rapid massive heat
production. The heat thus produced is carried around the body by the blood

Question 12

Characteristics of brown fat:

Answer 12

• many mitochondria,
• fat-metabolizing enzyme systems
• many blood vessels – rapidly transfer heat to rest of body
• activated by sympathetic nervous system
• important in animals emerging from hibernation
• increases during cold-acclimation