15.3 Thermoregulation In Endotherms

Question 1

Describe thermoregulation in endotherms

Answer 1

• they control their body temperature internally by homeostasis, as well as by altering their behaviour
• less affected by external temperature

Endotherms have a constantly high metabolic rate because they can keep their internal temperature constant. They are active at any temp.
They generate a lot of heat from metabolic reactions.

Question 2

State physiological responses when core body temperature is increased, so the animals needs to cool down

Answer 2

• vasodilation
• increased sweating
• hairs lie flat

Question 3

Describe vasodilation

Answer 3

The arteriole near the surface of the skin dilate when temp rises
The vessels that provide direct connection between the arteriole and the venules (the arteriovenous shunt vessels) constrict.

This forces blood through capillary networks close to the surface of the skin.
The skin flushes, and cools as a result of increased radiation. This increases heat loss by radiation

Question 4

Describe the response of increased sweating

Answer 4

More sweat is secreted from sweat glands when body’s tooo hot
The water in sweat evaporates from the surface of the skin and takes heat from the body, cooling the skin

Question 5

Describe the response of hairs lie flat

Answer 5

Increased body temp causes erector pili muscles to relax so the hairs lie flat. Less air is trapped, so skin is less insulated and heat can be lost more easily.

Question 6

State physiological mechanisms to a decrease in temp, so that the animal needs to warm up

Answer 6

• vasoconstriction
• decreased sweating
• Hairs stand up
• shivering

Question 7

Describe vasoconstriction

Answer 7

The arteriole near the surface of the skin constrict.
The atriovenous shunt vessels dilate , so very little blood flows through the capillary networks close to the surface of the skin.
The skin looks pale. Reduced radiation means reduced heat loss.

Question 8

Described effect of decreased sweating

Answer 8

• this reduced cooling by the evaporation of water from the surface of the skin

Question 9

Describe effect of raising the body hair (or feathers for birds)

Answer 9

• the erector pili muscles contract, pulling the hairs of the animal erect
  This traps an insulating layer of air and so reduces cooling through the skin, prevents heat loss

Question 10

Describe effect of shivering

Answer 10

When it’s cold, muscle contract in spasms.
This makes body shiver and more heat is produced from increased respiration (metabolic heat from an endothermic reaction) increasing the core body temperature

Question 11

State additional anatomical or behavioural adaptions endotherms may have to help them keep warm

Answer 11

• adaptions to minimise ther SA;V ratio to reduce cooling (e.g. small ears)
• thick layer of insulating fat underneath the skin, e..g blubber in whales and seals
• some animals hibernate - build up fat stores, build a well-insulated shelter , and lower their metabolic rate so they can pass the cold weather in winter
• dark skin absorbs more radiation from Sun

Question 12

Describe and explain the control of body temperature by the hypothalamus

Answer 12

Body temp in mammal is maintained at a constant temp by the hypothalamus
The hypothalamus receives information about both internal and external temperature from thermoreceptors:

• thermorecpetors in the hypothalamus detect intern temp (temp of the blood)
• thermoreceptors in the skin (peripheral thermorecpetors) detect external temperature (temp of skin)

Thermorecpetors send impulses along sensory neurones to the hypothalamus, which sends impulses along motor neurones to effectors (e.g. erector pili muscles, sweat glands)

The effectors respond to restore the body temperature back to normal