Thermoregulation in Endotherms (homeostasis chapter 3)

Question 1

Detecting temperature changes

Answer 1

• Peripheral temperature receptors are found in the skin and detect changes in surface temperature
• Temperature receptors in the hypothalamus detect the temperature of the blood deep in the body

Question 2

Principles of thermoregulation in endotherms

Answer 2

• Use internal exothermic metabolic activities to keep them warm
• Use energy-requiring physiological responses to help them cool down
• They also have passive ways of heating up or cooling down, to reduce the energy demands of their bodies
• Rely on both behavioural and physiological responses

Question 3

Vasodilation

Answer 3

1. Arterioles near the skin surface dilate when temperature rises
2. Vessels that provide a direct connection between the arterioles and venules (arteriovenous shunt vessels) constrict
3. Blood is forced through the capillary networks close to the skin surface
4. This increases radiation of heat from the skin and cools down

Question 4

Vasoconstriction

Answer 4

1. Arterioles near the skin surface constrict
2. Arteriovenous shunt vessels dilate
3. Very little blood flows through the capillary networks close to the skin surface
4. Little radiation takes place due to the warm blood being kept well below the skin surface

Question 5

Increased sweating and similar methods of cooling down

Answer 5

• Core temperature rises = increased rate of sweating
• The sweat spreads out on the surface of the skin and evaporates - heat is lost, cooling the blood below the surface
• Some animals open their mouths and pant - water evaporates off their tongues and they cool down
• Kangaroos and cats often lock their front legs to keep cool in high temperatures

Question 6

Reducing the insulating effect of hair or feathers

Answer 6

Body temperatures increase, leading the erector pili muscles in the skin to relax - as a result, hair or feathers will lie flat against the skin, which avoids trapping an insulating layer of air
*the opposite happens if animals are trying to keep warm - erector pili muscles constrict which pulls the hair or feathers erect

Question 7

Shivering

Answer 7

Rapid, involuntary contracting and relaxing of the large voluntary muscles in the body - metabolic heat from exothermic reaction warm up the body instead of moving it

Question 8

Anatomical adaptations of endotherms to keep them warm

Answer 8

• Small body parts (e.g. ears) to minimise SA:V ratio to reduce cooling
• Thick layer of insulating fat underneath the skin (e.g. blubber in whales and seals)
• Hollow hair (e.g. in polar bears) to trap a permanent insulating layer of air
• Black skin to absorb radiation from the sun
• Building up fat stores for hibernation (as well as building a well-insulated shelter and lowering their metabolic rate)

Question 9

Behavioural adaptation of humans

Answer 9

Wearing clothes

Question 10

Behavioural responses of animals

Answer 10

• Basking in the sun
• Pressing themselves to warm surfaces
• Wallowing in water or mud to keep themselves cool
• Digging burrows to keep warm/cool
• Hibernation or aestivation

Question 11

The physiological responses of endotherms to changes in the core temperature are the result of complex homeostatic mechanisms involving negative feedback control from the hypothalamus. There are two control centres:

Answer 11

1. Heat loss centre - activated when temperature of the blood flowing through the hypothalamus increases, sending impulses through autonomic motor neurones to effectors (skin and muscles) - responses triggered to decrease core temperature
2. Heat gain centre - activated when temperature of blood flowing through hypothalamus decreases, sending impulses through the autonomic nervous system to effectors (skin and muscles) - responses triggered to increase core temperature