5.1.4 temperature control in endotherms

Question 1

hypothalamus

Answer 1

part of brain which coordinates homeostatic responses

Question 2

what does temp regulation rely on

Answer 2

• effectors in skin & muscles
• skin = organ in contact with external environment
• many of physiological adaptations to control body temp involve skin = alter heat loss to environment

Question 3

what are many chemical reactions in the body

Answer 3

exergonic = release energy in form of heat

Question 4

skin: response if body too hot

Answer 4

• sweat glands secrete fluid onto surface which evaporates = uses heat from blood as latent heat of vaporisation
• hairs/feathers lie flat = reduces insulation & allow heat loss
• vasodilation of arterioles/pre-capillary sphincters = directs blood to skin surface so heat radiated away from body

Question 5

skin: response if body too cold

Answer 5

• less sweat secreted = less evaporation so less heat lost
• hairs/feathers stand erect to trap air = insulates body
• vasoconstriction of arteries/pre-capillary sphincters leading to skin surface = blood diverted away from skin surface so less heat loss

Question 6

gaseous exchange system: response if body too hot

Answer 6

• some animals pant = increase evaporation of water from surface of lung/airways
  –> evaporation uses heat from blood as latent heat of vaporisation

Question 7

gaseous exchange system: response if body too cold

Answer 7

• less panting = less heat lost

Question 8

liver: response if body too hot

Answer 8

• less respiration occurs = less heat released

Question 9

liver: response if body too cold

Answer 9

• increased respiration in liver cells = more energy from food converted to heat

Question 10

skeletal muscles: response if body too hot

Answer 10

• fewer contractions = less heat released

Question 11

skeletal muscles: response if body too cold

Answer 11

• spontaneous muscle contractions (shivering) = release heat

Question 12

blood vessels: response if body too hot

Answer 12

• dilation to direct blood to extremities = more heat lost

Question 13

blood vessels: response if body too cold

Answer 13

• constriction of blood flow to extremities = blood not cooled much
  –> frostbite (extreme conditions)

Question 14

physiological/behavioural adaptations of endotherms if too hot

Answer 14

• hide away from sun in shade/burrow
• orientate body to reduce SA exposed to sun
• remain inactive/spread limbs out = greater heat loss
• wet skin to use evaporation to help cool body (eg. cats lick themselves, elephants spray water over bodies)

Question 15

physiological/behavioural adaptations of endotherms if too cold

Answer 15

• lie in sun
• orientate body towards sun to increase SA exposed
• move about to generate heat in muscles –> extreme = roll into ball to reduce SA & heat loss
• remain dry

Question 16

advantages of endothermy

Answer 16

• maintain fairly constant body temp whatever external temp
• remain active even when external temp low = take advantage of prey available/escape predators
• inhabit colder parts of planet

Question 17

disadvantages of endothermy

Answer 17

• use significant part of energy intake to maintain body temp in cold
• need more food
• use for growth a lower proportion of energy & nutrients from food
• may overheat in hot weather

Question 18

describe control of temperature regulation

Answer 18

1. temperature receptors in hypothalamus of brain detect change
2. sends out impulses causing different responses to reverse change
3. some responses must be quick to prevent further change = neuronal system outputs impulses so rapid responses
4. some responses longer term = hormonal system transmits output for these

Question 19

what changes will the hypothalamus bring about if the core temp is too low

Answer 19

• changes in skin to reduce heat loss
• release of heat via extra muscular contraction
• increased metabolism to release more heat from exergonic reactions

–> opposite changes if core temp too high = eg. of negative feedback

Question 20

role of peripheral temperature receptors

Answer 20

• early warning of change in body temp = help hypothalamus respond quicker
• if extremities start to cool down/warm up = eventually affect core body temp
• obtain peripheral temperature receptors in skin which monitor temp in extremities
• info fed to thermoregulatory centre in hypothalamus
• brain can initiate behavioural mechanisms