Temperature regulation

Question 1

Normal body temperature

Answer 1

37 degrees+/- 0.5

Question 2

What are normal variations in body temperature?

Answer 2

Person to person variations

Circadian rhythm

Menstrual cycle

Question 3

How do circadian rhythms affect body temperature?

Answer 3

Daily variation (0.5 degrees) with a minimum in early hours and peak in late afternoon

Question 4

How does the menstrual cycle affect body temperature?

Answer 4

Rise of 1 degree C after ovulation

Question 5

Above what temperature are proteins damaged?

Answer 5

42 degrees

Question 6

Energy expenditure falls …. for every 1 degree drop in core temperature

Answer 6

13%

Question 7

The thermoneutral zone is

Answer 7

The temperature range over which there is no “active” heat generation or loss

Question 8

Naked human thermoneutral zone

Answer 8

25-30 degrees

Question 9

What is a calorie?

Answer 9

Energy required to heat 1g of water by 1°C

Question 10

Thermogenic effect of food is?

Answer 10

Describes the heat generated by the chemical reactions of digestion, absorption and storage of food

Question 11

What food type increases BMR by the most (greatest thermogenic effect)?

Answer 11

Protein

Question 12

What hormone raises BMR?

Answer 12

Thyroid hormone

Question 13

How much can thyroid hormone increase BMR by?

Answer 13

50-100% above normal

Question 14

Total loss of thyroid secretion will decrease BMR by…

Answer 14

40-60% of normal levels

Question 15

What hormones other than TR have an effect on BMR?

Answer 15

Testosterone (~10-15% increase in BMR) and growth hormone (~15-20% increase in BMR)

Question 16

What activates BAT?

Answer 16

Low temperatures

Question 17

Two means of thermogenesis

Answer 17

Shivering and BAT

Question 18

How does BAT promote thermogenesis?

Answer 18

Rich in mitochondria and uncoupling protein 1 (UCP-1). Heat is generated through the dissipation of the proton gradient across the inner mitochondrial membrane via UCP-1

Question 19

Radiation

Answer 19

Results from the emission of a spectrum of electromagnetic radiation due to an objects temperature

Question 20

Convection

Answer 20

Removal of heat from the body by air currents

Question 21

Magnitude of convection heat loss depends on?

Answer 21

The movement of air over the surface of body

Conductive heat loss ∝ √wind velocity

Question 22

Conduction

Answer 22

Transfer of heat through direct contact with objects

Question 23

Why is conduction a small factor for heat loss in humans?

Answer 23

Air is a poor conductor

Question 24

Evaporation

Answer 24

Conversion of water from a liquid to a gas requires energy to overcome the latent heat of vaporization.

Question 25

Typical water loss per day (evaporation)

Answer 25

600-700ml

Question 26

Body Heat=

Answer 26

Metabolic heat production ±

Conductive, convective and radiant heat exchange − Evaporative heat loss

Question 27

In high temperatures, how do we lose heat?

Answer 27

evaporation is the only way to lose heat as conduction, convection and radiation all lead to heat gain.

Question 28

What parts of the hypothalamus function as a thermostat?

Answer 28

Preoptic and anterior hypothalamus operates as a thermostat for the body (with greater sensitivity to heat than cold).

Question 29

Do central temp regulators have greater sensitivity to hot or cold?

Answer 29

Hot

Question 30

Do peripheral temp regulators have greater sensitivity to hot or cold?

Answer 30

Cold

Question 31

Where are peripheral temp regulators located?

Answer 31

Spinal cord, abdominal viscera and great veins (deep body sensors) and the skin.

Question 32

How do peripheral receptors respond to changes in temperature?

Answer 32

Sensors respond to change in temperature by changing discharge frequency

Question 33

Where is central and peripheral sensor information combined?

Answer 33

Posterior hypothalamus

Question 34

Arteriovenous shunts allow?

Answer 34

Blood supply to the periphery to be controlled

Question 35

How are shunts centrally mediated?

Answer 35

alpha-1-adrenergic receptors

Question 36

Shivering can increase heat production by %?

Answer 36

200%

Question 37

Exercise induces heat production increase by how many fold?

Answer 37

10 fold

Question 38

What is shivering?

Answer 38

Rapid (~50Hz) and unsynchronized muscular activity

Question 39

How is shivering centrally controlled?

Answer 39

Signalled from the posterior hypothalamus and translated to the anterior motor neurons

Question 40

What fibres lead to production of sweat?

Answer 40

Cholinergic sympathetic nerve fibres elicit the secretion of a primary fluid into the sweat duct.

The glands can also be stimulated by adrenaline/noradrenaline (e.g. during exercise)

Question 41

Is sweat reabsorbed?

Answer 41

Yes, some along the duct

Question 42

Light sweat is consistent of? Why?

Answer 42

Concentrated solution of urea, lactic acid and potassium

Water, NaCl reabsorbed

Question 43

How much sweat can be produced by athletes?

Answer 43

Up to 2L/hour

Question 44

Hypothermia arises when

Answer 44

Continued exposure to cold temperatures causes the core body temperature to drop below 35°C

Question 45

Loss of consciousness at what temperature?

Answer 45

30 degrees

Question 46

Why are neonates susceptible to hypothermia?

Answer 46

Reduced behavioural adaptations and greater surface area to volume ratio (although they do possess BAT for thermogenesis)

Question 47

What causes hyperthermia?

Answer 47

Pyrogens (LPS or cytokines)

Elevate prostaglandin E2 synthesis in the hypothalamus

Question 48

Infection can lead to..

Answer 48

Elevation in the regulatory set-point of core body temperature

Question 49

Heat exhaustion/heat syncope occurs due to

Answer 49

Hypovolaemia from excessive sweating

Question 50

Heat stroke occurs when?

Answer 50

Body temperature is greater than 40.6 degrees