9 Temperature Regulation

Question 1

What is the range for normal body temp?

Answer 1

36-38˚C or 96.8-100.4˚F

Question 2

______ is considered hyperthermia, either from fever or exercise

Answer 2

38-40˚C (100.4-104˚F)

Question 3

Temps above _____ —> heat stroke, multiple organ failure and brain lesions

Answer 3

40˚C or 104˚F

Question 4

Temps between ___________ are considered mild hypothermia

Answer 4

34-36˚C or 93.2-96.8˚F

Question 5

Temps between _______ —> impairment of temperature regulation

Answer 5

30-34˚C (86-93.2˚F)

Question 6

Temps below ______ —> Cardiac fibrillation

Answer 6

29˚C (84.2˚F)

Question 7

Mean body temp is 37˚C (98.6˚F) but varies ~1-2˚C with…

Answer 7

Time of day/sleep-wake cycles

Ovarian cycle

Environmental extremes

Physical activity

Age

Fever

Question 8

Time when our body temp is the lowest

Answer 8

Just before waking

Question 9

When do you see spikes in body temp during the ovarian cycle?

Answer 9

At the time of ovulation (~Day 14-16)

Question 10

What are the four mechanisms of heat exchange?

Answer 10

Radiation (energy through a medium or space via electromagnetic radiation)

Conduction (transfer of thermal energy through solid matter)

Convection (the process of losing heat through the movement of air or water molecules across the skin)

Evaporation (water vaporizing from respiratory passages and the surface of skin)

Question 11

Energy only moves in what direction when it comes to heat exchange?

Answer 11

Down its thermal gradient, from hot to cold

Question 12

Examples of heat transfer via radiation

Answer 12

Sun, fireplaces, inanimate objects, living things

Radiative emission from the body is via infrared photons

~50% of heat may be lost from the body this way, mostly during conditions of low physical activity.

Question 13

______ is the transfer of heat between stationary objects (two solids or the body and STILL air)

Answer 13

Conduction

For humans, this is minor route of heat transfer to the environment but some organisms utilize conduction extensively.

Question 14

_____ requires movement of a medium (liquid or gas) inside or across the surface of the body

Answer 14

Convection

Rate of heat loss depends on rate of fluid movement (why rabbits have huge ears)

Rate of heat transfer between a body and moving air is lower than the rate between a body and moving water (wind chill effect)

Question 15

Heat lost due to energy required to go from liquid to gas

Answer 15

Evaporation

580 calories will evaporate 1g of H2O

Sweating is an adaptive response to take advantage of evaporative heat exchange

Some evaporation occurs in the respiratory tract

Question 16

How much water do we lose due to evaporation in phoenix?

Answer 16

2-3 liters/hour

Question 17

What is the different between eccrine and apocrine glands?

Answer 17

Eccrine over entire body, adrenergic stimulation, release clear odorless salty secretion

Apocrine in axial and genital areas, release thick excretion and odor comes from bacterial activity

Question 18

Sweating is _______ as air becomes saturated with water vapor (ie humid day)

Answer 18

Less effective

Question 19

Why does dehydration increase the risk of heat stroke?

Answer 19

It reduces the ability to perspire

Question 20

Majority of passive heat transfer is by…

Answer 20

CONVECTION in the vascular circulation

Very little by fixed tissue conductance

Requires a temp gradient

Question 21

______ more blood blows through the skin than is necessary for nutrition

Answer 21

20-30x

Skin blood perfusion can vary between 400-2500 ml/min

Vasodilation increases convective heat transfer and vasoconstriction decreases heat transfer

Question 22

Heat loss from the skin surface is via a combination of …

Answer 22

Evaporation, Radiation, and CONVECTION

Question 23

Why does 80˚F swimming pool water feel cooler than 80˚F air?

Answer 23

More heat is lost through water because it allows for more convection

Question 24

_____ receptors are sensitive to a narrow range of temperature

Answer 24

Warmth = narrow range (44-46˚C)

Question 25

_____ receptors respond to a wider range of temp

Answer 25

Cold (peaks at 24-28˚C)

Question 26

Central thermoreceptors in the hypothalamic _______ and abdominal organs measure core body temp

Answer 26

Preoptic Area (POA)

Sensitive to temp changes as small as 0.01˚C

Question 27

__________ hypothalamus stimulates heat dissipation

Answer 27

Anterior (rostral)

Parasympathetic response

Question 28

_______ hypothalamus stimulates heat production and conservation

Answer 28

Posterior (caudal)

Sympathetic response —> shiver, vasomotor commands, shut down of sweat glands, postural changes

Question 29

Temperature sensors in the _________ respond to cold temps

Answer 29

POSTERIOR hypothalamus

—> increased heat production and decreased heat loss

Question 30

Temperature sensitive neurons in the _______ respond to elevated blood temp

Answer 30

ANTERIOR hypothalamus

Decreased heat production and increased heat loss

Question 31

What’s the deal with the thermoneutral zone?

Answer 31

Minimal changes in metabolic rate can regulate core temp within the thermoneutral zone.

Extreme temps on either end require much more significant energy expenditures

Question 32

_______ signaling in the POA influences temperature-sensitive neurons to increase body temp

Answer 32

Lepton

Stimulation of ß-receptors in brown fat, activating decoupling enzyme (requires synergistic action of thyroid hormone)

Question 33

Excessive ______ can increase body temp

Answer 33

Catecholamines

Stimulation of a1-receptors in vascular smooth muscle reduces blood flow to the surface of the skin

Question 34

At rest we produce ______ watts of heat but during exercise we produce _______ watts

Answer 34

85 watts vs 1200 watts

Intense aerobic exercise could theoretically increase core temp by 1˚C every few min but we compensate with evaporative and convective heat loss increases

Question 35

_______ and _________ are greater in trained individuals

Answer 35

Sweat rate and skin blood perfusion

Question 36

Heat acclimation when changing environments requires…

Answer 36

Just a few days

Question 37

Infection causes macrophages to release ________.

Answer 37

Endogenous pyrogens

Cytokines cause release of prostaglandins in the organum vasculosum laminar terminalis (OVLT) of the hypothalamus where the BBB is absent

Prostaglandins stimulate the pre-optic area (POA) to determine the hypothalamic set point

Question 38

Aspirin targets the hypothalamus to decrease _________

Answer 38

Cyclooxygenase, which is required for prostaglandin synthesis