Thermoregulation

Question 1

hypothalamus

Answer 1

• temperature “HQ” for the body in the brain
• controls involuntary mechanisms to keep core temp 36.1-37.8C
• very sensitive to small degree changes
• behaviour or physiological forms of thermoreg

Question 2

thermoregulation input

Answer 2

• hypothalamic temperature and other deep temperature contribute to core temp&raquo_space; thermal error signal
• pyrogens, heat acclimatization and exercise&raquo_space; set temp > thermal error signal

Question 3

behavioural thermoregulation

Answer 3

The maintenance of a constant body temperature by means of basking, sheltering, shivering, etc.
- thermal comfort and effector signal head to the brain

Question 4

physiological thermoregulation

Answer 4

effector signal for heat production > skeletal muscles
effector signal for sweating, vasodilation > arteries, sweat glands
effector signal for vasoconstriction > veins, arteries

Question 5

thermal receptors

Answer 5

central: hypothalamus and cortex receptors in brain
peripheral: skin receptors for hot and cold (shell)
deep (core): in abs and great veins can sense internal changes

Question 6

thermal effector responses to heat

Answer 6

• general peripheral vasodilation
• increase sweating to promote evaporation
• conscious acts (remove clothes, seek shade)
• acclimatation

Question 7

thermal effector responses to cold

Answer 7

• general peripheral vasoconstriction
• shivering and non-shivering thermogenesis (increase metabolic heat production)
• goose bumps (piloerection)
• conscious acts (move into sun, put on more clothes)
• acclimatation

Question 8

core temperature

Answer 8

rectal, tympanic (ear), oral, telemetric thermal pills
- rectal and GI are best (expensive)
- oral: lower than rectal (breathing and respiratory cooling)

skin temp: skin thermistors
- accuracy depends on location, exposure, movement

Question 9

thermal balance

Answer 9

heat loss/gain mechanisms need to be balanced to prevent pushing too far from 37C

gain: environmental (radiate, convection, conduction) and metabolic (BMR, thermogenesis, muscular activity)

heat loss: evaporation, conduction, convection, radiation

Question 10

radiation

Answer 10

transfer of heat btwn 2 objects via energy waves (electromagnetic)
- heat goes from warm object to cold object
- body can gain heat radiantly from the sun
- 60% of heat loss at rest

Question 11

conduction

Answer 11

transfer of heat btwn solid, liquid, gas molecules or different temp that are in direct contact
- ex: ice lying on hot stove
- related to temperature differences btwn objects
- 3% heat loss at rest

Question 12

convection

Answer 12

transfer of heat from one place to another by the movement of air/fluid across the skin
- related to velocity and temperature of the air/fluid flow
- 10% of heat loss at rest

Question 13

evaporation

Answer 13

transfer of heat when a liquid changes to a gas or vapour
- best cooling mechanism (25% heat loss at rest, room temp)
- latent heat of vaporization
- air humidity determines if heat > gas vs vapour
- dripping sweat is not evaporation (1L = 580cal)

Question 14

heat exchange factors

Answer 14

major determining factors for how well heat moves btwn body and environment
- thermal gradient
- relative humidity
- air movement
- degree of direct sunlight
- clothing worn

Question 15

important degrees

Answer 15

42+ C = seriously impaired (heat stroke, brain lesions)
40-43C = exertional heat stress
38-41C = effective fever in health (fever in exercise)
32-35C = mild hypothermia (the “-umbles”)
29-34C = impaired functioning
26-30C = severe hypothermia
less than 28C = lost functioning

Question 16

measuring heat stress

Answer 16

wet bulb globe temperature (WBGT)
- measure of heat loss in direct sunlight
- temperature, humidity, wind speed, sun angle, cloud cover

Question 17

body temperature during exercise in heat

Answer 17

• lower intensity means for lower core temp
• environmental conditions increase in intensity makes it harder to remain same core temp so it will increase
• “uncompensable zone” when core temp rapidly increases

Question 18

cardiovascular system in the heat

Answer 18

• blood flows to skin rather than muscles
• vasodilation to skin = less CBV = less venous return = less SV
• sweating decreases BV and SV thus a less Q (more CV strain)
• higher HR and lower preload = smaller CO
• Qmax less = VO2max less

Question 19

Spectrum of EHIs

Answer 19

mild: heat cramps (mild dysfunction)
mild/mod: syncope (multisystem, moderate dysfunction)
mod: heat exhaustion (multisystem, severe dysfunction)
mod/severe: heat injury (multisystem damage)
severe: heat stroke (multisystem damage)

Question 20

cardiovascular drift

Answer 20

gradual increase in HR during prolonged steady-state exercise
- rising body temp (sensed by hypothalamus)
- vasodilation of skin leads to less central blood volume
- dehydration = less BV = less preload = less SV = higher HR to maintain Q

Q = SV x HR (if one decreases the other increases to maintain Q)

Question 21

importance of fluid ingestion

Answer 21

• Q will increase as hydration does
• SV is higher with better hydration
• HR is lower with better hydration
• can combat CV drift

Question 22

factors affecting response to heat stress

Answer 22

acclimatization - adjustments made to repeated exposure
fitness level - better trained = better thermoregulators
body composition - more fat = more insulin
hydration levels -

Question 23

heat acclimatization

Answer 23

in as early as 1-4 days, full acclimatization in 10-24 days
circulatory: more plasma volume = higher Q (less CV strain)
and more blood flow from periphery to core

sweat: start to sweat sooner, increase sweat rate w/o electrolytes lost

hormonal: altered ADH (urine) and aldosterone (electrolytes in kidney) (they tell kidney how much fluid to take)
- training will do 50-60% of the adaptations

Question 24

fluid ingestion

Answer 24

in most cases plain water is the best, except for endurance (>1hr) events where CHO drinks (2.5-10%) are recommended
- determined by gastric emptying and intestinal absorption
- Na, Cl, K are sweat electrolytes
- hyponatremia ( too much water intake dilutes Na (action potentials))

Question 25

exercise in the cold

Answer 25

hypothermia is less common in exercise except for in swimmers.

frost bite is bigger concern - treat with proper clothing, watch windchill, stay hydrated

Question 26

physiological responses to cold

Answer 26

non shivering thermogenesis (increase in SNS release EP = increase cell metabolic heat production = increase EE) (adrenaline from adrenal glands and thyroid boost heat production)

involuntary shivering: CNS attempt to increase metabolic het production = increase EE

goose bumps (add insulating layer, better in furry animals)

immersion diuresis (submerged)

Question 27

cold water immersion

Answer 27

cold shock phenomenon: gasp, hyperventilate increase VE 600-1000% (keep head up, do not panic; 1st min is critical)

cold incapacitation: 10 minutes of meaningful movement, drown after if w/o PFD

hypothermia: ~1hr before lose LOR depending on body comp

Question 28

acclimatization to cold

Answer 28

• initial effect over 7 days
• decrease in skin temp of when to start shivering
• increase non shivering thermogenesis (thyroxine hormone)
• cold induced vasodilation of hands and feet (less constriction)
• increased amounts of brown adipose tissue (BAT)

Question 29

brown fat

Answer 29

a dark-colored adipose tissue with many blood vessels, involved in the rapid production of heat in hibernating animals and human babies.