Thermoregulation Flashcards
Metabolic rate for heat loss or gain
Gain heat
- Increase temperature increase metabolic rate
- Cold and start shivering to contract muscles and gain heat
Radiation for heat loss or gain
Both
- Radiating sun = heat gain
- Body radiates heat = heat loss
Conduction for heat loss or gain
Both
1. sit on cold bench = heat loss
2. Touch hot light bulb = gain heat
Conduction in water is greater than air because air is insulated
Convection for heat loss or gain
Heat loss and gain
As long as environment temp is below core temp, will lose heat due to convection opposite occurs when its hot
Evaporation for heat loss or gain
Heat loss through sweating and then having it evaporate
Facilitated by convection
What is the benefit of having mechanisms for heat gain and loss?
keep the bodies core temp in balance for homeostasis
What does heat exchange rely on?
Gradient between skin an the environment
What is the core temp?
37 degrees Celsius
What is the skin temp?
34 degrees Celsius
What is the primary mechanism for heat loss?
Evaporation
What occurs when can’t lose heat by evaporation?
- Higher core temp
2. Higher sweat rate
What is the bodies response when it is cold?
- Cutaneous vasoconstriction
- Pilorection
- Shivering
- Non-shivering thermogenesis (increase thyroxin release from thyroid)
What is the bodies response when it is hot?
- Cutaneous vasodilation
2. sweating and evaporation
Where is the thermoregulatory center?
hypothalamus
How is body temperature sensed?
- Central thermoreceptors
- Peripheral thermoreceptors
- Hypothalamus set-point
Central thermoreceptors
Located in pre-optic anterior hypothalamus (POAH)
More sensitive to heat and elicit VD reflex
Have an Ach cholinergic response
Peripheral Thermoreceptors
Distributed throughout the skin
More sensitive to cold and elicit VC reflex
Have an alpha adrenergic response
Neural control of cutaneous circulation with reflex mechanisms
It’s a dual sympathetic innervation
1. Sympathetic adrenergic receptors = vasoconstriction
2. Sympathetic cholinergic receptors = vasodilation
Also have local mechanisms
What catecholamine binds to adrenergic receptors?
Norepinephrine
What catecholamine binds to cholinergic receptors?
Ach
What is different about acral skin vs. non-acral skin?
Acral skin is not dually innervated just have sympathetic adrenergic innervation that causes vasodilation
What are the responses in non-acral skin when increase temperature in one area of the body?
- Passive vasodilation - remove sympathetic tone
- Active vasodilation - sympathetic cholinergic response is added
- Start sweating when cholinergic response is added
What happens to stroke volume in the heat?
decreases b/c lose plasma volume
What is the compensatory response when stroke volume decreases?
increase heart rate
Where is most of the blood when the body is in high temperature?
Periphery
Why does total periphery resistance decrease in the heat?
The vessels are vasodilating
What does dehydration do to the body?
Decrease CO steadily creating competition for blood flow.
- Active muscle keeps it the longest
- skin lose blood flow second and core temp starts to rise
- Inactive tissue (guts) first to lose blood flow for compensatory reasons
What beats the greedy bastards with dehydration?
Brain
What does angiotensin II cause during exercise?
Vasoconstriction which increases Blood Pressure
Stimulates thirst centers in hypothalamus
What does aldosterone cause during exercise?
sodium reabsorption at the kidneys
How much fluid should an athlete drink to maintain fluid homestasis?
Drink enough to match weight loss
How does dehydration impose a thermal and cardiovascular threat?
Become hypohydrated which leads to decrease sweating, decrease evaporation, decrease heat loss, increase core temp
Heat cramps
Na and K losses
Heat Exhaustion
Volume loss is more detrimental than high core temp
Treat with cooling, fluid, and electrolyte replacement
Heat Stroke
Brought on by heat exhaustion
Regulatory mechanisms are gone
Treat with rapid cooling
Heat injury prevention
- Recognize symptoms- headaches, chills, confusion
- Water availability
- Acclimatization
What is the significance of acclimation?
As the body is acclimatized decrease cardiac output and thermal strain while increasing sweat which increases evaporation and keeps body cool
Need to allow the body to increase plasma volume first couple of times in the environment