Thermoregulation Flashcards
Thermoregulation
Process of maintaining core body temperature at a near constant value
Normothermia
36.2-37.6 de reefs Celsius
97-100 F
Hypothermia
Less than 36.2 C
Mild-34-36C (93.2-96.8F)
Moderate- 30-34C (86-93F)
Severe- less than 30C (less than 86F)
Accidental- left out in cold, fall into river or lake, not wearing enough clothes
Therapeutic- decreased perfusion with MI or injury; kept in mild hypothermia to slow down body processes because they use less oxygen
Hyperthermia
Greater than 37.6 C
Body temp rises with unchanged hypothalamic set point
Natural ability to get rid of heat is impaired
Environment can be too hot
Genetic- malignant hyperthermia
Drugs can cause- narcotics, anything that increases metabolic rate (e.g., amphetamines), some antibiotics, antihistamines
Hyperpyrexia
Extremely high temperature greater than 41.5 C
Hypothalamus
Controls physiological adjustments
Uses the negative feedback loop to help regulate temperature
Fever
Increase in hypothalamic set point where the negative feedback loop works to cool the body down with a higher temperature
Infants and toddlers
Increased risk for hypothermia
Lack ability to conserve heat and immature body processes
Have large body surface area compared to mass which is also why they dehydrate faster
Decreased subcutaneous fat which acts as an insulator
Unable to correct changes/dependent on caregivers- cannot put on more clothes or take them off
Rule of thumb: have one more layer of clothing than what adults need. EX: if an adult has a sweatshirt on, the infant should have a t-shirt and a sweatshirt
Elderly
Risk for hyperthermia
Sweat glands decrease- decreased ability to perspire and use evaporation to cool selves
Reduced circulation can cause peripheral problems
Decreased vasoconstrictive response to cold- they can get cold faster as they continue to dilate esp. if they are on meds that cause vasodilation
Reduced shivering response as the muscles don’t respond as well and are cold more often
Slower metabolic rate- cold more often
Reduced perception of heat and cold so they may not recognize when they are cold or hot
Other populations at risk
Low socioeconomic status- if they cannot afford heat or cooling systems, warm clothing, etc.
Homeless- no protection from the elements
Risk factor: cognition
Dementia may cause inability to recognize if it’s too hot or too cold. They may wander out into the elements without wearing proper clothing.
Substance abuse- alcoholics who are drunk may not notice the changes from the elements.
Risk factor: health condition
CHF & DM patients have poor perfusion and a decreased ability to vasoconstrict or vasodilate, peripheral neuropathies where they are unable to feel the hot or cold as much
Traumatic brain injury- any injury to the hypothalamus can be chronically hot or cold
Poor nutritional status- if not maintaining glucose levels, can cause problems with heat or cold if glucose is not being used to cause shivering, etc.
Risk factor: genetics
Malignant hyperthermia
Risk factor: recreational or occupational exposure
Skiing or working in the cold, construction workers, running, exercising in the heat, etc.
How we gain heat
BMR
Muscular activity
Hormones (e.g., thyroid hormone)
Dietary-induced thermogenesis (we eat a lot, we get warm)
Postural changes (can gain heat by curling up into a ball which provides less surface area to lose heat)
Environment (external heat)
How we lose heat
Radiation
Conduction
Convection
Evaporation
Muscles
Respirations
Heat production and conservation
Produced through metabolic activity:
Ingestion and metabolism of food will create heat and keep us warm.
BMR- the higher the BMR, the warmer we typically are.
Amount of heat is dependent on amount of food, physical activity, and hormone levels. With physical activity, the more active we are, the more we create heat and normal hormone levels.
Chemical thermogenesis:
Epinephrine will make us warm and great more heat.
Conservation through peripheral vasoconstriction:
Heat is conserved through peripheral vasoconstriction; if I take my blood and stick it centrally in my body, I have less available at the surface and less available to lose heat. This makes vasoconstriction a good heat conserved.
Radiation heat loss
Electromagnetic waves that emit heat from the skin surface to the air
More skin exposed, the more heat lost
Vasoconstriction or dilation can help hold onto or lose heat by making blood readily available or pulling blood centrally
Conduction heat loss
Heat travels through something solid with direct contact
EX: our body sits on something cool, looses heat to cooler surface. This cools the body down. This is why we put a warming blanket down for older adults or put infants in a warmer- so they do not lose heat to the surface of the bed
Convection heat loss
Loss of heat by air currents
The flow of heat from the body surface to cooler surrounding air. Eliminate drafts such as windows or AC to reduce heat loss by convection
Naturally happens with the more exposed skin
Warm air (from skin) rises, will go away from our skin and cool air will enter and replace the warm air. This happens even without drafts. If there are drafts, heat loss by convection increases
Vasodilation heat loss
More convection can happen with this
Evaporation heat loss
Perspiration creates energy
When a liquid is converted into gas, it requires energy. It will take energy heat from the skin to cause evaporation. It produces cooling. We can promote that by using convection which increases evaporation rates.
Muscle activity heat loss
When the body itself is too hot, muscle tone will decrease
This decreases BMR and decreases our heat
This explains when it’s too hot, you feel tired and don’t feel like moving. Moving takes effort because the body is decreasing muscle tone.
Respiration heat loss
With ambient, cool air, this air is breathed in, the body warms it, used it for energy, then exhales the warm air which can cool our body
This only works if the ambient air is cooler than our body temperature
