14. temperature regulation Flashcards
What factors help determine heat production?
- basal metabolic rate
- muscle activity
- thyroxin
- norepi/epi
- cellular chemical activity
- metabolism for digestion, absorption, food storage
What factors can affect the rate of heat loss?
- speed at which heat is conducted from core to skin
2. how fast heat is transferred from skin to surroundings
What is the primary function of skin and subQ tissue?
- skin insulators with high level of vasculature
2. vasculature can obtain 30% of Cardiac Output and regulate temperature
Is the respiratory system able to transfer heat?
yes, small amounts
Heat conduction to the skin is controlled by what factor?
- dilation or constriction with an 8x difference from one another.
What controls vasoconstriction?
- sympathetic system in response to core temperature and environmental temp.
What is radiation?
- heat loss via infrared rays
- occurs in all objects not at absolute 0
- heat radiates from high to low areas
What is conduction?
- heat loss
2. kinetic energy moves from area of high energy to low energy
If the ambient temperature is higher than skin temp, what happens in conduction?
- KE from the air is transferred to the skin and warms the skin
What is convection?
removal of heat from skin by using moving air currents
If the ambient temperature is lower than skin temperature, what happens with respect to conduction?
- KE of the skin is transferred to the ambient air, and the skin begins to cool
What significant factor allows water to cool more efficiently than air?
water has a higher specific heat
What is insensible perspiration?
- heat loss of 16-19 Cal/day
2. 600-700mL/day
Rank the mechanisms of heat loss from highest to lowest.
- radiation
- evaporation
- conduction to air
- conduction to objects
How can heat be transferred?
- radiation
- conduction
- convection
- evaporation
What are factors that will stimulate sweating?
- stimulation of anterior hypothalamus-pre-optic area
- cholinergic sypathetic nerves
- epi/norepi in circulation
What is precursor secretion?
- secretion similar to plasma without proteins
2. 142 mEq Na, 104mEq Cl
Strong stimulation of sweat glands results in what?
- large precursor secretion form
- low water reabsorption
- 50% NaCl
What areas of the brain affect body temperature?
- anterior hypothalamic pre-optic area
2. pre-optic area
How does the anterior hypothalamic pre-optic area affect body temperature?
- contain hot and cold sensors
- heat sensitive neurons activate 2-10x more with 10 degree increase of temp
- cold sensitive will increase firing rate when body temp cools
What happens if the pre-optic area is heated?
- blood vessel dilation
- profuse sweating
- inhibition of excess heat production
What happens if the pre-optic area is cooled?
- blood vessel constriction
- no sweating
- activate heat production mechanisms
What mechanisms will increase body heat?
- skin vasoconstriction
- piloerection
- shivering, metabolic pathways, thyroxin secretions
WHat brain region controls shivering?
- dorsomedial portion of posterior hypothalamus
How are the posterior hypothalamus and hypothalamic preoptic area similar?
- the anterior hypothalamic preoptic area receives inhibition signals from the heat center
How does shivering occur?
- alpha/gamma motor neurons fire arrhythmically to increase skeletal muscle tone
What is chemical thermogenesis?
heat generation from increased metabolism or sympathetic stimulation
What role does epi/norepi have with chemical thermogenesis?
- they uncouple oxidative phosphorylation in mitochondria
Is chemical thermogenesis related to brown fat?
yes, directly related
What is the major role of thyroxine?
- used for acllimization to the cold by increasing metabolism over period of weeks
Thyroxine is released by cooling the hypothalamic pre-optic area. What are the steps involved to increase the BMR?
- cold acts on hypothalamic preoptic area
- activates thyrotropin release in hypothalamus
- TSH is stimulated and released
- TSH increases thyroxine from the thyroid gland
- Thyroxine increases the BMR over period of weeks
What is body core temp?
37.1 degrees celsius. 98.8 fahrenheit
What is set-point control mechanism?
the level at which sweating or shivering begins to return to critical core temp.
What happens if core temp is below the set-point?
- post. hypothalamus activates heat-generating mechanism
What happens if teh core temp is above the set-point?
- post. hypothalamus activates heat loss mechanisms
What is feedback gain of temperature control?
- measure of the effectiveness of the temperature control system
How is the feedback gain of temperature control calculated?
divide change of environmental temp by body core temp change and subtract 1
What is Fever?
- body temperature that is above the usual range of normal
What is pyrogen?
- compound that increases the set-point of the hypothalamus
WHat are some examples of pyrogens?
- LPS
- IL-1
- prostaglandins
How do IL-1 and prostaglandins cause fever?
- increase the set-point
How does aspirin affect a fever?
- blocks the formation of cyclooxygenases which prevents prostaglandin formation
What effect will arachidonic acid have on fever?
- will increase, as it will transition to become prostaglandins
When is heat stroke most likely to occur?
- body temp reaches point of tissue damage
2. sweating is impaired
What are the symptoms of heat shock?
- dizzy
- vomitting
- Abd pain
- LOC
- delirium
What other aspect will cause the symptoms of heat shock seem to exacerbate?
- body will likely undergo circulatory shock due to fluid loss and electrolyte imbalance.
- contributing to factors of shock
At what point is temperature regulation completely lost, and impaired?
- lost below core temp 85
2. impaired below 94
What happens to the chemical heat production ability as core temperature drops?
- each 10 degrees reduces the ability of heat production 2fold
What is a common factor that will cause the body to lose its ability to shiver when cold?
- individual will become sleepy, and lose ability to shiver when asleep
What is heat exhaustion, and what causes it?
- caused by overexcessive sweating
2. syncope due to hypovolemia and hypotension
What is malignant hyperthermia and what causes it?
- caused by inhalation of anesthetics by susceptible persons
- rapid body temp rise due to increased oxygen consumption and rapid muscle firing
How does a person become hypothermic?
- ambient temperature is too low, that heat generating mechanisms are unable to maintain the core temp near the set-point.
What role is aldosterone used for in regards to sweating?
- helps to maintain normal levels of body salt. NaCl is lost via sweating and via urine, therefore increased levels of aldosterone will increase the amount of Na absorption which would occur during times of profuse sweating
In what type of scenario would an individual have increased levels of aldosterone, after changing climates?
- unacclimatized individual from cold to hot environment will have increased aldosterone serum levels as they will have to compensate for Na absorption that is being lost significantly from profuse sweating.
