9 Temperature Regulation Flashcards
What is the range for normal body temp?
36-38˚C or 96.8-100.4˚F
______ is considered hyperthermia, either from fever or exercise
38-40˚C (100.4-104˚F)
Temps above _____ —> heat stroke, multiple organ failure and brain lesions
40˚C or 104˚F
Temps between ___________ are considered mild hypothermia
34-36˚C or 93.2-96.8˚F
Temps between _______ —> impairment of temperature regulation
30-34˚C (86-93.2˚F)
Temps below ______ —> Cardiac fibrillation
29˚C (84.2˚F)
Mean body temp is 37˚C (98.6˚F) but varies ~1-2˚C with…
Time of day/sleep-wake cycles
Ovarian cycle
Environmental extremes
Physical activity
Age
Fever
Time when our body temp is the lowest
Just before waking
When do you see spikes in body temp during the ovarian cycle?
At the time of ovulation (~Day 14-16)
What are the four mechanisms of heat exchange?
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)
Energy only moves in what direction when it comes to heat exchange?
Down its thermal gradient, from hot to cold
Examples of heat transfer via radiation
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.
______ is the transfer of heat between stationary objects (two solids or the body and STILL air)
Conduction
For humans, this is minor route of heat transfer to the environment but some organisms utilize conduction extensively.
_____ requires movement of a medium (liquid or gas) inside or across the surface of the body
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)
Heat lost due to energy required to go from liquid to gas
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
How much water do we lose due to evaporation in phoenix?
2-3 liters/hour
What is the different between eccrine and apocrine glands?
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
Sweating is _______ as air becomes saturated with water vapor (ie humid day)
Less effective
Why does dehydration increase the risk of heat stroke?
It reduces the ability to perspire
Majority of passive heat transfer is by…
CONVECTION in the vascular circulation
Very little by fixed tissue conductance
Requires a temp gradient
______ more blood blows through the skin than is necessary for nutrition
20-30x
Skin blood perfusion can vary between 400-2500 ml/min
Vasodilation increases convective heat transfer and vasoconstriction decreases heat transfer
Heat loss from the skin surface is via a combination of …
Evaporation, Radiation, and CONVECTION
Why does 80˚F swimming pool water feel cooler than 80˚F air?
More heat is lost through water because it allows for more convection
_____ receptors are sensitive to a narrow range of temperature
Warmth = narrow range (44-46˚C)
_____ receptors respond to a wider range of temp
Cold (peaks at 24-28˚C)
Central thermoreceptors in the hypothalamic _______ and abdominal organs measure core body temp
Preoptic Area (POA)
Sensitive to temp changes as small as 0.01˚C
__________ hypothalamus stimulates heat dissipation
Anterior (rostral)
Parasympathetic response
_______ hypothalamus stimulates heat production and conservation
Posterior (caudal)
Sympathetic response —> shiver, vasomotor commands, shut down of sweat glands, postural changes
Temperature sensors in the _________ respond to cold temps
POSTERIOR hypothalamus
—> increased heat production and decreased heat loss
Temperature sensitive neurons in the _______ respond to elevated blood temp
ANTERIOR hypothalamus
Decreased heat production and increased heat loss
What’s the deal with the thermoneutral zone?
Minimal changes in metabolic rate can regulate core temp within the thermoneutral zone.
Extreme temps on either end require much more significant energy expenditures
_______ signaling in the POA influences temperature-sensitive neurons to increase body temp
Lepton
Stimulation of ß-receptors in brown fat, activating decoupling enzyme (requires synergistic action of thyroid hormone)
Excessive ______ can increase body temp
Catecholamines
Stimulation of a1-receptors in vascular smooth muscle reduces blood flow to the surface of the skin
At rest we produce ______ watts of heat but during exercise we produce _______ watts
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
_______ and _________ are greater in trained individuals
Sweat rate and skin blood perfusion
Heat acclimation when changing environments requires…
Just a few days
Infection causes macrophages to release ________.
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
Aspirin targets the hypothalamus to decrease _________
Cyclooxygenase, which is required for prostaglandin synthesis
