Thermoregulation Flashcards
Homeotherm
animals that regulate internal temp for optimal biochemical reaction rates
Circadian rhythm temperature swings
lowest in morning and highest in evening
Homeostasis
balance of heat generation and heat dissipation
Why does metabolic transformations generate heat
inherent inefficiency (20% efficient and 80% heat release)
Resting metabolic rate
metabolic rate necessary to maintain function - adds to metabolic heat production (increased by thyroxin and EPI)
Thermal neutral environment
environment that a naked body would not lose nor gain heat
Avenues for heat transfer form the body
Conduction, convection, radiation, and evaporation
Conduction
heat transfer b/w 2 SOLID OBJECTS (ice pack)
Convection
fluid carries heat b/w body and environment (air, water)
Radiation
exchange occurs in the infrared portion of the EM energy spectrum (gain: surrounding objects have higher surface temp than body; loss: surrounding objects have lower surface temp than body)
Evaporative
phase change from liquid to gas (berthing, perspiration) INDEPENDENT of the thermal gradient b/w body and environment; DEPENDENT on water vapor pressure b/w skin and environment (humidity)
Balance of het production and heat loss
M (metabolic heat) - R - C - E = S (stored heat/current temp)
Physiological response to heat transfer
heat production (shivering), heat distribution (vasoconstriction), sweating
Negative feedback loop for thermal regulation
thermal sensors, hypothalamic integrative center and thermal effector
Thermal sensors
free-nerve endings cutaneous and hypothalamic thermal sensors to heat and cold
Hypothalamus and thermal regulation
skin and hypothalamic thermal receptor information is compared to “set point” and efferent thermal commands are send to re-establish set-point
Anterior hypothalamus is in charge of
decreases in body temp
Posterior hypothalamus is in charge of
increased in body temp
Thermal effectors
autonomic nervous system via vasoconstriction or vasodilation, stimulation of eccrine sweat glands, shivering, brown adipose activation
eccrine sweat glands
sympathetic cholinergic fibers for evaporative heat loss
What happens to the thyroid gland during thermoregulation
too hot = decreased thyroid stimulation = decreased metabolic activity
Hyperthermia
increased environmental temperature and humidity (heat index) reduces the body’s ability to loss heat through radiation, convection, and evaporation
Exposure to high temp and exercise
heat exhaustion and heat stroke
Risk factors for hyperthermia
lack of acclimatization, low fitness, obese, dehydrated
Malignant hyperthermia
genetic abnormality of skeletal muscle reaction to anesthetics (halothane or succinylcholine)
Treatment for hyperthermia
cold compresses and IV to rehydrate
Hypothermia
exposure to prolonged low temperatures, immersion in cold water, and wind bursts that increase het loss by conduction and convection
Reaction to hypothermia
shivering, increased muscle tone, vasoconstriction, Brown adipose tissue activity
Thermoregulation and exercise
Initially exercise increases core temperature because heat production > heat dissipation; heat loss mechanisms are activated and temperature plateaus at an elevated steady-state
What happens to the O2 dissociation curve during exercise
increased body temperature cause shift to the right, facilitating O2 unloading into peripheral tissues
Why is exercising in the heat potentially fatal (other than inability to release body heat)?
vasodilation to reduce body temp causes a decrease in the return venous flow to the heart, decreasing CO, heart pumps harder and faster to maintain CO (blood flow to viscera decreases = nausea) eventually decreased BV results in dizziness and fatigue
Heat acclimatization and physical training
trained individuals sweat earlier and more profusely and contains less Na ( increased evaporative heat loss reduced the need for conductive heat loss (vasodilation) maintaining high BV for circulation
Fever and body temp elevation
hypothalamus actively elevates core temp setpoint
Pyrogen
any substance that causes a fever
Prostaglandin E2 are elevated
elevation of PGE2 in the hypothalamic tissue increases the set-point for core temp and remains elevated until the pyrogen subsides
