Thermoregulation Flashcards
What factors affect heat gain?
Exercise - 15-20% of expended, Nonexercise activity, Resting metabolism - 60-75% of expended, Hormone/CNS - thyroid makes T3 which increases O2 consumption and heat production, thermic effect or food - 10% expended, and Warm environments
What factors affect heat loss?
Conduction - heat is exchagned between direct contact, Convection - transfer of heat via movement of air or water, Radiation - transfer of heat in form of infrared rays between warm and cool object, and Evaporation - conversion of liquid to vapor
Best methods of cooling in order
Convection>Conduction>Radiation
heat moving down a concentration gradient
radiation
requires contact
conduction
movement of environment drags heat out of the body; sweat
convection
What’s normal body temp?
97-98.6 degrees
How does homeostatic control work?
If body temperature exceeds 37C, thermoreceptors sense, and preoptic/ anterior hypothalamus is activated. Posterior region activated by cold and anterior region activated by warmth
What are two types of thermoreceptors?
Peripheral sense surface temp and are part of skin, visceral structures, SP cord and central sense core temp are part of hypothalamus
What are dual mechanisms for controlling heat dissipation and conservation?
the heat dissapatory center is in preoptic/anterior hypothalamus and by stimulsting, you get dilated blood vessels, panting and inhibition to shiver. Heat conservation of posterior thalamus leads to vasoconstriction, visceral vasodilation, shivering
In hypothalamus and around spinal cord, viscera, and larger vessels. These monitor blood temperature
central receptors
Under the skin, senses temperature changes in the environment and provides feedback to hypothalamus and cerebral cortex, controls conscious acts like curling up when cold
peripheral receptors
sweating is driven by…
sympathetic post ganglionic neurons via ACh
Decrease in sympathetic vasoconstriction and activation of parasympathetics
vasodilation
What does sympathetic do when temperatures drop?
Activated by the hypothalamus, these neurons constrict arteries to keep warm blood away from cool skin, does metabolic heat production from brown adipose which uses uncoupled receptors, and increased secretion of TSH to bind B3 receptors on brown adipose
Behavioral responses that maximize heat loss
use of fans to increases convective heat loss, immersion in water to increase conductive heat loss, stay out sun to prevent radiant gain, removing clothes
What 3 mechanisms of hyporthermia?
Mild - (93.2-96.8) usually tachycardiac and high RR
Moderate - (86-93.2) decreased RR, HR, BP and decreased cerebral blood flow
Severe (less than 86) cardiac dysrhythmia like ventricular fibrillation, asystole, hypotension
Raynauds Syndrome
vasoconstriction of the digital arterioles of fingers/toes. These areas turn white because of constricted flow (hypoxia). Can be triggered by stress, cold temp, smoking
Hyperthermia
When temperature rises above 104° F (40° C). Unlike fever, it doesn’t respond to antipyretics, and can kill quickly. Caused by Excess heat production, excess heat from the environment, or impaired heat loss from the body and leads to higher oxygen demand so increased HR
What happens during heat stroke?
If your body compensates: activation of muscarinics leads to sweating, depletion of Na+ (hyponatremia), water depletion and exhaustion
If your body can’t compensate: proteins denature, organ failure, inflammation, BP drops, cardiovascular collapse, physical damage to vasculature
What happens during heat exhaustion?
Muscarinics lead to sweating, Na+ depletion, H2O loss, nausea, dehydration
What are some influencing factors of hyperthermia?
High body mass is associated with more sweating, Heat adaption improve sweating, aerobic fitness improve sweating, ages over 40 have reduced sweating, females have reduced sweating, diabetes can decrease heat loss, fatness can also increase heat production
excess calcium release from muscle triggered by depolarizing muscle relaxant succinylcholine and the inhalational anesthetic agent’s isoflurane, desflurane, sevoflurane, enflurane, halothane, ether, and methoxyflurane.
malignant hyperthermia
What is mechanism of malignant hyperthermia?
exposure to triggering agent that binds to mutated muscle receptor leading to increased Ca2+ release. Leads to sustained contraction, rigidity, metabolism which increase heat. There’s oxygen depletion and ATP, so CO2 produced leading to acidosis. Anaerobic metabolism increases acidosis, ATP depleted, cells die and release K+ resulting in hyperkalemia which causes dysrhythmia
What are 3 isoforms of RYRs?
RYR1 in adults, RyR2 in cardiac, and RyR3 in embryonic skeletal
What are body and rectal fever temperatures?
Body is >100.4 rectal is >101.8
Fever (pyrexia)
elevation in body temperature caused by a cytokine-inducing pyrogens, leading to upward displacement of the set point of the hypothalamic thermoregulatory center. Exogenous pyrogens microbial products, toxins or whole microbe.
Resolved when the factor responsible for set point increase is removed.
induce leukocytes and macrophages, to release fever-producing endogenous pyrogens (inflammatory cytokines)
Pyrogenic cytokines increase set point of the hypothalamus
Triggered by exogneous pyrogens
How do exogenous pyrogens lead to increase of endogenous pyrogens?
induce synthesis of PGE2 within the preoptic nucleus of the anterior hypothalamus, increases sympathetic activity, induces shivering, and impairing heat loss. 🡪 People with fever experience chills until the core body temperature rises to the new set point.
What targets production of pyrogenic cytokines?
corticosteroids
what inhibits cyclo-oxygenase?
Antipyretics such as aspirin which prevents more prostaglandin E2 production
What are four stages of fever?
- complaint of fatigue, malaise
- Chills, raising of hypothalamic set point, vasoconstriction, shiver
- vasodilation leads to flushed skin
- decrease in pyrogens or treatment, sweating, vasodilation
NSAID that blocks PGE production via cyclooxygenase inhibition, results in vasodilation, sweat
Ibuprofen
Fever vs. Hyperthermia
fever you feel cold where hyperthermia you feel hot, need to take physical measures to treat hyperthermia, elevated set point in fever, hyperthermia has high mortality
fever more than 106.7 (41.5)
Hyperyrexia which can develop in patients with severe infections or CNS hemorrhage
