Body Temperature Flashcards
homeothermic
maintaining a relatively constant body temperature, independent of the temperature of the surrounding environment
metabolism
makes use of mitochondria to produce energy
core temperature
warm, internal
shell temperature
cool, external
thermoregulation
ability to maintain a constant body temperature despite external temperature changes
temperature regulating centers located in the hypothalamus
mechanisms of heat exchange
used to maintain homeostasis when the body isn’t thermoneutral
radiation
transfer of heat without contact, from an object to its environment and visa versa via infrared rays
evaporation
transfer of heat due to evaporation of water
only way to regulate body temperature when external environment is >37*C
major heat loss mechanism
conduction
exchange of heat between objects of different temperatures that are in direct contact
convection
transfer of heat through circulation of air currents or liquid along the skin surface
heat loss
depends on the blood flow through the skin capillaries
promoted by vasodilation
metabolism
major source of internal heat generation
non-hypothalamic
shivering thermogenesis
skeletal muscle metabolism
somatic neurons activated
non-shivering thermogenesis
brown fat metabolism
SNS activated to release norepinephrine which activates the uncoupling protein for the mitochondrial and oxidative phosphorylation uncoupling
brown fat
used in response to cold as it has many mitochondria that can be used for energy (heat) production
heat conservation
vasoconstriction
piloerection
behavioral changes
anterior hypothalamus
heat loss center
warm-sensing neurons
excited by increase in temperature
stimulates sweating and vasodilation
posterior hypothalamus
heat gain center
cold-sensing neurons
excited by decrease in temperature
stimulates conservation, and shivering and non-shivering thermogenesis
thermoreceptors
sensory neurons monitor skin and core temperature then send information to the hypothalamus
peripheral thermoreceptors
found in the skin
central thermoreceptors
found in the hypothalamus, viscera, and veins
sympathetic nervous system
acts on smooth vascular muscle via vasomotor neurons to control vasodilation and vasoconstriction
AV shunts
short vessels that connect small arteries and small veins
cholinergic neurons
bind to acetylcholine which induces vasodilation and causes sweating
adrenergic neurons
bind to epinephrine and norepinephrine which induces vasoconstriction and causes heat conservation
activates cAMP
eccrine sweat glands
occur over most of the body
open directly onto the surface of the skin
apocrine sweat glands
open into hair follicles leading to the skin surface
hyperthermia
body’s temperature rises abnormally high without a change in set point
failure of heat regulating mechanisms - not able to lose heat
heat exhaustion
high core temperature (37.8-39*C)
severe dehydration due to sweating caused by vigorous exercise in hot humid climates
heat stroke
extremely high core temperature (>41*C)
fatal hyperthermia caused by heat exposure through environmental factors and physical exercise
heat cytotoxicity
cytokines released by heat-stressed cells cause local and systemic inflammation and multiple organ failure during heat stroke
malignant hyperthermia
autosomal dominant genetic disorder
abnormally elevated temperature (44.5*C max)
uncontrolled skeletal muscle contractions triggered by anesthetic agents
rhabdomyolysis
breakdown of muscle tissue releasing toxic protein (myoglobin) into the blood that results in kidney damage and brown urine which is a symptom of malignant hyperthermia
hypothermia
core temperature falls below 35*C
body fails to produce enough heat
hypothalamus cannot thermoregulate
mild hypothermia
32-35*C
shivering
increased pulse and breathing
dehydration
moderate hypothermia
28-32*C
decreased shivering
rigid muscles
decreased pulse and breathing
severe hypothermia
<28*C
coma
no pupillary reflex
slugging of RBCs
passive external rewarming
remove from cold
remove wet clothes
cover with blankets
supply warm fluids
active external rewarming
immerse in warm water
heat with air warmers
heating pads or hot water bottles
invasive active core rewarming
warm fluids pumped into stomach
extracorporeal blood rewarming**
inhalation of warm O2
warm IV fluids
frostbite
localized hypothermic injuries
tissue freezing
ice crystals form extracellularly causing cellular dehydration and shrinkage
microvascular blood flow occlusion leads to ischemia and thrombosis resulting in tissue damage
artificial hypothermia
induced artificially during surgery using sedatives (21-24*C)
fever/pyrexia
elevation of body temperature above normal (37-39*C) as a result of the hypothalamic thermostat being reset due to an immune response
pyrogens
fever reducing substances
exogenous pyrogens
not bodily derived
produced by pathogens
endogenous pyrogens
bodily derived
released in response to exogenous pyrogens
produced by leukocytes and macrophages
metabolic shift during fever
glucose is a bacterial growth medium so switch to protein and fat breakdown
prolonged fever results in fat loss due to high levels of ketones that lead to metabolic acidosis
antipyretics
drugs that lower fever by resetting the set point to lower or normal values
inhibits PGE2 production by inhibiting COX-2
