Transcript Thermoregulation

Thermoregulation
Homeostasis
Temperature Extremes
• Humans are subjected to vast
changes in environmental
temperatures
• Enzymes operate over a very
narrow range of temperatures
• Failure to control body
temperature can result in
physiological changes &
damage
• The body has several
mechanisms to maintain body
temperature
• Thermoregulation
Temperature
• Core temperature
– most important body temperature
– temperature of organs in major
cavities
– rectal temperature gives best
estimation
• Shell temperature
– temperature closer to surface
– skin & oral temperatures
Mechanisms of Heat Transfer
• Radiation
• Conduction
• Convection
• Evaporation
Evaporation
• water changes
from liquid to
vapor
Thermoregulation
Homeostasis
• Control Center
– preoptic area of
hypothalamus
• Receptors
– in skin
• Effectors
– eccrine sweat
glands & blood
vessels
Mechanisms for Heat Loss
• Skin receptors note
increase in
temperaturemessate
sent to preoptic nucleus
heat loss center (also in
the hypothalamus)
stimulatedsets off series
of events to produce heat
loss
• inhibition of vasomotor
centerperipheral
vasodilationwarm blood
flows to skin’s surface
• as skin temperatures rise,
radiation & convection
loses increase
• sweat glands are
stimulated increase
outputevaporative loss
increases
• respiratory centers are
stimulateddepth of
respiration increases
Mechanisms for Heat Gain
• Skin receptors notice that temperature is
droppingpreoptic nucleus is notificed
• heat loss center is inhibited
• heat gain center is activated
• sympathetic vasomotor center decreases blood
flow to dermis of skin
• vasoconstriction reduces heat loss by
radiation, convection & conduction
• blood returning from limbs is shunted into deep
veins
• Piloerector muscles are stimulatedhair
stands on endtraps air near the skin
Heat Gain
• If vasoconstriction cannot restore or maintain
core temperatureshivering thermogenesis
begins
• gradual increase in muscle tone which increases
energy consumption of skeletal muscle
throughout the body
• increases work load of muscles & elevates O2 &
energy consumptionproduces heat which
warms deep vessels to which blood has been
shunted by sympathetic vasomotor center
• can increase rate of heat generation by
400%
Heat Gain
• Non shivering thermogenesis
• long term mechanism for heat production
• sympathetic nervous system & thyroid hormone
produce an increase in metabolism
• Heat gain center stimulates adrenal medulla via
sympathetic ANSepinephrine is
releasedincreases rate of glycogenolysis (break
down of glycogen) in liver & skeletal
musclemetabolic rate increases
• preoptic nucleus regulates production of TRHthyrotropin releasing hormone by the hypothalamus
• TRH increases production of thyroxin by thyroid gland
• Thyroxin is a key hormone in control of metabolism