Temp Regulation Flashcards
Body temp
Rate of heat production close to BMR
Resting is 80 kcal/hr
Increase 6-8 x during strenuous physical activity
Heat gain- metabolism, heat absorbed
Heat loss- environment
Core body temp= 37 C +/- 0.5
Body Core
Central heat compartment
Includes most viscera
Site of basal metabolism (heat gain)
Core temp is tightly reg
Body reg core body temp
Body shell
periphery of body
includes skin
insulates core from environment
Main site of heat loss
Extends several cm under the skin in cold environment
Heat Transfer
Radiation- surfaces of all objects constantly emit heat in form of electromagnetic waves.
Conduction- transfer of heat bt 2 stationary bodies in contact. Loss/gain transfer of thermal E during collisions of molecs
Convection- transfer of heat resulting from movement of fluid either a liquid or a gas. Aided by movement of air or water next to the object. Aids conduction exchange of heat by maintain supply of cool air
Evaporation- process by which H2O is transformed from liquid to gas state following E & heat release
Heat Transfer
Heat generated by skeletal m. transferred to body by convection
Blood transfers heat to environment when reaches skin
Skin utilizes conduction b/t 2 bodies until reach same temp
As air moves over surface of skin, heat carried away. Or water.
Heat Transfer
Evaporation- environment hotter than body but limited by humidity of air. (high humidity, not going to happen)
radiation- warmer to cooler body, at rest 60%,
Arteriovenous countercurrent
Warm blood from body core enters a. supplying an extremity, venous blood returning from shell is slightly cooloer
Temp gradient permits heat to transfer from a. to v.
As arterial blood progresses distally, constant temp gradient permits gradual cooling of arterial blood & conservation of heat w/in venous blood.
By this means, venous blood rentering core is back to nomral body temp w/ minimal loss of heat.
Greater interaction, greater heat transfer
Body Temp control
- feedback
sensor in skin & core
set pt 37C
Integration center0 hypothal
Effectors- skin blood flow, sweat production, shivering.
Sensors
R on skin & in hypothal that monitor temp. Both skin & hypothal R are free n. endings
Skin R provide hypothal info about temp & act as early warning sys. More cold R
R in hypothal monitor core temp where more warm R
Changes in core temp that initiate thermal reg responses not changes in skin temp
Temp Sensing
Integration center- hypothal. Periph thermoR & from central thermoR.
Ant nuke neurons- warm sensitive
post- cold sensitive
Voluntary, semi voluntary and involuntary
Set pt- 37 C w/in 36 to 38 range
Hyperthermia above 40 = heat stroke & brain lesions
Extereme hypothermia- below 34, impair thermal reg & cardiac arrhythmias. Raised by pyrogens (fever producing substances)
Temp Homeostasis & Effector sys
sweating
cutaneous blood flow
activity & posture
shivering
external covering
Elevation in core temp- increase in skin BF & sweating. Behavior activities occur (seeking shade, cold drink etc. )
Fall in core temp- skin BF & sweating is red, shivering thermogenesis may be initiated.
Eccrine Sweat Glands
Eccrine- mostly dilute electrolyte solution
Apocrine- also fat
Upon n. stimulation, isotonic fluid released from secretory (clear) cells into lumen of coil. As this fluid passes along duct to skin surface, ionic composition is modified by transporters in epitch cells lining duct.
Low sweat rates, more salt removed
Fluid leaving duct is hypotonic to plasma w/ 5-60 mmol/L of Na+
Activity of transporters & salt [] of sweat affected by heat acclimatization & secretion of aldosterone.
Eccrine Sweat glands
rate of sweat gland secretion only under sym & Ach acting on M3 r.
Activate more glands & increase sweat secretion when preoptic A stimulates intermediolateral cell column in s.c.
Brain & S.C m
sym preganglionic are short & myelinated
post gang are long & unmyelinated
Reverse in parasym (long & myelinated; short & unmyelinated)
Blood Flow
W/ sweat production, BF is under sym control.
Most of skin is non apical
apcial skin of hands, feet, ears, nose & lips diff regulation
Increase in non apical= elevated core temp same sym that control sweat. Instead of vasodilator Ach use VIP or NO & bradykinin. Active vasodilation
Most skin, incrased blood flow will occur in A where evaporative cooling can happen.
Not typical @ rest until more than 25C environment
Blood Flow
Decrease in blood flow, release of NE & NPY vasoconstrictors
Active vasoconstriction
Increase in tone sym, increase in active vasoconstrict while a decrease causes passive vasodilate
Local warming & cooling
Above 35 C doesn’t involve active vasodilation
local vasodilat neuropeptide release by afferent cutaneous sensory neurons
NO locally
Local cooling- activating afferent diff cutaneous sensory neurons to promote NPY & NE release
more pronounced in non apical skin
Apical skin BF
Glomus bodies (arteriovenous anastamose) do not feed cap beds.
From arteriole straight into venules
Under symp control
No local control
Central response
Sweat due to cholinergic sym stimulation
Thermal Reg during reduced ambient temp
core temp decreased when ambient temp decrease
Heat loss red by eliminating all sweating & decrease skin blood flow via sym n. stim (active vasoconstrict)
Heat generated by shivering
Primary motor center for shivering in hypothal- rhythmic oscillating tremors of skeletal m.
Increase metabolic rate of non m. tissues like liver & brown fat. Non shivering thermogenesis. Epi & sym n. stimulation
Longer run- thyroid hormones potentiate sym effects by raising BMR. *imp in infants*
Non shivering thermogenesis
increase BMR but not by activity
Increase in epi, symp & thyorid hormone
Heat as byproduct
Hyperthermia
excercise- body temp rises first
increased heat produced is matched by increased heat loss
set pt for normal temp is unchanged
fever hyperthermia- set point changes first
control center then adj effectors to make actual temp match new set point
Thermal Reg During Exercise
Rise in core temp
Increase sweat & skin BF through sym cholinergic n.
Increase heat transfer
Puts a strain on heart
Dilated skin BV reservoir for blood reducing central BV & cardiac filling
SV decreases, HR increases to maintain normal CO
Body adapts after several weeks w/ reg exercise
Acclimatization
1-8 days, increase in periph heat conductance, higher vasodilate & more Na loss by more sweat rate
Increase in evaportion & temps
After 14 days, lower sweat output & enhanced Na+ reabsorbed. Better sweat distribution & efficient evaporation.
Lower temps
Fever Hyperthermia
Regulated increase in core temp
Response to abnorm elevated temp set pt
Brain interprets this as elevated set pt & starts heat conservation & generation reflex.
Skin BF reduced, shivering stimulated.
Raise body core temp
If in hot environment- vasoconstriction cutaneous
Fever
Pyrogens- release IL or INFs to activate PLA2 to produce PGE2 eventually
PGE2 elevates set pt
Aspirin blocks PGE2 formation
Heat exhaustion
core temp rises above 39 because body cannot dissipate heat load
Dehydration & hypovolemia
Canlead to heat stroke
Heat Stroke
41 C or higher due to impaired thermoreg mech
As body core temp rises, cutaneous vasodilation in excess can lead to fall in arterial P & decrease in brain perfusion.
High temp cause fibronolysis & cosumption of clotting factors so thrombosis & hemorrhage
Rhabdomyolysis of m. & necrosis
Acute hepatic insufficiency, pancreatisis, renal f damage & eliminate electrical activity
Malignant Hyperthermia
rare gen mut of RyR-1 R in skeletal m.
AD manner
Affected exposed to anesthetics which interact w/ R opening Ca2+ channels & produce uncontrolled efflux of Ca2+ from SR
Skeletal m. tetany & large amts of heat production
Core temp can rise dangerously high which leads to skeletal m. death & myoglobin in blood
Give dantrolene- block RyR R
