Thermoregulation Flashcards
Normal body temperature
normal range
- 7 (98.06)
36. 3-37.1 (lowest in the morning, higher as day goes on)
Themoregulation is a FEEDBACK system meaning
information is fed back to the controller to report changes in the controlled variable
Variable maintained around a set point - stable. due to
negative feedback, which brings it back to set point regardless of the direction it changes
FeedFORWARD system
information is used to PREVENT changes in the controlled variable
The vast majority of feedback systems in the human body are
negative feedback
thermoregulation is a _______ system.
feedback, although there are some feedforward aspects
Sensor=
Thermoreceptors
Thermoreceptor definition
thermoreceptors are neurons which change their firing rate in response to changes in local temperature
may be warm or cold sensitive
presumed to be bare nerve endings
Warm Sensitive Thermoreceptors
4 channels identified
TRP-V1-4
sensitive over different ranges
V=vanilloid=capsaicin (hot peppers)
Discharge rate of warm sensitive thermoreceptors
low when temperatures are low (out of range)
increase with increasing temperature
at high enough levels, it decreases again, maybe indicating we are damaging them and compromising function
Cold Sensitive Thermoreceptors
Two receptors TRPM8, TRPA2
also activated by menthol
channels open as temperature decreases
allows Na or Ca influx
discharge rate of cold sensitive receptors
high when temperature is low
decrease as temperature increases
if T gets high enough , you may have a second peak (when something is VERY hot)
Thermoreceptor locations
skin, viscera and brain
different locations tell the brain about different temperatures
Contoller =
hypothalamus
The hypothalamus has the connections to control __________________ that are part of thermoregulation
hormonal, autonomic, and behavioral changes
The part of the hypothalamus that responds to heat
anterior
the anterior hypothalamus
responds to heat
contributes to heat loss behaviors
The part of the thalamus that responds to cooling
posterior
the posterior hypothalamus
responds to cooling
contributes to heat production behaviors
The variable that we want to keep stable over a wide range of environmental temperatures
core temperature
the carter we get from the core,
the more variance we get in body temperatures - these things (hands,feet) are not controlled by the brain, they are just along for the ride
Body T changes with sleep
decreases
circadian influence
set point decrease
Body T changes with exercise
increases (as high as 40)
increased heat production
set point increase
Temperature influenced by circadian rhythm
varies 1-2 degrees over a 24 hour period, lowest in the morning around 6 AM
The ______ has a ______ for core temperature
hypothalamus
set point
Set point=
the desired value
______ determines the set point for core temperature
hypothalamus
Thermoreceptors are found in
brain, skin, gut
Thermoreceptors are found in
brain, skin, gut
Two kinds of information you need to know for thermoregulation
what my current body temp is
what is the temperature around me
Current body temp
T affects enzyme activity (Q10)
will change cellular function
for better or worse, usu worse
Environmental body temp
is a threat to body temp, since I am always generating heat, my problem is usu getting rid of heat
Thermoreceptors in the core - where
brain and viscera
Cutaneous thermoreceptors - where
axons located in the sin
Cutaneous thermoreceptors - what
TELL US ABOUT ENVIRONMENTAL CONDITIONS
often bimodal (T and touch)
may be warm or cold (10X as many cold sensitive)
Visceral thermoreceptors - what
sense core temperature
sense threats to maintenance (food ingested may change body T - tell hypothalamus about these threats) feed forward
Central thermoreceptors - where
preoptic and superoptic regions of hypothalamus
central thermoreceptors - what
neuron cell bodies sensitive to changes in T
3X as many warm sensitive, they relay their information to other areas of the hypothalamus
Detection of CORE temp
preoptic and superoptic regions of hypothalamus and visceral thermoreceptors
detection of ENVIRONMENTAL temp
cutaneous thermoreceptors
Hypothalamus - thermoregulation
integration of afferent
determination of set point
compare set point to core T - if different , generate response (feedback)
respond to environment (feed forward)
Two general categories of effectors
heat loss
heat production
Heat production mechanisms and ways of producing heat
ANS - sympathetic system
Hormonal - thyroxin, epi, norepi
Muscular activity - shivering, jumping up and down
Non shivering thermogenesis (non muscular)
Heat production - muscular activity
Shivering= dorsomedial posterior hypothalamus (increase motorneuron excitation)
increase voluntary activity = cortex (jumping, running)
Heat production - non shivering thermogenesis
Hormonal influence strong = thyroxin increases metabolic rate (heat production), stimulus for TRH release is cold; epinephrine
Increae food intake= increase metabolism
Brown adipose tissue
Heat production - brown adipose tissue
low efficiency hydrolysis of ATP (=lots of heat production)
sympathetic innervation of brown fat, circulating dpi
importance in human = strong in infants, recent evidence shows existence in adults, but located more in white fat (requires exposure to cole and sympathetic activation)
Heat loss - evaporative heat loss (EHL), two kinds
energy (heat) lost as water evaporate
- insensible (respiratory)
- sweating (controlled)
Heat loss - convection and conduction
convection = movement of molecules away from contact (air heating and rising)
conduction= transfer of heat between objects in physical contact with one another
Heat loss - convection and conduction
convection = movement of molecules away from contact (air heating and rising)
conduction= transfer of heat between objects in physical contact with one another
Heat loss - radiation
infrared radiation transferring heat between 2 objects not in physical contact (you and the walls)
Heat loss - can we control these forms (convection, conduction, and radiation) of heat loss
yes, put on a jacket
In order to respond to changes in core temperature, the hypothalamus will
adjust both heat loss and heat production
Integrative responses to increased Core T
Tb> Tsetpoint
decrease heat production (apathy inertia, anorexia)
increase heat loss (blood to skin, EHL - sweat, insensible heat loss - pant)
Heat loss - cutaneous blood
how much blood is sent to the skin determines how much heat moves from blood to external environment
Heat loss - sweating (innervation)
sympathetic CHOLINERGIC innervation
Ach is NT, binding to a muscarinic receptor (anatomically sympathetic) - want to vasodilate so ACH is the NT of choice
Heat loss - sweating (sweat gland)
lots of blood vessels nearby
coiled region by vessels
duct leading to skin
sweat starts out as a filtrate of plasma
Sweating process
plasma and ions (no proteins) are filtered from blood vessel to sweat glands –> primary secretion is high in WATER, Na–> water, Na are reabsorbed (taken back to the blood) in the duct of the sweat gland–>sweat is released to environment
sweating - low flow rate:
concentrated, little water, high Na
sweating - high flow rate:
lots of water, little Na, dilute
Sweating - along the duct reabsorb
Na, Cl and water
aldosterone can help reabsorb the Na
Integrative responses to Decreased Core temp
Tsetpoint> Tb
increase heat production (shivering, non shivering thermogenesis)
decrease heat loss (blood away from skin, decrease evaporative heat loss)
Fever - definition
a controlled increase in body temperature
fever - implication
set point increase: body T is only doing what hypothalamus directs it to do
Making of a fever
Step 1 - the bug (secretion of endotoxins), immune cells (release cytokines) lead to production of PGE2 –> increase hypothalamic set point for T. TBTSETPOINT
Step 5 - increase heat loss, decrease heat production
Step 6 - TB=TSETPOINT, real comfort
Hyper and hypothermia - definition
uncontrolled changes in body temperature
hyper and hypothermia - implications
set point remains normal
environmental stresses exceed body;s ability to regulate temperature
at extremes - hypothalmic regulation may be lost
