The Thermometer

1
The Thermometer

• 1592 -- Galileo produces the first thermometer
• Early instruments contained water, then wine, and
  finally, in 1670, mercury.
• 1614 -- Italian physician, Sanctorio Santorius,
  published results of studies in which he used his
  own clinical thermometer to determine body
  temperature.
• He concludes that mans temperature remains
  remarkably constant, except during illness, when
  it rises.

2
The Thermometer

• 1714 -- German physicist, Gabriel Fahrenheit,
  constructs a mercury thermometer but chooses a
  rather arbitrary reference point for zero and the
  boiling point of water.
• Zero was the lowest temperature observed in his
  hometown during a particular winter. This was
  not the air temperature, but the temperature of a
  mixture of snow and sal ammoniac!
• The boiling point of water was set at 212o
  (Why???)
• Measured body temperature and found it to be
  constant at 96o.
• At about the same time, a Swedish astronomer,
  Anders Celsius, constructed a thermometer
  choosing the freezing point of water as 0o and
  the boiling point as 100o.

3
The Thermometer

• Whatever the scale, the thermometer provided the
  means of measuring temperature of the air as well
  as of the living body.
• Where to place the instrument, on, or in, the
  body was still to be resolved.
• At first, investigators pressed it against the
  skin, or in the armpit, or between the thighs.
• 1774 -- Dr. George Fordyce first suggests that
  the bulb of the thermometer be placed under the
  tongue.
• 1778 -- John Hunter, and English surgeon and
  anatomist, using relatively small thermometers
  inserted them everywhere
• In humans in the male urethra and the rectum, and
  
• In experimental animals in the body cavities and
  a variety of organs.
• Hunter reported that humans and animals could
  generate heat as well as dissipate heat.

4
The Thermometer

• 1775 -- Charles Blagden, a Scottish physician,
  published the results of his work that contains
  the origins of much of our knowledge of the
  physiology of temperature regulation.
• For example, in an atmosphere of high
  temperature, The external circulation was
  greatly increased the veins had become very
  large, and a universal redness had diffused
  itself over the body.
• it appears beyond all doubt, that the living
  powers were very much assisted by the
  perspiration, that cooling evaporation is a
  further provision of nature for enabling animals
  to support great heats.
• Perhaps no experiments hitherto made furnish
  more remarkable instances of the cooling effect
  of evaporation than these last facts a power
  which appears to be much greater than hath
  commonly been suspected.

5
The Thermometer

• Using the thermometer, the abilities of the body
  to generate heat in a cold environment, and to
  dissipate heat when the ambient temperature rises
  were revealed.

Temperature regulation is a fundamental
homeostatic process.
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Poikilothermic vs. Homeothermic Vertebrates

• Poikilotherms (cold-blooded)
• Body temperature fluctuates over a considerable
  range with changing environmental temperature.
• Behavioral temperature regulation.
• Reptiles, amphibia, and fish

• Homeotherms (warm-blooded)
• Body temperature regulated within a narrow range
  in spite of wide variations in environmental
  temperature.
• Temperature Regulatory System(s)

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Temperature Regulatory System(s)
What does the system regulate?

• Core temperature
• varies little with changes in environmental
  temperature.

• Total body heat content is not regulated.
• In general, the body surface and extremities are
  cooler than the core.
• The magnitude of the differences between the body
  surface and extremities and the core varies
  with environmental temperature.

Temperature regulatory systems act to maintain
the core temperature at, or near, a set point.
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• Variations in Core Temperature
• Normal Range Rectal 97-1000 F (36.1 - 37.8 OC)
• Different organs within the core may differ in
  temperature
• Organ-specific metabolic activity
• Temperature of perfusing blood
• Temperature gradient to surrounding tissues
• e.g., liver gt rectum
• Diurnal Rhythm
• Regular daily fluctuation of 0.90 - 1.300 F (0.5
  - 0.70 C)
• On normal LD and activity
• Lowest approximately 6-7 AM
• Highest approximately 5-7 PM

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Variations in Core Temperature

• Monthly Rhythm in females
• Associated with ovulation
• Progesterone-induced increase (0.5 - 0.60 C or 10
  F) in body temperature
• Maintained during the luteal phase of the
  menstrual cycle.
• During Exercise
• Body temperature rises
• Elevation of body temperature set point.
• Heat produced exceeds heat dissipation.
• Rectal Temperature may rise as high as 1040 F
  (400 C)
• Rise in body temperature is limited by
  thermoregulatory systems which increase heat
  dissipation.

11
Heavy exercise
Core temperature (ºC)
Moderate exercise
Mild exercise
Time (min)
Begin exercise
Fig. 27-16, pg 840
12
Temperature Regulatory System(s)
Variations in Core Temperature

• During Fever
• Increase in the set point for body core
  temperature induced by
• Pyrogens
• Hypothalamic lesions

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• Pyrogens
• Released from toxic bacteria or from degenerating
  body tissues.
• Some pyrogens act directly and immediately on the
  hypothalamic termperature regulating center to
  increase the set point for body core temperature.
• Other pyrogens (e.g., endotoxins from
  gram-negative bacteria) function indirectly and
  may require several hours to cause effects.
• Bacteria or breakdown products are phagocytized
  by leukocytes, tissue macrophages, and large
  granular killer lymphocytes.
• These cells digest the bacterial products and
  then release interleukin-1 (IL-1) and
  interleukin-6 (IL-6)
• IL-1 and IL-6, acting at the hypothalamus,
  stimulate the production of PGE2, that acts to
  elicit fever.

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Antigens recognized as foreign - infectious -
autoimmune - neoplastic
Activated immune response cells - leukocytes -
mesangial cells - vascular endothelial cells -
astrocytes
Production of interleukins 1 and 6
Increased prostaglandin E2 synthesis in the
hypothalamus
Elevation of hypothalamic temperature set point
Increased heat production, reduced heat loss
- vasoconstriction - shivering - behavior
Elevation of hypothalamic temperature to a new
set point fever
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Acting at
16
Fever cessation decreases hypothalamic temperature
set point
Fever increases hypothalamic temperature set point
Heat gain increased and heat loss reduced 1. Skin
vasoconstriction 2. shivering
Core temperature (ºC)
Heat Loss increased 1. Skin vasodilation 2.
sweating
Days
Fig. 27-15, pg 837
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Temperature Regulatory System(s)
Variations in Core Temperature

• Hypothalamic lesions
• Brain surgery in region of the hypothalamus may
  alter the hypothalamic temperature set point
  and induce fever (sometimes hypothermia)
• Compression due to brain tumor may do the same.

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Temperature Regulatory System(s)

• The Crisis or Flush
• If the factor that elevated the set point is
  removed, then the set point returns to normal.
• Patient reports feeling hot.

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Energy Balance,Energy Expenditure, and Total
Heat Production
20
Energy Balance
Energy Expenditure
The energy expended on work done on the external
environment averages no more than about 1 of
the total energy expenditure of the body
21
Physical Laws Governing Heat Exchange between
Living Organisms and the Environment
Evaporation to air
Radiation
Convection to air
Evaporation to air
Conduction to seat
Conduction to handle bar
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CONDUCTION

• Heat exchange between objects or substances
  that are in contact with each other.
• Heat transferred from one molecule to another
  (solids, liquids, gases)

• The rate of heat transfer (D watts/m2) is
  proportional to the temperature difference (i.e.,
  thermal gradient)

D k(T1 - T2)
k conductance thermal conductivity
divided by length of conducting pathway and
multiplied by area of contact T1, T2
temperatures of warm and cool surfaces

• Air is a poor conductor
• Not much heat is lost or gained by body contact
  unless the bare skin is in contact with a good
  conductor

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CONVECTION

• Movement of molecules away from the area of
  contact
• Aids conduction in liquids and gases
• Liquid or gas in contact with surface of
  different temperature is heated or cooled by
  conduction, altering its specific gravity.

• The rate of heat transfer (C watts/m2) is
  proportional to the velocity of the air (V
  m/sec.), as well as, the temperature difference
  between skin and air (Ts - Ta)

• Heat loss by convection increases when cooler air
  replaces air that has been warmed during contact
  with the skin.
• When wind, fans, or movement of the body through
  the air increases the velocity of air (forced
  convection), the rate of heat loss can be
  increased dramatically.

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THERMAL RADIATION

• Exchange of thermal energy between objects in
  space through a process that depends only on the
  absolute temperature and the nature of the
  radiating surfaces.
• Energy will pass from a hot object to a cooler
  one.
• Does not require an intervening medium.
• Speed of light transmission
• Electromagnetic waves from an emitting object
  carry heat away to an absorbing object.
• Electromagnetic waves absorbed by the absorbing
  object are converted to heat.

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THERMAL RADIATION

• The net transfer of heat is the difference
  between the radiation emitted by a surface and
  that which it receives.

In the equation above, the surface quality or
emissivity (e) of a surface is an important
factor.
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Thermal Radiation

• An object with an emissivity (e) 1
• An ideal absorber of radiant energy (i.e., a
  black body)
• Such an hypothetical surface absorbs all incident
  radiation on one side and reflects nothing (e.g.,
  an open window).
• An ideal absorber of radiant energy is also an
  ideal emitter of radiant energy.
• An ideal absorber of thermal radiation (i.e., an
  ideal thermal black body) is also an ideal
  emitter of thermal radiant energy.
• Emissivity (e) 0
• A perfect reflector of radiant energy
• Such an hypothetical surface reflects all
  incident radiation and absorbs none (e.g., highly
  polished metallic surfaces).

Many surfaces are almost black body
absorber/radiators for some wavelengths of
radiation (with es close to 1) , but reflect
other wavelengths quite well (with es close to
0) .
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Thermal Radiation

• Human Skin Colors
• The emissivity (e) of skin varies with the
  wavelength of the radiant energy.
• In the visible spectrum, skin colors vary due to
  differences in the absorbance and reflectance
  (i.e., variations in emissivity coefficient (e))
  for light of various wavelengths.
• All human skin, regardless of color, is an
  excellent absorber/radiator in the infrared
  wavelengths (e is close to 1) .
• For thermal radiation, human skin is a black
  body absorber/radiator
• All skin is black to infrared radiation!

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Rate of heat transfer by thermal radiation to and
from the body
Human Skin 97 perfect infrared black body
absorber/radiator

• The temperatures of surfaces in the environment
  are usually lower than body temperature.
• Surfaces in the environment are highly absorbing
  for infrared radiation
• The equation above assumes that all surfaces are
  black (e1 e2 1)
• If the mean skin temperature (TS) and the
  environmental temperature are not very different
  (i.e., within 200C), then the equation above can
  be simplified

• For a man dressed in shorts and sitting quietly
  in an environment at 250C, R equals about 50 - 70
  of the heat lost from the body (about 30 W/m2).

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Radiation
Heat transfer by radiation to and from the body

• Not all of the body surface is effective in
  radiation exchange with the environment.
• Between the legs, under the arms, and between
  fingers, radiant heat lost from one area is
  absorbed by the opposite skin surface and no net
  loss occurs to the environment.

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Vaporization

• Heat of Vaporization
• Vaporization of 1.0g H2O removes 0.58 kcal.

• The total rate of heat transferred away from the
  body by vaporization (E) is proportional to the
  rate of evaporative moisture lost via two
  different routes
• Insensible evaporation (Ein)
• Not subject to physiological control.
• Sweat evaporation (Esw)
• Some aspects under physiological control
• Other aspects depend on environmental factors.

Rate of heat loss by vaporization E Ein
Esw
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E Ein Esw
Vaporization

• Insensible Evaporation (Ein)

• Ein is not controlled in the regulation of body
  temperature.
• Ein occurs at all times, even in a cold
  environment
• Two components of Ein
• Evaporation of water after its transudation
  through the skin (not sweat).
• Evaporation of water from the respiratory tract.

• At 30 0C,
• Ein 12-15 ml/m2/h X 0.58 kcal/ml 6.96 -
  8.70 kcal/m2/h
• Transudation of H2O through the skin (50 of
  Ein)
• Evaporative H2O loss from the respiratory tract
  (50 of Ein)
• 20-25 of total heat loss

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E Ein Esw
Vaporization

• Sweat Evaporation (Ein)

Esw he (Pws - faPWa)Aw/Ap
33

• Sweat Evaporation (Ein)

Esw he (Pws - faPWa)Aw/Ap
34

• At 30 0C
• Evaporative heat loss is fairly constant (12 -15
  g/m2/h)
• Approximately 25 of total heat loss.
• 50 of evaporative heat loss due to Ein
• 50 of evaporative heat loss due to Esw
• Remaining 75 of heat loss is by other means

• Above 30 0C
• Evaporative heat loss increases linearly with
  increased ambient temperature.

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Rectal Temperature
Skin Temperature
Vaporization
Heat Loss
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Physical Laws Governing Heat Exchange between
Living Organisms and the Environment

• N.B. When the environmental temperature is
  equal to or above the skin temperature, then
• No heat is lost by conduction, convection, or
  radiation because the thermal gradient is zero or
  positive.
• All heat must be lost by evaporation

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• At all environmental temperatures, heat is lost
  by evaporation (Ein Esw).
• If the environmental temperature is less than
  body temperature, then R, C, and D are negative
  quantities (i.e., heat is lost by these
  mechanisms).
• If the environmental temperature is equal to or
  greater than body temperature, then R, C, and D
  are positive (i.e., heat is gained by these
  mechanisms) heat may be lost only by evaporation
  (E).

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Patterns of Heat Loss from the Body during
Different Environmental Conditions and Levels of
Physical Activity
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Temperature Regulation
Patterns of Heat Loss
SKIN TEMPERATURE AND HEAT LOSS

• Transfer of heat from the body to the environment
  via conduction, convection, and radiation depends
  on the temperature gradient between skin and the
  environment.

• Transfer of heat from the body to the environment
  via vaporization depends on the difference in
  saturated water vapor pressures at skin and air
  temperatures.

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SKIN TEMPERATURE AND HEAT LOSS

• If a favorable temperature gradient exists, then
  increasing the skin temperature will increase
  this gradient and increase the rate of heat loss
  via conduction, convection and radiation.

• As relative humidity increases and the value of
  the product faPwa approaches Pws, then
  evaporative cooling becomes less effective.
• At higher skin temperatures, the amount of water
  vapor that can be held in air in contact with the
  skin (indicated by increased Pws) is greater.
  Thus the vapor pressure gradient (Pws - faPWa)
  may also be increased, increasing the efficiency
  of sweat evaporation.

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E Ein he (Pws - faPWa)Aw/Ap
Esw he (35.66 mmHg - 0.517.535 mmHg)
Aw/Ap Esw he (26.89 mmHg) Aw/Ap
Positive value indicates a favorable water vapor
pressure gradient between the skin and the
ambient air.
Water vapor pressure gradient less favorable than
in Scenario 1
Raising skin temperature increases the water
vapor pressure gradient.
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Mechanisms by which Homeotherms increase Heat
Dissipation

• Increased skin temperature
• Improves the rate of heat loss to the environment
  by

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How can body core temperature be kept constant in
a warm environment?
Mechanisms by which Homeotherms increase Heat
Dissipation
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Mechanisms by which Homeotherms increase Heat
Dissipation
Control of Skin Temperature

• Blood Flow
• Arterial blood leaving the core is identical to
  body core temperature (370 C).
• Tissues receiving a high blood perfusion rate
  have temperatures close to the core temperature.
• Also true for skin
• Because the skin is in contact with the
  environment, changing the blood flow to the skin
  also changes the temperature of the skin.
• By changing the temperature of the skin, the
  temperature gradient between the body surface and
  the environment can be altered.
• Via conduction, convection, radiation, and
  vaporization.

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Mechanisms by which Homeotherms increase Heat
Dissipation

• Mechanism by which skin temperature is increased
• Vasodilation of skin vessels
• A reflexive decrease in sympathetic discharge
  occurs in response to an increase in the
  temperature of blood perfusing the
  temperature-regulating center in the hypothalamus
  and/or stimulation of cutaneous temperature
  (warmth) receptors.
• Opening of arterio-venous anastomoses in skin
  while venous flow through the venae comitantes
  (deep veins) decreases.
• Arterial blood perfuses superficial skin veins
  (flushing).
• Warm arterial blood perfuses the skin of the
  extremities.
• Increased conduction and convection of heat from
  core to skin
• Increased skin temperature
• Increased heat dissipation by convection,
  radiation, and evaporation (Esw Ein)

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Fig. 27-6, pg 831
47
Role of the cutaneous circulation in
thermoregulation
Direct effect of increased temp. on resistance
vessels
Decreased sympathetic adrenergic outflow to
resistance vessels
Vasodilation
Increased sympathetic cholinergic outflow to
sweat glands
Increased local bradykinin
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Vasomotor responses to changes in ambient
temperature are greatest in the extremities.
37ºC
37ºC
37ºC
Core
Core
32ºC
Shell
28ºC
34ºC
31ºC
Cold
Warm
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Mechanisms by which Homeotherms increase Heat
Dissipation

• Increased Vaporization
• Increased insensible water loss
• Increased transudation of water through the skin
  due to increased cutaneous blood flow and skin
  temperature.
• Increased sweating

2.5 X 106 sweat glands in humans

• Reflexive increase in sympathetic discharge to
  the sweat glands via cholinergic post-ganglionic
  sympathetic neurons.

• Occurs in response to
• An increase in the temperature of blood perfusing
  the temperature-regulating center in the
  hypothalamus.
• An increase in the temperature of cutaneous
  (skin) temperature (warmth) receptors
• Some segmental reflex control by spinal centers
• (e.g., quadriplegics)

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Epidermis
Excretory duct
Absorption, mainly Na and Cl- ions
Secretory duct
Dermis
Secretion, mainly protein free filtrate
Sympathetic Cholinergic Post-Ganglionic Nerve
Sweat gland
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Mechanisms by which Homeotherms increase Heat
Dissipation

• Increased Vaporization
• Increased insensible water loss
• Increased sweating

Esw he (Pws - faPWa)Aw/Ap
N.B.

• The relative amount of heat dissipated by
  sweating depends on
• Skin Temperature
• Area of wet skin/body surface area
• Environmental temperature
• When the body temperature is equal to or lower
  than the environmental temperature, heat can only
  be lost by evaporation (i.e., heat loss by
  conduction, convection, and radiation is zero or
  negative)
• Relative humidity
• If Esw must be maintained despite increasing
  humidity, then skin temperature and/or the area
  of wet skin must be increased.
• Air movement
• The value of he (water vaporization heat transfer
  coefficient) depends on air movement

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Mechanisms by which Homeotherms increase Heat
Dissipation

• Panting
• In animals with no sweat glands (e.g., dogs)
• Rapid, shallow breathing
• Increases water vaporization from the mouth and
  respiratory passages
• Air moved primarily in respiratory dead spaces
• Relatively little change in the composition of
  alveolar air
• Behavioral Mechanisms
• Alter posture to expose more body surface area
• Remove clothing
• Move to area of lower environmental temperature
• Increase air movement (e.g., fan)
• Lower the environmental temperature (e.g., air
  conditioning)

53
How can body core temperature be kept constant in
a cold environment?
Mechanisms by which Homeotherms decrease Heat
Dissipation
Mechanisms by which Homeotherms increase Heat
Production
54
Mechanisms by which Homeotherms decrease Heat
Dissipation
Control of Skin Temperature

• Decrease skin temperature
• Vasoconstriction of skin vessels
• A direct effect of cold on vasculature
  (transient).
• A reflexive increase in sympathetic discharge
  occurs in response to
• a fall in the temperature of blood perfusing the
  temperature-regulating center in the
  hypothalamus, and/or
• stimulation of cutaneous (cold) receptors.
• Closure of arterio-venous anastomoses in skin and
  shunting of venous blood to venae comitantes

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Mechanisms by which Homeotherms decrease Heat
Dissipation

• Decrease skin temperature
• Vasoconstriction of skin vessels results in

• Decreased conduction and convection of heat from
  core to skin
• Decreased skin temperature
• Decreased heat dissipation by conduction,
  convection, radiation, and evaporation
• Tips of the extremities remain cold, but core
  body heat is conserved.

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37ºC
37ºC
37ºC
Core
Core
32ºC
Shell
28ºC
34ºC
31ºC
Cold
Warm
Fig. 27-5, pg 831
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Mechanisms by which Homeotherms decrease Heat
Dissipation

• Piloerection
• Contraction of microscopic bundles of smooth
  muscle cells attached at one end to hair
  follicles and at the other end to the surface of
  the basal layer of the epidermis.
• Reflexive increase in sympathetic discharge in
  response to
• a fall in the temperature of blood perfusing the
  temperature-regulating center in the hypothalamus
  and/or
• stimulation of cutaneous (cold) receptors.
• Entraps an insulating layer of air next to the
  skin.
• Decreases the convective loss of heat from skin
  to air.

Humans have a paucity of hair which limits the
effectiveness of piloerection.
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Mechanisms by which Homeotherms decrease Heat
Dissipation

• Abolition of Sweating
• Cooling of the temperature-regulating center in
  the hypothalamus below 36.8 0C (98.2 0F)
  completely abolishes sweating.
• Remember Heat loss by insensible evaporation
  (Ein) continues.

• Behavioral Mechanisms
• Postural changes
• Decrease surface area
• Addition of clothing
• Take shelter from air movement
• Increase environmental temperature
• Move to an area of higher temperature

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Mechanisms by which Homeotherms increase Heat
Production

• As the environmental temperature is lowered, the
  body heat losses by conduction, convection, and
  radiation become progressively greater.
• Periphery becomes cooler
• Mean body temperature may fall despite
• Maximal vasoconstriction
• Maximal piloerection
• Altered behavior

• If body core temperature is to be preserved in
  the face of an increase in the rate of heat
  loss,then heat production must be increased.

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Mechanisms by which Homeotherms increase Heat
Production

• Increased muscle contractile activity
• Increased muscle tension
• Stimulation of cold receptors in the skin and
  spinal cord results in
• Reflexive activation of the primary motor center
  for shivering in the posterior hypothalamus.
• Prior to the onset of shivering, there occurs
• an increased sensitivity of muscle spindle
  stretch reflex
• an increased tone of skeletal muscle, and
• increased heat production from skeletal muscle
• When muscle tone exceeds a critical level, then
  shivering begins due to a
• feedback oscillation of the stretch reflex
  mechanism.

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Mechanisms by which Homeotherms increase Heat
Production

• Increased muscle contractile activity
• Exercise
• Increases body heat production
• Increased body temperature

• Shivering and/or Exercise
• The resulting increased body temperature
  increases the difference between the body and the
  environmental temperatures.
• The rate of heat loss by conduction, convection,
  radiation, and vaporization is increased
  (compared to the rate if muscle activity did not
  occur).

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Rectal Temperature
Skin Temperature
Vaporization
Heat Loss
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Mechanisms by which Homeotherms increase Heat
Production

• Endocrine Mechanisms
• Adrenal Medulla
• Epinephrine
• Chemical Thermogenesis
• Immediate, but short duration, increase in
  faculative or non-shivering thermogenesis
• 10-15 increase in heat production in adults as
  much as 100 in infants.
• Brown Fat (uncouple oxidative phosphorylation)
• Increased rate of catabolism of body fuels
• Thyroid Gland
• Thyroid hormones (T4 and T3)
• Slow onset (weeks), but more prolonged, increase
  in metabolism and body heat production.
• Increased set point for thyroid hormone
  feedback with increased circulating T4 and T3.
• In addition, T4 and T3 potentiate effects of
  catecholamines.

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Mechanisms by which Homeotherms increase Heat
Production

• Endocrine Mechanisms
• Adrenal Medulla
• Epinephrine
• Thyroid Gland
• Thyroid hormones (T4 and T3)

• Acclimation to Cold
• Requires several weeks
• Thyroid hormones, epinephrine, and other hormones
  interact to increase body heat production.

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Mechanisms by which Homeotherms increase Heat
Production

• Change in Composition of the Diet
• Thermic Effect of Food (TEF)
• Chemical energy is converted to heat during
  digestion and assimilation of food.
• protein gt carbohydrate or fat

• Increase food intake
• Consume a diet high in protein

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Mechanisms by which Homeotherms decrease Heat
Dissipation

• Decrease skin temperature
• Vasoconstriction of skin vessels close venous
  anastomoses
• Return venous blood in venae commitantes
  counter-current cooling of blood perfusing the
  skin

• Piloerection

• Abolition of Sweating

• Behavioral Mechanisms

Mechanisms which increase Heat Production

• Increased muscle contractile activity
• Increased muscle tension
• Shivering
• Exercise

• Endocrine Mechanisms
• Adrenal Medulla
• Epinephrine
• Thyroid Gland
• Thyroid hormones (T4 and T3)

• Increase food intake
• Change in Composition of the Diet

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Neural Regulation of Body Temperature
69

• Body temperature is regulated almost entirely
  by nervous feedback control mechanisms.
• Temperature-sensitive neurons are found in the
  following locations
• Hypothalamus (warmth and cold receptors),
• Anterior hypothalamus
• Hypothalamic preoptic area
• Monitor temperature of blood perfusing these
  areas
• Midbrain and spinal cord (warmth and cold
  receptors),
• Abdominal viscera (warmth receptors only),
• Skin (warmth and cold receptors).
• Posterior Hypothalamic Temperature-Regulating
  Center
• Integrates sensory information from
  temperature-sensitive neurons.
• Generates efferent signals for controlling
• Rate of heat loss
• Rate of heat production

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Neural Regulation of Body Temperature

• Importance of the Sympathetic Nervous System
• Required for the control of the following
• Sweat gland secretion
• Control of blood vessel diameter
• Epinephrine secretion
• Piloerection

Sympathectomy
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Central Temperature Receptors
Hypothalamic Temperature
Panting Vasodilation Sweating
Experimantal Warming of Hypothalamus
Increased HEAT LOSS
Shivering Vasoconstriction
Experimental Cooling of the Hypothalamus
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Interaction of Inputs from Central and Peripheral
Receptors

• Threshold Core Temperatures for Sweating and
  Shivering
• Sweating
• There is a core temperature (36.8 0C) below which
  no sweating will occur regardless of skin
  temperature.

• Shivering
• There is a core temperature (37.10C) above which
  no shivering will occur regardless of skin
  temperature.

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