1. WHAT IS MEAN BODY TEMPERATURE?
• Very different for different animals
WHY?
Regional differences - core body temperature
Hottest region - lumen of stomach +
upper part small intestine - distinctly hotter than
aortic blood
(Grayson, 1983) - not due - digestive or
absorptive functions - nor to metabolism

2. Estimates of body temperature (steady-state conditions)
Tb = (a1 x Tcore) + (a2 x Tskin)
a factors = empirically determined contributions
of core & shell to mean body temperature
Some estimates : 9:1 and 6: 4
Varies with thermal environment and investigator
•Tb = 0.67 Tre + 0.33 Tskin
Which thermal sensors are important?

3. How do you determine mean surface
temperature?
Humans:
Tskin = 0.07Tfeet + 0.32Tlegs + 0.18Tchest + 0.17Tback +
0.14Tarms + 0.05Thand + 0.07Thead
Periphery - skin, mucous surfaces (mouth, nose)
Core - spinal cord, hypothalamus, medulla oblongata, +
Difficult - determine by experiment - which are

4. Chicken - exposed cold Ta -
shivers before change in deep body temperature
Suggests - heat production - controlled by thermal
Kuhnen and Jessen - 1988 - goat
Change - skin temperature - alone -
alters MR

5. 1 Populations of Temperature Sensitive Structures
(skin, spinal cord, hypothalamus)
4. Warm sensors - activity increases with local temperature increase
No discharge at skin temperature below 30 C
Receptors discharge with increase temperature
from 30 >> 35 C
• But little sustained activity
Further increase - skin temperature >> increased sustained
discharge that changes with temperature
Peak activity - 45-47 C
Activity ceases at higher temperature

6. 1. Cold Sensors - activity decreases over same temperature range
Most active at 15 - 35 C & peak at 20 - 30 C
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PARADOXICAL RESPONSE
Most cold receptors >> no discharge above 35 C
But may get discharge near noxious level (43 - 47 C)
(ex. sudden chill - stepping into hot shower)
Also paradoxical warm receptor response - BUT not as common

7. Proportions - cold & warm sensors - vary with site
In general - more warm sensors - hypothalamus
more cold sensors - cutaneous regions
Exceptions - scrotal region - high concentration warm sensors
Sheep & rats - local heating scrotum >> powerful heat
loss effector activity
If sustained >>> decrease in body temperature
Heating scrotum - ram - above 36 C >> panting & decrease
core body temperature (~ 2 C)
Similiar effects - heating mammary skin - ewe

8. General facts about skin temperature
Not homogenous - large difference in skin temperature in
different parts of the body
May account for regional differences by averaging surface area
•BUT - density of skin thermoreceptors are different in
different areas
Larger weight to face and less to extremities
•Face - approx. 20% of total skin signal

9. Skin temperature - represents interaction between
convective heat exchange to surface by
blood + removal of heat (geometry,
external insulation, ambient temperature)
Virtually all skin areas - including trunk -
constrict at cold Ta
(Exception = human forehead -
no vasoconstriction at cold Ta)

10. CENTRAL RECEPTORS
Under normal conditions - trunk sites do not
ary more than 0.5°C
Arterial temperature (e.g., carotid) - contain core
Hypothalamus - contains many neurons and
Preoptic Anterior Hypothalamus (POAH) still a
lack box

11. During heat stress and exercise -
may maintain brain temperature below trunk
In panting carnivores - blood supply passes
through carotid rete
A net-like structure - base of brain
Numerous small arteries embedded in cavernous
sinus
Rete = heat exchanger

12. •Cooled venous blood - evaporating surfaces
(e.g., nasal mucosa)
•arterial blood entering brain
•running antelope - brain temperature ~3°C below
carotid temperature
•Also goat and sheep
•maintenance of lower brain temperature also found in
species without carotid rete (rabbit, squirrel,
monkey, man)
•Nonpanting animals - cool venous blood - sweating
face
Site of exchange with arterial blood - unknown