Like a heating/air conditioning unit in your house, the
regulatory system in charge of your body’s temperature has
sensors (thermoreceptors in skin and hypothalamus), a ther-
mostat (hypothalamus) that sets the temperature, a furnace
(BMR, shivering), and a cooling system (blood flow through
skin, sweat). When you are exposed to the cold (hypother-
mia), the system senses the drop in temperature and re-
sponds by increasing heat production and minimizing heat
loss so that the body temperature increases and returns to
its normal 37°C (Figure 14.18).
N e g a t i v e - f e e d b a c k m e c h a n i s m s t h a t i n c r e a s e h e a t p r o d u c t i o n a n d
d e c r e a s e h e a t l o s s in r e s p o n s e t o d e c r e a s i n g b o d y t e m p e r a t u r e •
F ig u r e 1 4 . 1 8
Effectors
Vasoconstriction
decreases heat
loss through the
skin
Adrenal medullae
release hor-
mones that
increase cellular
metabolism
Skeletal muscles
contract in a
repetitive cycle
called shivering
Thyroid gland
releases thyroid
hormones, which
increase meta-
bolic rate
I
I
I
Increase in body temperature
428 CHAPTER 14
The Digestive System, Nutrition, and Metabolism
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