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PHYSIOLOGY OF
THERMOREGULATION
Conserving and dissipating body heat
Thermoregulation is the ability of
an organism to keep its body
temperature within certain
boundaries, even when the
surrounding temperature is very
different.
Thermoregulation is one aspect of
homeostasis.
A circadian (daily) pattern of
body temperature fluctuation
The integrator.
• The HYPOTHALAMUS of the brain is the
thermostat and integrator (control center) for
temperature.
Homeostasis: Your perception of being hot or cold depends
on the balance between heat production and loss
Factors that produce heat
BMR – basal metabolic rate – the energy
released during minimal physical
activity (at rest).
Factors that produce heat
When cold, your hypothalamus stimulates
muscles to contract – which produces heat.
If that isn’t enough,
small groups of
muscles contract
rhythmically with
even more force
which is shivering!
Factors that produce heat
Physical exercise – Muscle work is
inefficient; a lot of energy is "lost” as heat.
Factors that produce heat
• Hormones – The thyroid hormone is thermogenic. It
increases body heat production.
• DIT (diet-induced thermogenesis) –Heat is produced
during the act of propelling, digesting, absorbing, and
metabolizing food.
Factors that produce heat
Posture – curling up in a
ball reduces your surface
area so there’s less
opportunity for loss of
body heat
Factors that release heat
Posture can also be used to reduce body
temperature. Stretching out increases
surface area having the opposite effect.
Factors that release heat
• Radiation – Loss of body heat by infrared
(IR) heat waves into the environment.
• Conduction – Transfer of heat from the body
to a solid object (like clothing or a cold
bench).
Factors that release heat
• Convection – Warmed air moves away from
the body, replaced with cooler air, cycle
repeats (water also)
• Evaporation – As sweat
evaporates from skin,
it carries the heat away
• Blood vessels also play a direct role in
thermoregulation
• Vasoconstriction: less blood sent to
extremities, keeping core warm
• Vasodilation: more blood enters skin
capillaries for heat loss
• When humidity is high, the sweat glands are
still activated but the sweat can’t evaporate
because the air is already saturated.
• If your body can’t release the heat,
hyperthermia ensues
• This can lead to weakness, dizziness,
cramping, dehydration, and even
stroke
Hypothermia is when your body cannot retain
enough body heat.
This can lead to frostbite and other skin lesions,
limb loss, and brain death
Hypothermia is induced in cardiac
patients & some surgeries to
decrease oxygen needs.
What is brown fat?
Brown fat is thermogenic fat. It is common in
marine mammals.
Infants have several deposits of
brown fat to help them stay warm.
As we age, we lose our brown fat
pads
• Normal adipose tissue (white fat) stores
lipids. Brown fat has more mitochondria
which use the lipids to generate heat.