Dogs maintain normal body temperatures around 101.50F.
Smaller dogs may maintain slightly higher temperatures while larger dogs
may maintain slightly lower temperatures (Johnson
1977). The following are methods dogs use to maintain
steady body temperatures:
A dog's primary method of cooling is evaporative cooling from the respiratory
tract through panting. When a dog pants it provides increased air
flow over moist surfaces in the upper respiratory tract through rapid,
shallow breathing. The increase in air flow causes an increase in
evaporation from the upper respiratory tract. Increased ventilation
associated with panting can lead to alkalosis, but this can be counteracted
by a shift to shallow respiration at increased frequency. The increased
ventilation will then be restricted to the upper respiratory tract.
Panting also requires muscular work which produces heat, but dogs use the
elastic properties of the respiratory tract to minimize such heat production.
Due to its elasticity a dog's respiratory tract has a natural frequency
at which it oscillates with little muscular work. At the onset of
panting respiration rate increases rather suddenly from around 30-40 respirations
per minute to around 300-400 respirations per minute. Under a moderate
heat load a dog alternates between brief periods of panting at high frequencies
and periods of normal slow respiration (Schmidt-Nielson
Skin and Fur
A dog's skin is made up of the epidermis and the dermis. The epidermis
is an outer layer of cells that constantly gets replaced. The dermis
is found under the epidermis and supplies it with nerves and blood.
Sweat glands are found in the dermis along with sebaceous glands which
feed oil into hair follicles in the epidermis to lubricate the skin.
Hair grows up through follicles from papillae in the lower epidermis.
More than one hair grows through the same follicle in dogs and one hair
from each follicle, the guard hair, is usually longer than the others.
Dogs can achieve piloerection, raising of the guard hairs, by contracting
or lengthening muscle fibers in the dermis (Whitehead
et al. 1999). A dog's fur insulates it against cold
and heat (Johnson
1977) with the degree of insulation increasing with fur thickness
1997). Dogs normally shed twice a year, in the spring
and in the autumn. Shedding in the spring gets rid of hair that is
not needed for the summer and shedding in the autumn is in preparation
for growing a thicker coat for the winter. Dogs who live indoors
may shed for longer periods of time than those who are kept outdoors because
conditions such as artificial lighting and central heating interfere with
the fur's growth cycle (Whitehead
et al. 1999).
Although dogs have sweat glands, located primarily in the pads of their
feet and in their ear canals, sweating plays a minimal role in their thermoregulation
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