and loss must be balanced in order
to maintain a constant body temperature.
Body extremities tend to be cooler
than the core body temperature, and
that energy is transferred from the
blood to the tissues when blood reaches
Temperature receptors in the skin
detect external temperature.
Temperature receptors in the brain
(hypothalamus) detect the temperature
of the blood.
The brain (hypothalamus) acts as a
processing centre, receiving information
from the temperature receptors, and
triggering the effectors automatically.
Effectors include sweat glands and
At high body temperatures , more sweat
is produced by sweat glands which cools
when it evaporates and blood vessels
supplying the capillaries of the skin
dilate (vasodilation) allowing more
blood to flow through skin capillaries
which increases energy loss.
Heat stroke is an uncontrolled increase
in body temperature.
A common cause of heat stroke is strenuous
exercise when it is warm. Symptoms
include headache, dizziness and an
inability to concentrate. Initial treatment
of heat stroke is to cool the body
e.g. by spraying the skin with water.
Exposure to very hot temperatures
produces increased sweating, and can
produce dehydration, which may lead
to reduced sweating and further increase
of core body temperature.
When core body temperature becomes
too high the normal mechanisms for
controlling body temperature break
At low body temperatures the increased
rate of respiration stimulated when
muscles contract rapidly (shivering)
results in some of the energy transferred
in respiration warming the surrounding
Blood vessels supplying the capillaries
of the skin constrict (vasoconstriction)
restricting blood flow through skin
capillaries which reduces energy loss.
Hypothermia is when core body temperature
falls below 35OC.
Symptoms of hypothermia are drowsiness,
poor coordination and poor judgment.
In hypothermia body heat cannot be replaced
as fast as it is being lost.