HOW IS A PERSON'S BODY TEMPERATURE REGULATED?
a. Hypothalamus. Human beings, like other mammals, have bodies that stay
about the same temperature even when the outside (environmental) temperature
changes. The body's temperature stays constant because it is constantly monitored by
a small area inside the brain called the hypothalamus (hi-po-THAL-ah-mus). When the
body begins to cool, the hypothalamus causes the body to produce more heat. When
the body becomes too warm, the hypothalamus causes the body to loose heat faster.
These heating and cooling actions are very important since tissue damage and even
death can result if the body gets too cold or too hot. The hypothalamus receives
information concerning the body's temperature from several sources.
(1) Skin. One source of temperature information is the skin. The skin
contains many nerves that have special functions. Some nerves protect the body by
providing information in the form of pain. Other nerves provide the sense of touch. The
hypothalamus uses two other types of nerves. One type senses heat while the other
senses cold. These nerves provide information concerning the temperature of the
(2) Hypothalamus. An important source of information concerning the
body's actual temperature comes from the hypothalamus itself. Part of the
hypothalamus can sense the temperature of the blood flowing through the
hypothalamus. During a hyperthermic emergency such as heatstroke, the
hypothalamus can be overwhelmed and temporarily shut down, causing the body to
lose its ability to cool the body.
b. Cooling Reactions.
(1) Perspiration increases. When perspiration (sweat) on the skin
evaporates, the process uses some of the body's heat. The hypothalamus causes the
body to perspire more. This increased rate of perspiration then results in more body
(2) Blood vessels enlarge. Blood vessels near the surface of the skin loose
heat to the environment. The hypothalamus causes these blood vessels to become
larger (dilate) when the body is too warm. When the blood vessels enlarge, they loose
heat faster. This enlargement causes the skin to have a reddish (flushed) appearance.
c. Warming Reactions.
(1) Muscle activity increases. When the large muscles of the body are
active, heat is produced. When the body becomes too cool, the hypothalamus causes
the large muscles to contract and relax. These contractions and relaxations cycles,
called shivers, produce body heat.