EFFECTS OF EXPOSURE TO COLD
During exposure to cold, the body
temperature is maintained by two mechanisms.
1. Heat production
2. Prevention of heat loss.
HEAT PRODUCTION
When body is exposed to cold, heat is
produced by the following activities:
1. By Accelerating
Metabolic Activities
Heat gain center in hypothalamus is
stimulated during exposure to cold. It activates the sympathetic centers, which
cause secretion of adrenaline and noradrenaline. These hormones, especially
adrenaline increase heat production by accelerating cellular metabolic
activities.
2. By Shivering
Shivering is the increased involuntary muscular
activity with
slight vibration of the body in response to fear, onset of fever or
exposure to cold. Shivering occurs when the body temperature falls to about 25°C
(77°F).
Primary
motor center for shivering is situated in posterior hypothalamus near the
wall of the III ventricle. During exposure to cold, heat gain center activates
the motor
center
and shivering occurs. Enormous heat is produced during shivering due
to severe muscular activities.
PREVENTION OF HEAT
LOSS
When the body is exposed to cold, heat
gain center in the posterior nucleus of hypothalamus is stimulated. It
activates the sympathetic centers in posterior hypothalamus, resulting in
cutaneous vasoconstriction and decrease in blood flow. Due to decrease
in cutaneous
blood flow, sweat secretion is decreased and heat loss is prevented.
EFFECTS OF EXPOSURE TO SEVERE COLD
Exposure of body to severe cold leads
to death, if quick remedy is not provided. The survival time depends upon
environmental temperature. If a person is exposed to ice cold water, i.e. 0°C for
20 to 30 minutes, the body temperature falls below 25°C (77°F) and the person
can survive if he is placed
immediately in hot water tub with a
temperature of 43°C (110°F). Survival time at 9°C (28°F) is about 1 hour and at
15.5°C (60°F) it is about 5 hours.
Effects of exposure of body to extreme
cold are:
1. Loss of temperature regulating
capacity
2. Frostbite.
LOSS OF TEMPERATURE REGULATING
CAPACITY
Temperature regulating capacity of
hypothalamus is affected when the body temperature decreases to about 34.4°C
(94°F). Hypothalamus totally looses the power of temperature regulation when
body temperature falls below 25°C (77°F). Shivering does not occur. In addition
to loss of hypothalamic function, the metabolic activities are also suppressed.
Sleep
or coma
develops due to depression of central nervous system.
FROSTBITE
Frostbite is the freezing of surface
of the body when it is exposed to cold. It occurs due to sluggishness of
blood flow. Most commonly,
the exposed areas such as
ear lobes and digits of hands and feet are affected. Frostbite is common
in mountaineers. Prolonged exposure will lead to permanent damage of the
cells, followed
by thawing
and gangrene (death and decay of tissues)
formation.
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