The Physiology of Sweating

Oct. 31, 2009 - PRLog -- It is caused by the stimulation of the anterior hypothalamus-preoptic area in the brain
either by conduction or by excess heat. The hypothalamus contains the thermosensitive
neurons which regulates the heat regulatory function of the body though inputs from the
temperature receptors in the skin.
Physical heat and emotional stress are two situations wherein the nerves will stimulate sweat
glands to produce sweat. Emotionally induced sweating is generally restricted to palms, soles,
and forehead, while physical heat produces sweating throughout the body.
Through sweating, the body regulates its temperature. High skin temperature reduces the
hypothalamic set point for sweating and through a negative feedback mechanism, core
temperature decreases setting the process of sweating.
When a person transfers from a cold to a hot climate, adaptive changes occur in the
mechanism of sweating. The process of acclimatization increases the maximum rate of
sweating and decreases its solute composition.
The secretory portion of the sweat gland produces a precursor secretion which is an active
secretory product of the epithelial cells lining the coiled portion of the sweat gland. It is the
cholinergic sympathetic nerve fibers ending on or near the glandular cells that produces the
secretion. The precursor secretion is similar to the composition of plasma, without the plasma
proteins. Sodium concentration is 142 mEq/L and chloride concentration is 104 mEq/L. Most
of the electrolytes, the sodium and chloride, flows through the ductal portion of the sweat
gland to be reabsorbed. The rate of reabsorption is dependent on the rate and degree of
sweating.
When the sweat glands are only stimulated lightly, the precursor fluid flows through the
duct slowly hence, almost all the essential sodium and chloride ions are reabsorbed and
becomes concentrated. This results to a decrease in the osmotic pressure of the sweat fluid
consequently reducing the reabsorbed water. Thus, at low rates of sweating, urea, lactate
and potassium are usually very concentrated.
On the other hand, when the sweat glands are strongly stimulated by the sympathetic
nervous system such as during exercise, large amounts of precursor secretion are formed. As a
consequence, the ions are reabsorbed only slightly resulting to a dilute sweat, to a maximum
of 50 to 60 mEq/L. Also, the sweat flows rapidly through the glandular tubes that little are
reabsorbed.
Any moisture on the skin will evaporate unless if it is a humid environment wherein
evaporation causes cooling as dictated by the laws of physics. Sweat provides an additional
cooling effect since there is more water available for evaporation. However, some
evaporation is inevitable in body tissues, termed as “insensible perspirationation” due to the
moist body tissues.
The production of sweat varies from one individual to another. Genetics may play a role on
the production of excessive sweat. The type of activity of an individual, the emotional factor
and medical problem of a person dictates the amount of sweat that will be produced.
However, sweating may also be a manifestation of a more serious illness. If sweating is
accompanied by fever, weight loss, chest pain, shortness of breath and rapid, pounding of
the heart, it is wise to visit a doctor to check if there is something more serious that what you
expect.

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