When the sweat gland is
stimulated, the cells secrete a fluid that is similar to plasma. It is
mostly water and it has high concentrations of sodium and chloride and
a low concentration of potassium, but without the proteins and fatty acids
that are normally found in this fluid that are normally found in plasma.
The source of this fluid is the spaces between the cells, which get the
fluid from the blood vessels in the dermis. This fluid travels from the
coiled portion up through the straight duct. What happens in the straight
duct depends upon the rate of sweat production.