Summer BanksSweat or Perspiration
July 23rd 2006 22:56
Skin
Sweat and glands
The Sweat Gland :
The average person has 2.6 million sweat glands in their skin! Sweat glands are distributed over the entire body -- except for the lips, nipples and external genital organs. The sweat gland is in the layer of skin called the dermis along with other "equipment," such as nerve endings, hair follicles and so on.
Basically, the sweat gland is a long, coiled, hollow tube of cells. The coiled part in the dermis is where sweat is produced, and the long portion is a duct that connects the gland to the opening or pore on the skins's outer surface. Nerve cells from the sympathetic nervous system connect to the sweat glands. There are two types of sweat glands:
Eccrine - the most numerous type that are found all over the body, particularly on the palms of the hands, soles of the feet and forehead
Apocrine - mostly confined to the armpits (axilla) and the anal-genital area. They typically end in hair follicles rather than pores.
The two glands differ in size, the age that they become active and the composition of the sweat that they make. Compared to apocrine glands, eccrine glands:
are smaller
are active from birth (Apocrine glands become active only at puberty)
produce a sweat that is free of proteins and fatty acids.
Cooling Down :
When sweat evaporates from the surface of your skin, it removes excess heat and cools you. This is actually due to a neat principle in physics, which goes like this. To convert water from a liquid to a vapor, it takes a certain amount of heat called the heat of vaporization. This heat energy increases the speed of the water molecules so that they can escape into the air. Typically, all of the sweat does not evaporate, but rather runs off your skin. In addition, not all heat energy produced by the body is lost through sweat. Some is directly radiated from the skin to the air and some is lost through respiratory surfaces of the lungs.
A major factor that influences the rate of evaporation is the relative humidity of the air around you. If the air is humid, then it already has water vapor in it, probably near saturation, and cannot take any more. Therefore, sweat does not evaporate and cool your body as efficiently as when the air is dry.
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