The human body perform countless chemical reactions that are essential for life every second. Many of these reactions can only be performed within a limited temperature range. As a result, humans have a variety of mechanisms to keep their body temperature within a constant range. During exercise, sweating plays an important role in cooling the body by allowing water to evaporate off the skin, resulting in a loss of body heat. Excess sweating can cause dehydration and some electrolyte abnormalities.
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There are two types of sweat glands in humans. The apocrine glands are located primarily in the armpits and genitals. Their function is unclear, but they are thought to represent sweat glands. The eccrine glands, in contrast, are distributed more widely throughout the body and are most concentrated in the palms, soles and armpits. The glands are not present on the parts of the lips, nail beds and parts of the penis and labia. These glands have a coiled structure. Eccrine sweat glands are more important in the maintenance of body temperature.
Activation of Sweat Glands
Sweat glands are supplied by a rich plexus of nerves by the so-called sympathetic nervous system. The sympathetic nervous system controls functions that prepare the body for high-energy activities. These activities include dilating the eyes, increasing the heart rate and blood pressure, decreasing the activity of the digestive tract and breaking down fats to release energy. During exercise, the sympathetic nervous system plays an important role in, among other things, activating the sweat glands to secrete sweat onto the skin.
When the eccrine glands are activated, they secrete sweat. The composition of sweat is similar to the composition of blood, but without blood cells and proteins. The most important constituent is water. Sweat also contains significant amounts of sodium, chloride and potassium. The sweat sits on the surface of the skin and is evaporated by the body heat. As the water is evaporated by heat released from the body, the body cools off. Each gram of water on the body surface absorbs .58 calories of energy before evaporating -- a significant source of heat loss.
Excessive sweating that drips off the skin is, unfortunately, not helpful in temperature regulation. Temperature regulation takes precedence in the body over maintaining hydration. As a result, individuals can sweat excessively during a workout, leading to dehydration. Athletes should consume extra fluids after a workout to compensate for these losses. However, sweat contains more than water -- it also has important salts. Drinking water alone can cause a condition known as hyponatremia, in which the concentration of sodium is decreased. Symptoms of mild hyponatremia include bloating, nausea and vomiting. To compensate for the loss of salt, athletes can drink an electrolyte-replacing energy drink or simply eat some salty snacks after a workout.
- "Textbook of Medical Physiology"; John Hall; 2010
- Kimball's Biology Pages: The Peripheral Nervous System