Sweating and Water Loss What Is Sweat

Sweat is mostly water with a varying amount of dissolved substances, such as sodium and chloride. In addition, a little potassium, calcium, iron, and other minerals are found in sweat, but the levels of these substances is much lower than sodium and chloride. Sweating is a principal means of getting rid of body heat and keeping the body from overheating. Each liter of sweat can remove 580 calories of heat from the body. Other methods of removing heat from our body include convection, conduction, and radiation (Table 7.1).

Why Do We Sweat?

When "core" body temperature, which is the temperature in and around our vital organs increases, our brain prompts sweating. Sweating is also stimulated by circulating epinephrine, which is released into the blood by our adrenal glands during exercise. This helps us understand why we sweat more when we exercise and why we sweat even more while

Table 7.1 How We Lose Heat from Our Body

Method

Mechanism

Factors

Evaporation Transfer of our body heat to sweat water. This warms the water to its vapor point. Heat leaves body in evaporated water.

Convection Transfer of our body heat into the surrounding air or water (such as swimming in a pool).

Conduction Transfer of our body heat to a object or surface. This could be a chair, bed, bare feet on the floor, etc.)

Radiation Transfer of our body heat to other entities by radiating energy waves. This is similar to the energy waves from the sun warming our body on a sunny day.

Sweating is increased relative to the intensity of exercise and/or as temperature increases.

Convection increases as air or water temperature decreases, and vice versa.

The warmer the objects the less heat that is transferred, and vice

The warmer the objects the less heat that is transferred, and vice exercising in warmer climates. Excessive body heat warms the sweat reaching our skin until the water reaches its vapor point. Sweat water changes from a liquid to a vapor which then lifts off into the air, thus taking heat with it.

Sweating is our principal mean of releasing heat in warmer environments and during exercise.

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