Friday, September 4, 2009

Fun Fact Friday - You sweat me

Admit it. Living in Florida and owning a yard with gardens, sweat is a way of life. But I love gardening, as evidenced by the chest of my tee shirt from last weekend:

Yes, that's my sweat. It might be gross, but really, when was the last time you saw a sweat stain like this?

Thanks to Chemistry Daily and my unruly lawn and gardens, we all get to learn about perspiration!

Sweating is the loss of a watery fluid, consisting mainly of sodium chloride and urea in solution, that is secreted by the sweat glands in the skin of mammals (like you and me). Sweat also consists of the chemicals or odorants 2-methylphenol and 4-methyphenol.

In humans, sweating is primarily a means of temperature regulation, though it doesn't help all that much in 99% humidity. Evaporation of sweat from the skin surface has a cooling effect due to the latent heat of evaporation of water. Hence, in hot weather, or when the individual feels hot through exercise, more sweat is produced, which explains why I look like I've been in the pool after mowing on an otherwise pleasant Saturday. Sweating is increased not only by physical activity, but also by nervousness and nausea (and in my case, when I drink tequila). Captain Obvious also notes that sweating is decreased by cold. Animals with few sweat glands, such as dogs, accomplish similar results by panting, evaporating water from the moist lining of the oral cavity and pharynx. Most of the time they do this while sitting six inches from your face, and right after they've been licking very personal areas of the personal kind.

In humans, there are two kinds of sweat glands which differ greatly in both the composition of the sweat and its purpose:

Eccrine sweat glands, which are distributed over the entire body surface. These produce sweat that is composed chiefly of water with various salts. These glands are used for body temperature regulation.

Eccrine sweat glands are coiled tubular glands derived from the outer layer of skin but extending into the inner layer. They are distributed over almost the entire surface of the body in humans and many other species, but are lacking in some marine and fur-bearing species. The sweat glands are controlled by sympathetic cholinergic nerves which are controlled by a centre in the hypothalamus. The hypothalamus senses core temperature directly, and also has input from temperature receptors in the skin and modifies the sweat output, along with other thermoregulatory processes.

Human eccrine sweat is composed chiefly of water with various salts and organic compounds in solution. Which explains why I'm so salty. Mmmm, salty!

We also have apocrine sweat glands, that produce sweat that contains fatty materials. These glands are mainly present in the armpits and around the genital area and their activity is the main cause of sweat odor, due to the bacteria that break down the organic compounds in the sweat from these glands. Emotional stress increases the production of sweat from the apocrine glands, or more precisely: the sweat already present in the tubule is squeezed out. Apocrine sweat glands essentially serve as scent glands.

If you're not already wigged out by the whole concept of this, it just gets weirder. In some areas of the body, apocrine sweat glands are modified to produce wholly different secretions, including the wax of the outer ear. Others are greatly enlarged and modified to produce milk.

Thanks for enduring this slightly more personal 'fun fact'. Admit it, you enjoyed it. If not, don't sweat it. There's always next Friday.

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