Monday, November 2, 2009

The Protective Wrapper

When people think about the purpose of skin, most settle on the obvious— the way a few millimeters of tissue keeps their blood from oozing messily out of their body.

While a bit of skin certainly helps hold you together, it also plays several additional roles. First and foremost, its a protective barrier that separates you from the harsh world outside. It helps keep water and nutrients inside your body, where they belong, and it keeps undesirable elements—like toxins and marauding bacteria—outside.

Building a Barrier
To understand how your skin works its defensive mojo, you first need to understand that its actually made up of two distinct layers: the epidermis (which is on the very outside) and the dermis (which is just underneath the epidermis).

The epidermis is your body’s first line of defense. It transforms dead skin cells into a tough, protective layer.

Healthy skin cells start at the bottom of your epidermis, about 1/3 of an inch down, living an easy life and cheerily reproducing. As these cells mature, they get ready to face the outside world by producing a fibrous, waterproof compound called keratin. Keratin is a biological wonder substance. Your body uses it to build your nails and hair, and its the basis of some of the sexier trimmings of other animals, including claws, horns, hooves, scales, shells, and beaks.

When your body produces fresh skin cells, these newcomers push the older cells out of the crowded neighborhood at the base of the epidermis and toward the surface of the skin. The trip takes anywhere from a couple of weeks to a month. By the time a skin cell reaches the surface, its little more than a dead, scale-like structure thats filled with keratin but none of the ordinary cellular machinery. Each surface skin cell lasts about 30 days on the outside, which means you get an entirely new skin every month.

On most of your body, the epidermis is barely thicker than this page. However, the skin on the palms of your hands and the soles of your feet is much thicker, so it can spend all day slapping up against the outside world without wearing off.

Cells are the smallest building block of life. All living creatures—from slimy amoebas to still slimier car salesmen—are made up of cells. Your body contains trillions of cells, many of which don’t belong to you at all. (In fact, the teeny bacteria that digest food in your intestines account for more than half of the cells in your body. Although the process isnt as dramatic, humans shed their skin (and replace it) more often than snakes do. So the next time you act all repulsed by a reptile, perhaps it should really be the other way around.

Shedding Your Skin
Every day, you lose millions of dead skin cells. They don’t fall off all at once—instead, you leave a trail of shed skin everywhere you go. We could tell you how many you lose each minute, but it’s really not that important and likely to make you a little nauseous. (All right, if you insist—30,000 or so scales of skin flake off your body every minute. Right now, on your clothes, on whatever piece of furniture you’re sitting on, and so on. Over the course of a year, you lose about a pound of the stuff.)

You might wonder why you never see much of this skin lying around. That’s because once your skin leaves your body, it’s known by another name: dust. Good estimates suggest that the majority of the material you vacuum off your carpet every week (or every month, or every year) are errant skin flakes. That means that when you clean your house, you’re vacuuming up bits and pieces of yourself and the people who live around you. Yes, there’s some genuine sock lint in there, some cookie crumbs, and a bit of trackedin- from-outside dirt, but it’s mostly skin. Because skin flakes are thin and nearly transparent, your household dust almost always has a light, silverygrey color.

If you want to take a look at your dead skin before it ends up somewhere else, you can try this somewhat unsettling experiment: Stick a piece of clear tape on the back of your hand, strip it off, and then hold it up to a light. You’ll find hundreds of freshly shed skin cells preserved for your inspection.

The Creature That Eats Your Skin
It turns out that your skin flakes have yet another name: lunch. That’s what they are to an unusual family of creatures that exists on a diet made up entirely of dead skin. (And no, they’re not zombies.) The culprits are dust mites— very tiny, distant relatives of the common household spider. Dust mites live in our houses by the millions, with most of them taking up residence in upholstered furniture, drapery, carpets, and— above all—mattresses. Dust mites need just three things for a life of contentment: warmth, moisture, and a steady diet of skin flakes. In your bed, they get all three.

You won’t actually see the dust mites that share your home, because they’re vanishingly small (a family of mites could pack themselves into the period at the end of this sentence). But if you looked at one under a microscope, you’d see an otherworldly, eight-legged creature.

If you’re like most people, dust mites are no big deal and you can safely forget about them. But for some people (estimates suggest one to three people out of 10), dust mites can trigger allergies and even asthma attacks. Common symptoms of dust-mite allergies include sore eyes, an itchy throat, and sneezing fits. If you think you might be allergic to dust mites, it’s worth going to an allergy specialist, who can give you a quick and painless skin-prick test. If you are allergic, you may want to use some of the tips in the box on the next page to help reduce your symptoms.

The problem isn’t the mites themselves—it’s their excrement and (ironically enough) the skin they shed. And here’s more information you probably don’t want to know: Dust mites actually eat and excrete the same skin flake several times, until they’ve finally digested all the goodness out of it.

Before you let the idea of dust mites ruin your day, remind yourself that, unlike some other mites and other nasties, dust mites don’t actually live on your skin— they live in the fabric of the objects around you. In fact, dust mites have absolutely no interest in crawling on your body.

As far as critters you don’t want to think about go, there’s good news, too: Two stubborn skin dwellers that have plagued humankind for generations—the human flea and the body louse—are no longer much to worry about. In Elizabethan times, these creatures crawled into bed with virtually everyone, rich and poor. Today, thanks to relatively simple conveniences like scalding-hot water and laundry machines, these pests (and the unrelenting itchiness they cause) are virtually unknown in the Western world.

Source of Information : Oreilly - Your Body Missing Manual

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