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At 20 weeks in the womb, humans suddenly sprout tough little casings from the tips of our tiny digits. By the time we're born, our fingers and toes are crowned by fully-formed nails that will be with us for the rest of our lives. Over the ensuing decades, the average person will devote hundreds of hours to carefully clipping, painting and filing these structures. But beyond this dedication to aesthetics, few of us ponder the purpose of our nails.
Why do we have them, and why do they grow?
Nails - Substance - Keratin - Material - Hair
Most of us do know that nails are made of a tough, dead substance called keratin, the same material that makes up hair. But nails actually start out as living cells. Behind the cuticles on fingers and toes, just beneath the skin, a structure called the "root" churns out living cells that go on to form the nail. Also known as the matrix, this little pocket of flesh connects to blood vessels, which supply the nail with the nutrients it needs to make new cells. [Do Hair and Nails Keep Growing After a Person Dies?]
Why Does Alcohol Make You Sleepy ... Then Alert?
Drinks - People - Sleepy - People - Awake
At first, the drinks tend to make people feel super sleepy, but they then jolt those same people wide awake and make them jittery just a few hours later. What's behind this odd effect?
As keratin cells form at the root, they're slowly pushed forward by newly-formed cells jostling for space behind them. Edged out from beneath the skin and into the open, the older cells flatten and harden to form the tough shield of the nail plate. "Continuous division of matrix cells pushes the nail plate forward over the nail bed at a rate of about 3 millimeters [0.1 inches] per month for fingernails, and 1 millimeter [0.04 inches] per...
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