時差N小時:頭發(fā)的生長

Whether you have a full head of curly blond hair or anearly bald head with dark hair, the growth of yourhair begins in the skin on your scalp. On the surfaceof your head, the outer layer of cells—called theepidermis—is between ten and twenty layers thick.Some of these epidermal cells actually become haircells by a complex process.

不論你是長著滿頭金發(fā)，還是幾乎謝頂?shù)暮诎l(fā)，頭發(fā)的生長始于頭皮上的皮膚。在頭的表面，有大約10至20層厚的外層細胞——即表皮。實際上其中一些表皮細胞通過復(fù)雜的過程最后變成了毛發(fā)細胞。

To visualize this process, think about taking some plastic kitchen wrap and covering a tub ofcream cheese with it. If you poked your finger into the wrap, and down into the cream cheesewithout breaking the wrap, you would be simulating the beginning of hair development. Inorder for a strand of hair to grow, skin cells must dive down to just below the epidermis. Thiscreates a tube-like structure, much like the one left over if you pulled your finger out of thecream cheese.

為了觀察這個過程，設(shè)想一下：拿些廚房保鮮膜，把它們蓋在一桶奶油奶酪上。如果你用手指戳保鮮膜，在不穿透保鮮膜的條件下碰到奶油奶酪，這就是在模擬頭發(fā)生長初期的情形。為了長出一縷頭發(fā)，細胞必須潛入表皮下面一點。這樣就形成了一種冠狀結(jié)構(gòu)，這種結(jié)構(gòu)與手指抽離奶油奶酪后留下的痕跡一樣。

The cells that line this tubular structure are collectively referred to as the hair follicle. Hairproduction is the result of the cells of the hair follicle depositing layer after layer of proteininto this tubular space. These layers of protein grow out of the tubular space as a strand ofhair.

那些組成這個管狀結(jié)構(gòu)的細胞統(tǒng)稱為毛囊。頭發(fā)的形成就是毛囊細胞向管狀空間注入一層又一層的蛋白質(zhì)的結(jié)果。當這些蛋白質(zhì)層從管狀空間長出后就形成了一縷縷頭發(fā)。

As the hair strand develops, hundreds of pigment-producing cells called melanocytes inject itwith pigment, giving a strand of hair its color. Melanocytes are only able to produce pigmentfor a genetically-determined number of years.

隨著發(fā)絲的生長，成百的黑色素細胞向發(fā)絲注入色素，為頭發(fā)上色。但黑色素細胞只能在遺傳決定的年限內(nèi)生產(chǎn)色素。

Once the melanocytes lose their ability to produce pigment, hair follicles continue to producehair, but instead of brown or red hair, they produce gray hair, which, technically speaking, ishair with no color at all.

一旦黑色素細胞失去生產(chǎn)色素的能力，雖然毛囊繼續(xù)生產(chǎn)頭發(fā)，但不是棕發(fā)或者紅發(fā)，而是白發(fā)。從學術(shù)含義上來講，就是沒有顏色的頭發(fā)。