TED科普：为什么有些人会秃顶？
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正常人的头皮上,大概会有10万到15万根头发，可为什么有些人会变成秃顶呢？
实际上我们的毛囊与皮脂腺对于雄性激素是非常敏感的。皮脂腺受到雄性激素的影响就会变得肥大，分泌出大量油脂，就造成了我们常说的“脂溢性脱发”。
一般来说，前额、头顶的毛囊对双氢睾酮的受体活性会比较高，会优先与双氢睾酮结合，然后就优先阵亡了，雄性激素脱发与基因遗传有关，而女性脱发往往是因为压力等后天因素，所以说“娘秃秃一个，爹秃秃一窝”蛮有科学道理。
What do Charles Darwin, Michael Jordan, andYoda have in common?
查尔斯·达尔文、迈克尔·乔丹和尤达有什么共同点？
They, like many other historical andfictive individuals, are bald, in some cases by their own choice.
他们就像许许多多历史人物和 虚构人物一样——都秃顶，有的时候是他们自己选择要秃顶的。
For centuries, a shining dome has been asymbol of intelligence, but despite this, many balding people stillwish their hair would return.
从古至今，闪亮的圆头顶都是智慧的象征，但是尽管如此，很多秃顶的人还是希望他们的头发还能长回来。
Scientists have long pondered, "Why do some people lose their hair,and how can we bring it back?"
科学家们思考良久，“为什么有些人脱发，我们又能怎样再让头发长出来呢？”
The full-headed among us have about 100,000to 150,000 hairs on our scalps, and scientists have discovered two thingsabout this dense thicket.
长满头发的人的头皮上大概有10万到15万根头发，对于这片厚厚的灌木丛，科学家有了两个新发现。
Firstly, the sprouting hair we see ismostly made up of keratin, the protein leftover from dead cells thatare forced upwards as new cells grow beneath them.
首先，我们看到的长出的头发中有很大一部分是由角质组成的，角质就是因为新细胞在它们之下生长而被向上推的死细胞中剩余的蛋白质，
Secondly, the structures that drive hair growth are called hair follicles, a network of complex organs that formsbefore we're born, and grows hair in an everlasting cycle.
其次，使头发生长的结构叫发囊，发囊是复杂器官组成的一个网络，它在我们出生之前就形成了，并且使头发不断生长。
This cycle has three main phases. The first is anagen, the growth phase,
这个周期有3个阶段，第一个阶段是毛发生长初期，即生长阶段。
which up to 90% of your hair follicles areexperiencing right now, causing them to push up hair at a rate ofone centimeter per month.
多达90%的发囊正处于毛发生长初期，使他们以每月1厘米的速度把头发向上推。
Anagen can last for two to seven years, depending on your genes.
根据基因的不同，毛发生长初期可以持续2到7年。
After this productive period, signals within the skin instruct somefollicles to enter a new phase, known as catagen, or the regressing stage,
在这段高产时期之后，皮肤里的信号命令一些发囊进入一个新的阶段，这个阶段叫做毛发生长中期，或者倒退期，
causing hair follicles to shrink to afraction of their original length.
倒退期使发囊缩小至他们原来长度的一小段，
Catagen lasts for about two to three weeks and cuts blood supply to the follicle,creating a club hair, meaning it's ready to be shed.
这个阶段持续2到3周，并且切断毛囊的供血，使其形成一个杵状毛，这意味着头发已经准备好要脱落了。
Finally, hairs enter telogen, the restingphase, which lasts for ten to twelve weeks, and affects about 5-15% of your scalp follicles.
最后，头发进入毛发生长终期，即休止期，休止期持续10至12周，并且影响到你5%到15%的头皮毛囊。
During telogen, up to 200 club hairs can beshed in a day, which is quite normal.
在毛发生长终期，多达200根杵状毛会在一天之内脱落，这是十分正常的。
Then, the growth cycle begins anew. But not all heads are hairy, and, in fact, some of them growincreasingly patchy over time in response to bodily changes.
然后，生长周期又重新开始，但是，不是所有的头都是长满头发的，实际上，随着时间的推移，有些人逐渐长出了斑状，这是对身体变化做出的反应。
95% of baldness in men can be attributed tomale pattern baldness.
男性中95%的脱发是由于男性型秃。
Baldness is inherited, and in people with this condition, follicles become incredibly sensitive tothe effects of dihydrotestosterone, a hormonal product made from testosterone.
秃顶是遗传的，有男性型秃的人，他们的发囊会变得对二氢睾酮异常敏感，二氢睾酮是从睾酮中产生的激素。
DHT causes shrinkage in these overly sensitive follicles, making hair shorter and wispier.
二氢睾酮（DHT）导致这些过于敏感的毛囊缩小，使头发变得又短又细。
But loss isn't sudden. It happens gradually, along a metric knownas the Norwood Scale, which describes the severity of hair loss.
但是脱发不是忽然发生的，它根据一个度量标准逐渐发生，这个度量叫诺伍德分型，它描述脱发的严重程度。
First, hair recedes along the temples, then hair on the crown begins to thin in acircular pattern.
首先，头发沿着太阳穴脱落，然后，头顶上的头发一圈一圈地变稀疏。
At the highest rating on the scale, these balding areas meet and expand dramatically, eventually leaving only a ring of sparsehair around the temples and the back of the head.
在这个分型的最高级，这些秃顶的部分相互连接然后大幅扩张，最后只剩下太阳穴周边一圈稀少的头发，和后脑勺的头发。
Genetics isn't all that drives hair loss.
基因不是导致脱发的唯一原因。
Long periods of stress can release signalsthat shock follicles and force them into the resting phase prematurely.
长期的压力会释放刺激毛囊的信号，并且使他们提早进入休止期。
Some women experience this afterchildbirth. Follicles might also lose the ability to gointo anagen, the growth phase.
一些产后妇女会经历这个阶段。发囊也有可能失去能力，无法进入毛发生长初期，即生长期。
People going through chemotherapy treatmenttemporarily experience this.
接受化疗的人会暂时经历这个阶段。
But while balding may look permanent, scientific investigation has revealed the opposite.
但是，脱发也许看起来是永久性的，科学研究揭示了与其相悖的一面。
Below the skin's surface, the roots that give rise to our hairactually remain alive.
在表皮下，使我们头发生长的发根实际上保持着活性。
Using this knowledge, scientists have developed drugs thatshorten the resting phase, and force follicles into anagen.
运用这个知识，科学家们发明了可以缩短休止期的药物，从而迫使发囊进入毛发生长初期。
Other drugs combat male pattern baldness by blocking the conversion of testosterone to DHT so that it doesn't affect those sensitive follicles.
其他治疗男性型秃顶的药物，通过限制睾酮转变成二氢睾酮的方法来实现，这样，敏感的发囊就不会受到影响。
Stem cells also play a role in regulatingthe growth cycle, and so scientists are investigating whetherthey can manipulate the activity of these cells to encouragefollicles to start producing hair again.
干细胞也起到调整生长周期的作用，所以，科学家们正在研究他们是否可以控制这些细胞的活动，从而促使这些毛囊从新开始长出头发。
And in the meantime, while scientists hone their hair-reviving methods, anyone going bald, or considering baldness, can remember that they're in great company.
同时，当科学家在研究头发再生的方法时，秃顶的者思考秃顶的人，可以记得他们有那些聪明秃顶的人相伴。
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