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B计划的科学 - 紧急避孕

The Science of 'Plan B' - Emergency Contraception

避孕,许多人可以用多种方法避免怀孕
Contraception, with a variety of methods available many people are able to avoid
但如果事情不按计划进行时会发生什么呢?
unintended pregnancies. But what happens when things don’t go quite as planned?
多亏了现代科学,现在有了第二次补救的可能。
Thanks to modern science a second chance is possible. So how does emergency
所以紧急避孕或者计划B是如何生效的呢?实际上女性身体中又发生了什么呢?
contraception or ‘plan-b’ work? And what exactly is happening inside the female
在女性的生理周期期间,大量的荷尔蒙被释放,开启了一个连锁反应。
body? During the female menstrual cycle many hormones are released
脑内垂体释放出FSH(促卵泡激素),
beginning a chain reaction. The pituitary gland in the brain releases FSH
它会刺激小囊和卵巢内卵子的生长。
which stimulates the growth of follicles and a premature egg in the ovaries.
这些小囊释放出雌性激素,
These follicles then release estrogen
帮助子宫内壁做好脱落准备并导致大脑释放
which helps prepare the uterus lining and triggers the brain to release leutinizing
黄体生成素,简称LH。LH会诱使排卵至
hormone or LH. LH then triggers ovulation in which the egg is
卵子会花上十二到二十四小时等待受精的输卵管内。
released into the fallopian tubes where it will spend around twelve to twenty-four
如果卵子没有受精,这段时间内
hours waiting to be fertilized. If the egg isn’t fertilized in this time it
它会开始溶解并在生理期内随子宫内膜一起脱落。
begins to dissolve and is shed away with the uterine lining during menstruation.
虽然这个机会很短暂,但它成功的机率由于
Though this window of opportunity is brief it’s increased by the fact that sperm
精子可以最多存活五天这个事实而增加。
can live for up to five days.
所以几天前的敏锐的精子早早出现,焦虑地等待
So the keen sperm from days ago show up early to the show anxiously awaiting
排卵。
ovulation.
避孕药可以基本调整这些荷尔蒙的分泌水平。
Birth control pills taken on a regular basis modify these hormone levels. By
增高孕酮水平让身体认为自己已经可以
increasing progestin levels the body thinks it’s already released an egg or
怀孕了
already pregnant.
它会有效的减少FSH和LH的排放,并且终止循环。
It effectively decreases FSH and LH and the cycle halts. But in the case
但是这种紧急避孕的方法只在常规避孕手段
of emergency contraception which is only taken if regular contraception methods
失效的情况下
fail,
一些不同的机制才会发生。最重要的是明白
a few different mechanisms take place. The most important thing to understand
受精不是在性交后马上或者几个小时内就会发生
is that fertilization doesn’t happen immediately or even within hours after
实际上是,精子必须要先在输卵管中
intercourse. Instead the sperm must undergo a few biological changes in the
经历一些生理变化。这才是为什么紧急避孕
fallopian tube first which takes time. This is why emergency contraception is
在第二天早上仍然是可行的。
still possible the morning after.
实际上,爱爱后五天内都是有效的。如果在
It can actually work up to five days after intercourse. If taken during the
经期的前半段,紧急避孕
first half of the menstrual cycle, emergency contraception works
可以用来阻止排卵。
specifically to prevent ovulation.
这种方法即便在成熟情况下卵子也不会被释放
This way the egg is not released even though it may be ready and the available
因此精子不能受精
sperm cannot fertilize it.
如果抑制排卵已经太晚
In cases where it’s too late to inhibit ovulation
紧急避孕会增强宫颈粘液稠度来困住精子
emergency contraception is thought to also thicken cervical mucus trapping sperm.
同样的,这会直接抑制精卵结合
As well, it may directly inhibit fertilization between sperm and egg.
临床研究显示,紧急避孕可以在
Clinical studies show that emergency contraception prevents pregnancy
受精前阻止怀孕。没有研究证明紧急避孕
before fertilization. No studies have shown an effect from emergency
可以在受精发生后还有效。它不会
contraception if fertilization has already occurred. It does not stop
阻止受精发生,也不会在受精发生后有任何
implantation from happening nor does it have any effect after implantation has
效果
occurred.
因此,它不会形成堕胎
In this way, its unable to cause an abortion.
并且,尽管这些药物会有些微小的副作用,比如恶心和头痛
And while there are some minor side effects to these drugs, such as nausea and headaches,
科学研究显示所有年龄段的女性
scientific studies have demonstrated its safety in women of all ages and found
服用这种药物的好处也要远大于风险。有什么迫切的问题要我们来解答吗?
that the benefits far outweigh any risks. Got of burning question you want answered?
在评论里或者脸书、推特上找我们吧,订阅我们可以观看我们的每周科学视频
Ask it in the comments or on facebook and twitter, and subscribe for more weekly science videos.

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