自然受孕丨医学英语视听学习

Conception

自然受孕

Fertilization is the epic story of a single sperm facing incredible odds to unite with an egg and form a new human life. It is the story of all of us.

受精是精子跨越艰难险阻，与卵子结合，形成新生命的漫长而艰难的过程。这是我们所有人类的故事。

During sexual intercourse, about 300 million sperm enter the vagina. Soon afterward, millions of them will either flow out of the vagina, or die in its acidic environment. However, many survive because of the protective elements provided in the fluid surrounding them. 

性交期间，约3亿精子进入阴道。不久后，数以万计的精子或从阴道流出，或被酸性环境杀死。然而，许多精子在其周围液体内的保护性元素的供给下，得以存活下来。

Next, the sperm must pass through the cervix, an opening into the uterus. Usually it remains tightly closed, but here the cervix is open for a few days while the woman ovulates. The sperm swim through the cervical mucus, which has thinned to a more watery consistency for easier passage.

接着，精子必须通过宫颈。宫颈是通向子宫的开口，它通常保持紧闭状态，但是在女性排卵期，则会张开数日。精子会穿透宫颈粘液，此时宫颈粘液非常稀薄，精子更易于穿透。

Once inside the cervix, the sperm continue swimming toward the uterus, though millions will die trying to make it through the mucus. Some sperm remain behind, caught in the folds of the cervix, but they may later continue the journey as a backup to the first group.

但是在穿透宫颈粘液时，成千上万的精子将被吞噬掉。精子进入宫颈后，继续向子宫游动。一些精子停下来，滞留在宫颈褶皱中，但是它们可能会继续前行，成为第一个“增援组”。

Inside the uterus, muscular uterine contractions assist the sperm on their journey toward the egg. However, resident cells from the woman's immune system, mistaking the sperm for foreign invaders, destroy thousands more.

精子进入子宫内，在子宫肌肉收缩的作用下，向卵子游动。然而，女性免疫系统内的常驻细胞则误将精子作为外来入侵者，摧毁数以千计的精子。

Next, half the sperm head for the empty fallopian tube, while the other half swim toward the tube containing the unfertilized egg. Now, only a few thousand remain.

随后，一半精子向空的输卵管行进，而另一半则游向未受精卵子所在的管。现在，只剩下几千精子。

Inside the fallopian tube, tiny cilia push the egg toward the uterus. To continue, the sperm must surge against this motion to reach the egg. Some sperm get trapped in the cilia and die.

精子进入输卵管内，此时，卵子在细小纤毛的推动下，向子宫移动。精子必须逆着纤毛摆动的方向涌向卵子。一些精子会被困在纤毛中死亡。

During this part of the journey, chemicals in the reproductive tract cause the membranes covering the heads of the sperm to change. As a result, the sperm become hyperactive, swimming harder and faster toward their destination. At long last, the sperm reach the egg. Only a few dozen of the original 300 million sperm remain.

在这段行程中，生殖道内的化学物质促使精子头部覆盖的膜发生变异。因此，精子会变得过分活跃，朝目的地更猛更快地游动。最后，精子终于追上卵子。而最初的3亿精子仅剩下几十个。

The egg is covered with a layer of cells called the corona radiata. The sperm must push through this layer to reach the outer layer of the egg, the zona pellucida.

卵子上覆盖着一层称为“放射冠”的细胞。精子必须穿透这层细胞，才能到达卵子的外层-透明带。

When sperm reach the zona pellucida, they attach to specialized sperm receptors on the surface, which triggers their acrosomes to release digestive enzymes, enabling the sperm to burrow into the layer. Inside the zona pellucida is a narrow, fluid-filled space just outside the egg cell membrane.

当精子到达透明带时，它会与表面的受体结合，从而触发精子顶体释放消化酶，使精子钻入透明带。透明带内部是充满液体的狭窄间隙，位于卵子细胞膜外。

The first sperm to make contact will fertilize the egg. After a perilous journey and against incredible odds, a single sperm attaches to the egg cell membrane. 

第一个钻入透明带的精子将使卵子受精。在经历这段危险，充满磨难的历程后，“冠军”精子会附着在卵子细胞膜上。

Within a few minutes, their outer membranes fuse, and the egg pulls the sperm inside. This event causes changes in the egg membrane that prevent other sperm from attaching to it.

几分钟内，它们的外膜融合，卵子将精子“拉入”其内部。这一事件会导致卵膜发生变化，阻止其他精子进入。

Next, the egg releases chemicals that push other sperm away from the egg and create an impenetrable fertilization membrane. As the reaction spreads outward, the zona pellucida hardens, trapping any sperm unlucky enough to be caught inside. Outside the egg, sperm are no longer able to attach to the zona pellucida. 

接下来，卵子释放化学物质，推开其他精子，并形成一层无法穿透的受精膜。随着反应向外扩散，透明带变硬，进一步阻止正在进入的精子，外面的精子再也无法附着在透明带上。

Meanwhile, inside the egg, the tightly packed male genetic material spreads out. A new membrane forms around the genetic material, creating the male pronucleus. 

与此同时，卵子内部，紧密堆积的男性遗传物质将扩展开。遗传物质周围形成一层新膜，产生雄原核。

Inside, the genetic material reforms into 23 chromosomes. The female genetic material, awakened by the fusion of the sperm with the egg, finishes dividing, resulting in the female pronucleus, which also contains twenty-three chromosomes. 

雄原核内的遗传物质重组成23条染色体。精子和卵子融合后，女性遗传物质被唤醒，完成分裂，形成雌原核，雌原核也包含23条染色体。

As the male and female pronuclei form, spiderweb-like threads, called microtubules, pull them toward each other. The two sets of chromosomes join together, completing the process of fertilization. 

随着雄原核和雌原核形成，蜘蛛网状的微管将它们彼此拉近。两组染色体组合在一起，完成受精过程。

At this moment, a unique genetic code arises, instantly determining gender, hair color, eye color and hundreds of other characteristics.

此时产生的遗传密码是独一无二，它们将决定性别、头发颜色、眼睛颜色，以及其他数百种特征。

This new single cell, the zygote, is the beginning of a new human being. 

精子和卵子结合，形成的新的单细胞受精卵，是新人类发育形成的开端。

And now the cilia in the fallopian tube gently sweep the zygote toward the uterus where he or she will implant in the rich uterine lining, growing and maturing for the next nine months until ready for birth.

现在，输卵管内的纤毛轻轻地将受精卵扫向子宫，受精卵将在富含营养物质的子宫内膜上着床，然后在接下来的9个月内发育成熟，直至出生。