DC 2007-04-06, In The Womb 子宫日记 3

9' 50-14‘40

1 day - 1 week - 2 weeks

Soon after fertilization, the egg begins its journey, traveling along the fallopian tube toward the safety of the uterus. About a day after fertilization, the egg divides for the first time. Every cell in the body will need its own copy of the genetic blueprint. The chromosomes reproduce first, making an identical copy of the entire genetic code. When the two sets of chromosomes part, the nucleus splits in two and the cell divides.

This process of division continues as the clump of cells travels down the fallopian tube. After four or five days, the tiny ball called the blastocyst has grown to around 100 cells, and it begins to separate into two sets. The outer ring of cells will become the placenta (胎盘) —the life support system—while the inner circle will become the embryo itself.

At this stage, the inner cells are known as stem cells. Stem cells have the remarkable capacity to turn into （=become）any one of over 200 different types of cells, and they can grow to become any part of the body. After seven days, the blastocyst reaches the end of the fallopian tube and arrives in the uterus—a haven for the next nine months.

More than a week has passed since conception, but until she misses a menstrual (月经的) cycle, the mother may not even realize she is pregnant. Over the course of the first trimester or first three months, the single egg will begin to transform itself into a fully formed baby. But all the features of the human body—limbs, nerves, organs, muscles—will be mapped out in the fragile first nine weeks.

The embryo is now starting to take shape. During the third week, the embryonic ball of cells, no bigger than a pinhead, folds in on itself to form a long tube. The top of the tube is growing into the head, and the trunk of the body stretches down below. The head doesn't look much like a head yet. But at day 15, nerve cells begin to form in what will become the brain—as well as in the spinal column, which is exposed and totally unprotected by either skin or bone.

For now, the mother is most likely unaware that her body is creating a protected world—one that can successfully sustain a pregnancy. Yet drastic changes immediately begin to sweep through her system. Her blood volume may increase by up to 50% to cope with the extra demand for oxygen from the parasitic growth in her womb. Once the embryo embeds itself in the uterus, it starts to draw from the mother's bloodstream all that it needs to grow.

words and phrases:

blastocyst : 胚泡

spinal column: 脊柱

parasitic : 寄生的