DC 2007-04-09, In The Womb 子宫日记 4

14'55- 21'00

3 weeks - 4 weeks - 6 weeks - 7 weeks

One of the first organs to form is the heart. Until now the tiny clump of heart cells about the size of a poppy seed has been still. But after 22 days a single cell stirs as if jolted to life. This tiny movement sparks (=set off) a chain reaction and other cells in the cluster pick up the rhythm. Incredibly, they all begin to beat in perfect unison. The new cells divide, dance to the same beat and will grow to form the embryo's heart. The muscle cells of the heart are preprogrammed to contract. Later on when the nervous system is more developed, the brain will carefully control the rate of contraction, keeping it steadily beating and pumping for the rest of the child's life.

clump n. A clustered mass; a lump: 块；团：

If she lives to 75 that will be nearly 3 billion heart beats. Without a heart there is no way to deliver the food and oxygen the embryo needs to flourish. Now with the heart pumping, primitive blood cells start to circulate in the fetus through veins no thicker than a hair. The blood cells bring vital supplies of oxygen and nutrients to fuel her phenomenal growth over the next 8 months.

After 4 weeks, the embryo is no bigger than a kidney bean and is growing by about 1/10 of a centimeter everyday. Black dots on her head are the beginnings of eyes. Her miniature single-chambered heart beats 80 times per minute and is getting faster everyday. Emerging buds along her body will grow into arms and legs. Plates of tissue growing in from four sides create her face. The top section grows down to make her forehead and nose. The cheeks fold in from the sides and join to form her top lip. Even in the adulthood, we bear a clear mark from the scene, the vertical groove between the mouth and nose called the philtrum (n.[解]人中). If the sides don't join up properly the baby will develop a cleft palate (兔唇) and may need corrective surgery after she is born.

At day 30, even an expert would find it difficult to tell just from looking at it, if this embryo is going to become a human, a pig, or an ape. Just one and a half percent of our genes make us human. We share 98.5 percent of our DNA with chimpanzees, 3 quarters with dogs, half with fruit flies and a third with daffodils （水仙花）.

For the next few weeks, the embryo will continue to grow according to her own internal genetic blueprint and will become more like a human. The fetus has been growing now for 6 weeks. She is almost an inch long and would fit neatly inside a walnut shell. Just black dots a few days ago, her eyes are now glassy sightless stones with no eyelids set widely apart. Her head is still massive compared to her body. Even at birth, it would be a quarter of her body length. The rest of her body won't catch up with her head until adolescence.