Human Development from Conception to Birth

Topics: Pregnancy, Embryo, Uterus Pages: 7 (2498 words) Published: October 19, 2010
There are many reasons that certain drugs damage to an embryo very early in pregnancy even before the mother realizes she is pregnant. Firstly, some of the mother already exposed to certain drugs before she get pregnant such as tobacco and alcohol. For example, the women who take cigarettes everyday in their daily life will continue to smoke before they realize it. Due to this, the babies of mother who smoke tend to grow more slowly in the womb and are likely to be born prematurely and small (Habek et al., 2002). Apart from that, some of the women did not go to consult doctor when they were sick, and just simply take any medicine they have in the house. Especially antibiotics, analgesics, and asthma medications, these kinds of medicines are known as prescription as well as nonprescription drugs, however, may have effects on the embryo or fetus that the women never imagined. Furthermore, many women often consume caffeine by drinking coffee, tea, or colas or by eating chocolate as their daily habits. A review of studies on caffeine consumption during pregnancy concluded that a small increase in the risks for spontaneous abortion and low birth weight occurs for pregnant women consuming more than 150 milligrams of caffeine (approximately two cups of brewed coffee) (Fernandez & others, 1998). Therefore it is too late when the mother realizes they are pregnant, because the drugs already damage the embryo during the germinal period which takes place about 10 to 14 days after the conception. Every human being begins life as a single cell, formed when father's sperm fertilizes mother's egg. Fertilization normally takes place in the mother's Fallopian tube, which connects the uterus (womb) with the ovary. The uterus is the size and shape of a large pear: it is made of muscle and it stretches to allow the baby's growth throughout the months of pregnancy. A woman ordinarily has two tubes and two ovaries, one at each side of her uterus. Every month one of the ovaries in turn releases an egg (ovum) which passes slowly along the tube towards the womb cavity. If the egg is not fertilized within 12 hours or so of being released, it dies; it cannot develop further. But if the woman has sexual intercourse during the days of her monthly cycle just before or at the time when an egg has been released from the ovary, then many sperm cells released by her partner may travel up to the Fallopian tube and one may fertilize the egg. When fertilization is completed and the nuclei of egg and sperm have combined, a new being comes into existence and is capable of further development. Because the parents are human - belonging to the species Homo sapiens - the new being is also human. Fertilization (by which we mean conception) marks the beginning of the human lifespan. The zygote contains the 46 chromosomes that are the genetic blueprint for the individual’s development. It takes about 266 days (about 9 months) for the zygote to become a fetus of billions of cells that is ready to be born. This prenatal development is divided into three stages or periods; the germinal period, the embryonic period, and the fetal period. The germinal period lasts approximately 2 weeks. For the first week or two, the zygote divides many times through mitosis forming the blastocyst, a hollow ball of cells about 150 cells that is the size of the head of a pin. When the blastocyst reaches the uterus around day 6, it implants tendrils from its outer layer into the blood vessels of the uterine wall. This is quite an accomplishment; only about half of all fertilized ova are successfully implanted in the uterus. In addition, not all implanted embryos survive the early phases of prenatal development. Approximately 15% of recognized pregnancies end in miscarriage, and many unrecognized pregnancies – perhaps as many as 50% are believed to terminate with miscarriage. Many of these early losses are because of genetic defects. The embryonic period occurs from the third to the...
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