The Mircle Of Life- Prenatal Development
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Prenatal Development-The Miracle of Life
Have you ever thought about what an absolute miracle your life is? Imagine how you came to be. Out of thousands of eggs and millions of sperm, one egg and one sperm united to produce you. Had the union of sperm and egg come a day or even a month earlier or later, you might have been every different, maybe the opposite sex or with blonde hair of longer legs. Conception occurs when a single sperm cell from the male unites with an ovum (egg) in the females’ fallopian tube in process call fertilization. The fertilized egg is called a zygote. By the time the zygote ends its three to four day journey through the fallopian tube and reaches that uterus, it has divided into approximately 64 to 128 cells (Eisenberg, Murkoff, & Hathaway, 2002).
The fetus is not immune from the outside world. In fact, some things can be damaging to the unborn child. These are called teratogens, and often result in birth defects. They include such things as maternal disease, poor nutrition, stress, pollutants, and cigarette smoking. Some of the most troubling teratogens are alcohol and drugs. It is critical to the development of the fetus that expectant mothers avoid teratogens, and receive good prenatal care (Baltes, 2003). Other prenatal hazards involve genetic birth defects. A major part in a babys development is directly linked to the actions of the mother takes. To ensure that the baby stays healthy and continues normal development, it may mean to have to make some changes. Pregnant women are encouraged not to use drugs, alcohol, or nicotine as this can seriously affect the babys development. A mother should avoid drinking caffeinated beverages such as coffee and soda while increasing water consumption. Though this all may seem difficult, it is taking an active part in keeping the baby healthy (Baltes, 2003). Exercising is also very important when pregnant. Keeping the baby healthy is just one part of prenatal development but to better understand the full course of prenatal development one must understand physical development during the germinal, embryonic, and fetal period.
The germinal period is the period of prenatal development that takes place in the first two weeks after conception. It includes the creation of the zygote, continued cell division, and the attachment of the zygote to the uterine wall. The differentiation of cells has already commenced, as inner and outer layers of the organism are formed. The blastocyst is the inner layer of cells that develops during the germinal period. These cells later develop into the embryo. The trophoblast is the outer layer of cells that develops during the germinal period. It later provides nutrition and support for the embryo. Implantation, the attachment of the zygote to the uterine wall, takes place about 10 days after conception.
The embryonic period is the period of prenatal development that occurs from two to eight weeks after conception. During the embryonic period, the rate of cell differentiation intensifies, support systems for the cells form, and organs appear. Once the zygote attaches to the uterine wall, the label for the mass of cells changes from zygote to embryo. The embryo consists of three layers of cells: the endoderm, ectoderm, and mesoderm. The endoderm is the inner layer of cells, which will develop into the digestive and respiratory systems. The ectoderm is the outermost layer, which will become the nervous system, sensory receptors (ears, nose, and eyes, for example), and skin parts (hair and nails, for example). The mesoderm is the middle layer, which will become the circulatory system, bones, muscles, and excretory system, and reproductive system. Every body part eventually develops from these three layers. The endoderm primarily produces internal areas, and the ectoderm primarily produces surface parts.
Continuing the embryonic period the embryo’s three layers form, life-support systems for the embryo develop rapidly. These life-support systems include the amnion, the placenta, and the umbilical cord. The amnion is a thin bag or envelope that contains a clear fluid, called amniotic fluid, in which the developing embryo floats. Like the placenta and umbilical cord, the amnion develops from the fertilized egg, not from the mother’s own body. Amniotic fluid helps to cushion and protect the fetus against physical shocks and trauma and provides an environment that is temperature, humidity, and pressure controlled. At approximately 16 weeks, the kidneys of the fetus begin to produce urine. This fetal urine remains the main source of the amniotic fluid until the third trimester, when some of the fluid is excreted from the lungs of the growing fetus. Although the amniotic fluid increases in volume tenfold from the 12th to the 40th week of pregnancy, it is also removed in various ways (Challis & others, 2001). Some is swallowed by the fetus, and some is absorbed through the umbilical cord and the membranes covering the placenta.
The placenta consists of a disk-shaped group of tissues in which small blood vessels from the mother that the offspring intertwine but do not join. The umbilical cord contains two umbilical arteries and one umbilical vein and connects the baby to the placenta. Very small molecules, oxygen, water, salt, food from the mother’s blood, as well as carbon dioxide and digestive wastes from the embryo’s blood, pass back and fourth between the mother and embryo (Bush & others, 2001). Large molecules cannot pass through the placental wall; these include red blood cells and harmful substances, such as most bacteria, maternal wastes, and hormones. The mechanisms that govern the transfer of substances across the placental barrier are complex and still are not entirely understood (Jimenez & others, 2004).
Before most women know they are pregnant some important embryonic developments, such as organogenesis, take place. Organogenesis is the process of organ formation that takes place during the first two months of prenatal development. In the third week, the neural tube forms, this structure eventually will become the brain and spinal cord. At about 21 days, eyes begin to appear, and at 24 days the cells for the heart begin to differentiate. During the fourth week, the first appearance of the urogenital system is apparent, and arm and leg buds emerge. Four chambers of the heart take shape, and blood vessels surface. From the fifth to the eighth week, arms and legs differentiate further; at this time the face starts to form but still is not very recognizable. While organs are being formed, they are especially vulnerable to environmental changes (Wehrens & others, 2004).
The fetal period is the prenatal period of development that begins two months after conception and lasts for about seven months,