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 baby’s 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 baby’s 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 embryos 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 mothers 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 mothers blood, as well as carbon dioxide and digestive wastes from the embryos 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, on the average.
Growth and development continue their dramatic course during this time. Three months after conception, the fetus is about three inches long and weighs about one ounce. It has become active, moving its arms and legs, opening and closing its mouth, and moving its head. The face, forehead, eyelids, nose, and chin are distinguishable, as are the upper arms, lower arms, hands, and lower limbs. The genitals can be identified as male or female. By the end of the fourth month, the fetus has grown to six inches in length and weighs 4 to 7ounces. At this time, a growth spurt occurs in the bodys lower parts.
Prenatal reflexes are stronger; arm and leg movements can be felt for the first time by the mother (Lester, 2000). By the end of the fifth month, the fetus is about 12 inches long and weighs close to a pound. Structures of the skin have formed; toenails and fingernails are two examples of this. The fetus is more active, showing a preference for a particular position in the womb. By the end of the sixth month, the fetus is about 14 inches long and already has gained another half pound to a pound. The eyes and eyelids are completely formed and a fine layer of hair covers the head.
A grasping reflex is present and irregular breathing movements occur. By the end of the seventh month, the fetus is about 16 inches long and has gained another pound, now weighing about 3 pounds. During the eighth and ninth months, the fetus grows longer and gains substantial weight, about another 4 pounds. At birth, the average American baby weighs 7? ‘?… pounds and is about 20 inches long. In the last two months, fatty tissues develop, and the functioning of various organ systems step up, for example the heart and kidneys (Lester, 2000).
Now that there is an in depth understanding of the germinal, embryonic, and fetal periods, one can also understand that there is a difference in these three stages and the first, second, and third trimesters of pregnancy. A common way of thinking about issues that arise during pregnancy is in terms of pregnancys trimesters. The trimesters include information about major milestones at the end of each trimester, the mothers physical and emotional changes, feeling the babys first movements, and adjustments in the partners sexual activity.
The first trimester is the first three months, the second is months four through the sixth month, and the third trimester is the seventh month up until birth. An important point is that the first time a fetus has chance of surviving outside of the womb is at about 25 weeks of age. Until recently infants had little chance of surviving outside the womb before the beginning of the third trimester. Because of improved technology and medical advances, younger preterm babies now are surviving. There premies usually need assistance breathing because their lungs are not yet fully developed.
Although these babies often are at risk for medical and developmental problems, their chances of survival have increased dramatically. Today over 90 percent of preterm infants weighing about 2 pounds or more have a more likely chance to survive (BBC News World Edition, 2003). Most pregnancies involve prenatal development that results in a health baby. We have explored the experience of expectant parents during prenatal development and examined ways to maximize the likelihood of having a healthy baby.
For many people, becoming parents is one of the greatest life changes they will experience. Parenthood is permanent, and the physical and emotional nurturing of a child is both a time-intensive responsibility and a wonderful opportunity. This paper discussed the embryo and the fetus. The next step would to be to examine the effects of pregnancy on the expectant parents, also calculating the due date for the pregnancy. Now one has a better understanding of what the miracle of life really is, how it happens and the steps involved in making an infant out of one sperm and one egg.