{"id":159,"date":"2014-09-18T15:39:41","date_gmt":"2014-09-18T15:39:41","guid":{"rendered":"https:\/\/courses.candelalearning.com\/lifespandevelopment1x1\/?post_type=chapter&p=159"},"modified":"2016-03-16T18:19:30","modified_gmt":"2016-03-16T18:19:30","slug":"prenatal-development","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-hccc-ss-152-1\/chapter\/prenatal-development\/","title":{"raw":"Prenatal Development","rendered":"Prenatal Development"},"content":{"raw":"

Periods of Prenatal Development<\/h2>\r\nNow we turn our attention to prenatal development which is divided into three periods: the germinal period, the embryonic period, and the fetal period. Here is an overview of some of the changes that take place during each period.\r\n

The Germinal Period<\/h2>\r\n[caption id=\"attachment_580\" align=\"aligncenter\" width=\"300\"]\"magnified Sperm and Ovum at Conception[\/caption]\r\n\r\nThe germinal period (about 14 days in length) lasts from conception to implantation of the zygote (fertilized egg) in the lining of the uterus.\u00a0During this time, the organism begins cell division and growth. After the fourth doubling, differentiation of the cells begins to occur as well. It's estimated that about 60 percent of natural conceptions fail to implant in the uterus.\u00a0 The rate is higher for in vitro conceptions.\r\n

The Embryonic Period<\/h2>\r\n[caption id=\"attachment_553\" align=\"aligncenter\" width=\"300\"]\"Embryo Photo by Lunar Caustic[\/caption]\r\n\r\nThis period begins once the organism is implanted in the uterine wall. It lasts from the third through the eighth week after conception.\u00a0 During this period, cells continue to differentiate and at 22 days after conception the neural tube forms which will become the brain and spinal\u00a0column.\u00a0Growth during prenatal development occurs in two major directions: from head to tail (cephalocaudal\u00a0development) and from the midline outward (proximodistal\u00a0development).\u00a0This means that those structures nearest the head develop before those nearest the feet and those structures nearest the torso develop before those away from the center of the body (such as hands and fingers). The head develops in the fourth week and the precursor to the heart begins to pulse.\u00a0 In the early stages of the embryonic period, gills and a tail are apparent. But by the end of this stage, they disappear and the organism takes on a more human appearance. \u00a0About 20 percent of organisms fail during the embryonic period, usually due to gross chromosomal abnormalities.\u00a0As in the case of the germinal period, often the mother does not yet know that she is pregnant.\u00a0It is during this stage that the major structures of the body are taking form making the embryonic period the time when the organism is most vulnerable to the greatest amount of damage if exposed to harmful substances.\u00a0(We will look at this in the section on teratology below.)\u00a0Potential mothers are not often aware of the risks they introduce to the developing child during this time.\u00a0The embryo is approximately 1 inch in length and weighs about 4 grams at the end of this period.\u00a0The embryo can move and respond to touch at this time.\r\n

The Fetal Period<\/h2>\r\nFrom the ninth week until birth, the organism is referred to as a fetus. During this stage, the major structures are continuing to develop. By the 12th week, the fetus has all its body parts including external genitalia. In the following weeks, the fetus will develop hair, nails, teeth and the excretory and digestive systems will continue to develop. \u00a0At the end of the 12th\u00a0week, the fetus is about 3 inches long and weighs about 28 grams.\r\n\r\nDuring the 4-6th months, the eyes become more sensitive to light and hearing de, hearing develops. Respiratory system continues to develop. Reflexes such as sucking, swallowing and hiccupping develop during the 5th month. Cycles of sleep and wakefulness are present at that time as well. The first chance of survival outside the womb, known as the\u00a0age of viability\u00a0is reached at about 22 and 26 weeks (Moore &\u00a0Persaud, 1998). Many practitioners hesitate to resuscitation before 24 weeks.\u00a0The majority of the neurons in the brain have developed by 24 weeks although they are still rudimentary and the glial or nurse cells that support neurons continue to grow.\u00a0At 24 weeks the fetus can feel pain (Royal College of Obstetricians and Gynecologists, 1997).\r\n\r\nBetween the 7th and 9th\u00a0months the fetus is primarily preparing for birth. It is exercising its muscles, its lungs begin to expand and contract. It is developing fat layers under the skin.\u00a0The fetus gains about 5 pounds and 7 inches during this last trimester of pregnancy which includes a layer of fat gained during the 8th\u00a0month.\u00a0This layer of fat serves as insulation and helps the baby regulate body temperature after birth.","rendered":"

Periods of Prenatal Development<\/h2>\n

Now we turn our attention to prenatal development which is divided into three periods: the germinal period, the embryonic period, and the fetal period. Here is an overview of some of the changes that take place during each period.<\/p>\n

The Germinal Period<\/h2>\n
\"magnified<\/p>\n

Sperm and Ovum at Conception<\/p>\n<\/div>\n

The germinal period (about 14 days in length) lasts from conception to implantation of the zygote (fertilized egg) in the lining of the uterus.\u00a0During this time, the organism begins cell division and growth. After the fourth doubling, differentiation of the cells begins to occur as well. It’s estimated that about 60 percent of natural conceptions fail to implant in the uterus.\u00a0 The rate is higher for in vitro conceptions.<\/p>\n

The Embryonic Period<\/h2>\n
\"Embryo<\/p>\n

Photo by Lunar Caustic<\/p>\n<\/div>\n

This period begins once the organism is implanted in the uterine wall. It lasts from the third through the eighth week after conception.\u00a0 During this period, cells continue to differentiate and at 22 days after conception the neural tube forms which will become the brain and spinal\u00a0column.\u00a0Growth during prenatal development occurs in two major directions: from head to tail (cephalocaudal\u00a0development) and from the midline outward (proximodistal\u00a0development).\u00a0This means that those structures nearest the head develop before those nearest the feet and those structures nearest the torso develop before those away from the center of the body (such as hands and fingers). The head develops in the fourth week and the precursor to the heart begins to pulse.\u00a0 In the early stages of the embryonic period, gills and a tail are apparent. But by the end of this stage, they disappear and the organism takes on a more human appearance. \u00a0About 20 percent of organisms fail during the embryonic period, usually due to gross chromosomal abnormalities.\u00a0As in the case of the germinal period, often the mother does not yet know that she is pregnant.\u00a0It is during this stage that the major structures of the body are taking form making the embryonic period the time when the organism is most vulnerable to the greatest amount of damage if exposed to harmful substances.\u00a0(We will look at this in the section on teratology below.)\u00a0Potential mothers are not often aware of the risks they introduce to the developing child during this time.\u00a0The embryo is approximately 1 inch in length and weighs about 4 grams at the end of this period.\u00a0The embryo can move and respond to touch at this time.<\/p>\n

The Fetal Period<\/h2>\n

From the ninth week until birth, the organism is referred to as a fetus. During this stage, the major structures are continuing to develop. By the 12th week, the fetus has all its body parts including external genitalia. In the following weeks, the fetus will develop hair, nails, teeth and the excretory and digestive systems will continue to develop. \u00a0At the end of the 12th\u00a0week, the fetus is about 3 inches long and weighs about 28 grams.<\/p>\n

During the 4-6th months, the eyes become more sensitive to light and hearing de, hearing develops. Respiratory system continues to develop. Reflexes such as sucking, swallowing and hiccupping develop during the 5th month. Cycles of sleep and wakefulness are present at that time as well. The first chance of survival outside the womb, known as the\u00a0age of viability\u00a0is reached at about 22 and 26 weeks (Moore &\u00a0Persaud, 1998). Many practitioners hesitate to resuscitation before 24 weeks.\u00a0The majority of the neurons in the brain have developed by 24 weeks although they are still rudimentary and the glial or nurse cells that support neurons continue to grow.\u00a0At 24 weeks the fetus can feel pain (Royal College of Obstetricians and Gynecologists, 1997).<\/p>\n

Between the 7th and 9th\u00a0months the fetus is primarily preparing for birth. It is exercising its muscles, its lungs begin to expand and contract. It is developing fat layers under the skin.\u00a0The fetus gains about 5 pounds and 7 inches during this last trimester of pregnancy which includes a layer of fat gained during the 8th\u00a0month.\u00a0This layer of fat serves as insulation and helps the baby regulate body temperature after birth.<\/p>\n\n\t\t\t

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Candela Citations<\/h3>\n\t\t\t\t\t
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