Development of the Human Zygote
Hundreds of thousands of times a year a single-celled zygote, smaller
than a grain of sand, transforms into an amazingly complex network of cells, a
newborn infant. Through cellular differentiation and growth, this process is
completed with precision time and time again, but very rarely a mistake in the
"blueprint" of growth and development does occur. Following is a description of
how the pathways of this intricate web are followed and the mistakes which
happen when they are not.
The impressive process of differentiation changes a single-cell into a
complicated system of cells as distinct as bold and bone. Although embryonic
development takes approximately nine months, the greatest amount of cellular
differentiation takes place during the first eight weeks of pregnancy. This
period is called embryogenesis.
During the first week after fertilization, which takes place in the
Fallopian tube, the embryo starts to cleave once every twenty-four hours (Fig.
1). Until the eight or sixteen cell stage, the individual cells, or blastomeres,
are thought to have the potential to form any part of the fetus (Leese, Conaghan,
Martin, and Hardy, April 1993). As the blastomeres continue to divide, a solid
ball of cells develops to form the morula (Fig. 1). The accumulation of fluid
inside the morula, transforms it into a hollow sphere called a blastula, which
implants itself into the inner lining of the uterus, the endometrium (Fig. 1).
The inner mass of the blastula will produce the embryo, while the outer layer of
cells will form the trophoblast, which eventually will provide nourishment to
the ovum (Pritchard, MacDonald, and Gant, 1985).
Figure 1:Implantation process and development during
embryogenesis (Pritchard, MacDonald and
Gant, 1985)
During the second week of development, gastrulation, the process by
which the germ layers are formed, begins to occur. The inner cell mass, now
called the embryonic disc, differentiates into a thick plate of ectoderm and an
underlying layer of endoderm. This cellular multiplication in the embryonic
disc marks the beginning of a thickening in the midline that is called the
primitive streak. Cells spread out laterally from the primiti...
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normal infant. When something does go wrong, the embryo or fetus will
unfortunately have some type of defect. The amazing accuracy with which a
single cell can become something as complex as a newborn infant is a truley
incredible feat!
Works Cited
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"Folic Acid for the Prevetion of Recurrent Neural Tube Defect." Medicine March
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Harrison, Ross G. Organization and Develpment of the Embryo. Yale University
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Leese, Conaghan, Martin, and Hardy. "Early Human Embryo Metabolism." Bio
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Pritchard, MacDonald, and Gant. Williams Obstetrics. 17th ed, Prentice-Hall,
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Pritchard, MacDonald, and Gant. Williams Obstetrics, Supplement no. 13. 17th
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"Teratology." ACOG Technical Bulletin February 1985.
Parthenogenesis is a process of generating human embryos from only eggs put therapeutic cloning within reach
Late one night a woman is driving home on the freeway, she’s hit head on by a drunk driver and killed. The man is charged with two accounts of murder; the woman, and her four-week-old embryo inside her. By law, everyone human being is guaranteed rights of life; born or unborn they are equal. The same law should be enforced concerning human embryonic stem cell research. Dr. James A. Thomson discovered stem cells in 1998 and they’ve intrigued scientist ever since. The stem cells themselves are derived from a three to four day old cluster of cells called a blastocyst and they are so coveted because they are pluripotent, meaning they can differentiate into any type of cell in the human body. Although embryonic stem cells show amazing potential to cure various disease such as cancer, congestive heart failure, Alzheimer’s and Parkinson’s disease, muscular dystrophies, and more. The methods by which they are obtained is controversial. Research on embryonic stem cells is unethical, unnecessary, and purely homicide.
Peterson-Iyer, Karen. "Confronting a Fetal Abnormality." http://www.scu.edu. Santa Clara University, Jan. 2008. Web. 13 Mar. 2014. .
but an organ or part of the woman's body, which would make the act of aborting
Sadler, T. W., and Jan Langman. Langman's Medical Embryology. Philadelphia: Lippincott Williams & Wilkins, 2006. Print.
Gender stereotypes have existed since the beginning of modern man. We've all heard them before; male dominance and female weakness, a controlled male and a flustered female, aggression and passion, and many others that all basically boil down to the same thing. Emily Martin, in her essay entitled The Egg and the Sperm, takes this problem of gender stereotype to a new and much more serious level. As an anthropologist, Martin is concerned with the socio-cultural impacts on many different aspects of everyday life, including biology. In doing her research for this article, Martin was trying to uncover suspicions she had about socio-cultural gender stereotypes, and the affects they had on the diction used to describe egg and sperm interactions in numerous biology books and research reports.
"Fetal Development: MedlinePlus Medical Encyclopedia." National Library of Medicine - National Institutes of Health. Web. 06 Mar. 2011. .
"Pregnancy Fetal Development." Stages of Fetal Development. Professional Planets, 1999. Web. 13 Oct 2011. .
The egg is covered with a hard protein shell that called a zona. No sperm is just strong enough to break this shell, so the sperm has to introduce itself properly first. Once the sperm goes through and completes all of the challenges. The egg and sperm take over and begin developing a baby. The development of a baby goes through three trimesters before the parents get to meet their “Life’s Greatest
Baby’s take an average of 38-40 weeks to fully develop and prepare for birth. This time period of approximately nine months is broken down into 3 periods in which the baby spends growing from a tiny mass of cells into a functional, healthy, bouncing baby. If all goes smoothly the birth of a baby, including labor time could take between 4-8 hours, sometimes more, sometimes less. There are many factors that can affect the baby’s growth and development, called teratogens, but overall baby will slowly grow and develop until he or she is prepared to enter into the world.
Every woman when pregnant has a 3-5% chance of having a baby born with a birth defect, and these chances increase when the developing fetus/ embryos are exposed to teratogens, whether it’s intentional or unintentional (Bethesda (MD), 2006). Teratogens can cause severe birth defects, malformations, or terminate the pregnancy altogether (Jancárková, & Gregor, 2000). The placenta is known as an effective barrier from any detrimental pathogen that can potentially hurt the fetus. The timing of exposure of any teratogen is critical to the impact of prenatal development (Bethesda (MD), 2006). The most vulnerable time of the fetus for severe damage is during early pregnancy when all the major organ and central nervous system (CNS) are developing. Miscarriages have an important role in keeping a pregnancy from evolving when there is something serious going on with the developing fetus/embryo. Miscarriages are more common than we think and are the most familiar type of pregnancy loss (Bethesda (MD), 2006).
The first period, the germinal period, is classified as the first two weeks after conception, that is identified by how fast cells divide and differentiate. During this phase a zygote duplicates. After that differentiation begins, this is where early cells take on their own characteristics and move to their predetermined locations. Once that is complete a cell mass will then become either a placenta or a nucleus, together they will become the embryo. The second period is called the embryonic period. This. Is this stage of development that occurs during the third to the eighth week after conception. During this phase, the basic structural forms of the baby's body appear. At the beginning of this period a line (the primitive streak) appears turning into the neural tube, and eventually turning into the central nervous system. in the fourth week eyes, ears, nose, mouth, and minuscule blood vessels (becoming the heart) begin to appear. Between the fifth week and the end of the embryonic period arms, legs, hands, feet, fingers, and toes appear. The final stage, the
Fertilization occurs when the sperm from the male and the ovum from the female combine to create a zygote. The zygote will then go through a gestational period which consists of three different stages. The first stage is the germinal stage and it starts from conception and ends at two weeks, during this stage the zygote divides and becomes much more complex and then implants into the uterine wall where it will then go on to the second stage. The second stage is the embryonic stage, this stage starts at two weeks and ends at eight weeks. During the embryonic stage the zygote has become an embryo and the organs and major body systems form and develop very rapidly. This is one of the most critical periods for physical development, the embryo is very sensitive to many different types of influences. The third and final stage of the gestational period is the fetal stage, this stage starts at eight weeks and ends at birth. During this stage the fetus grows approximately twenty times its previous length and the organs and body systems continue to develop becoming more complex and becomes ready for survival outside of the womb. Children grow the fastest during the first three years of their life, and they will never grow this rapidly again. As the child grows the child will go through various stages of physical development such as puberty and sexual maturity. After the first few
In this report I will be discussing the development issues about prenatal development, and the newborn. Developmental psychology is basically a psychology study that focuses on the cognitive, physical, and social change throughout our life span. In prenatal development we learn about nature and nurture, continuity and stages, and stability and change. Prenatal Development is the process in which babies develop from one single cell after making a baby into an Embryo and later on a fetus . An Embryo is the process of a human organism for about approximately 2 weeks after the fertilization though the second month.
an embryo or of a fetus that is incapable of survival." However, if only the