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Chapter 2: The Facts of Embryology

A Human Embryo is a Human Being

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What is the Early Human Embryo?

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The Third Week: Gastrulation and Neurulation

The point is that...

  • From the moment that the chromosomes of the sperm and oocyte combine, the newly formed embryo can be identified as a distinct, new, and enduring organism.
  • Whether by any of the cloning techniques, the embryo has all of the genetic material needed to grow.

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The embryo not only possesses all necessary organizational information in order to mature, but also has an active disposition to develop itself using that information.

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In the third week, the embryo is sandwiched between two fluid-filled cavities: the amniotic cavity on the top (dorsal cavity) and the yolk sac on the bottom.

1. Distinct from any cell of the mother or father

2. Human

3. A complete or whole organism, though immature

While looking down upon the top of the embryonic disk, we can see that it is shaped like a serving platter- slightly oval.

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The Second Week

what else Could it be?

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What will happen is over the next week, the embryo will elongate (one side becoming the head and the other, the rump)

The embryo develops further

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  • Like spermatozoa?
  • Like ova?
  • A disordered growth?
  • Somatic cells (skin, muscle, etc.)?

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Human Embryo=Human Being

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Introduction

Much of the morphological change concerns the formation of extraembryonic structures, such as the amniotic cavity and amnion, the primary and secondary yolk sacs, and the connecting stalk, and the chorionic stalk

NO! The human embryo, zygote, or fetus can be nothing other than a human being!

However, the embryo develops a third layer through the process of gastrulation. In gastrulation, the three primary germ layers will begin to manifest early neural structures through neurulation.

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The First Week: Cleavage and Implantation

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Gastrulation

Conclusion

Much of the second week after fertilization is still concerned with implantation, which is not completed until day ten to twelve.

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Gastrulation begins with the migration of cells to the center and back of the embryonic disc.

  • Almost every human being's life begins at the end of fertilization.
  • An embryo is a human being, and nothing less.
  • Ending an embryo's life is ending a human being's life.

The newly formed zygote is not yet in the uterus yet. He must make a journey there.

Even though he does not grow in size, he begins his first processes of biological development.

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Stages in the development

Bibliography

George, Robert P., and Christopher Tollefsen. Embryo: A Defense of Human Life. New York: Doubleday, 2008. Print.

Schmidt, Eric. "Google Images." Google Images. Google, 4 Sept. 1998. Web. 05 Sept. 2015.

Implantation makes it possible for the embryo to receive oxygen and nutrition from the mother.

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This is also known as the primitive streak, identifying the front end of the embryo and the right and left sides of the embryo.

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Many cells from the epiblast migrate through the primitive streak and go on to form a new layer of cells: ectodermic cells, endodermic cells, and mesodermic cells.

the primitive streak

The various structures necessary for providing the embryo with a suitable environment and adequate nutrition are in place at such an early time.

In the primitive streak, the cell destination becomes more rigidly determined.

Cell Divisions

If an embryo is produced by either IVF or cloning, is she still a human organism?

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IVF

Because cloned embryos have the same intrinsic potential and fundamental dynamic of development as do other embryos, they ought to be granted the same moral status as other human embryos.

However, prior to the primitive streak, cells are sufficiently uncommitted to specialized roles so that when their processes are disrupted, twinning is possible.

Cloning

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These are also referred to as "cleavages". The resulting cells are smaller and enclosed within the "zona pellucida"

Single, individual human organism who is brought into existence outside of the natural environment she needs to survive. (Page 50)

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Claire Kotwicki, Brooke Burke, Sammie Escamilla, Aidan Gelbach

Dr. Gildersleeve

Beginning of Life 4A

September 25, 2015

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This is why until the primitive streak happens, it is only possible for the embryo as a whole to divide, with each new embryonic whole capable of developing toward the mature stage of a human being.

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Resulting in.......IDENTICAL TWINS!!!

The first cleavage is from one cell to two. The following cleavages are asynchronous (not occurring at the same time). These cells of the embryo are called blastomeres.

By three days after conception, the embryo contains around sixteen cells and look something like a blackberry.

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Sex Cells

At about eight to ten cell stage, the blastomeres undergo a process of "compaction". The blastomeres change their shape and become tightly aligned.

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Embryology tells us otherwise....

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Development of the Embryo Proper

Thus Moore and Persaud wrote, “The initial totipotent cell that is the result of fertilization marked the beginning of each of us as a unique individual.”

  • Not whole, distinct organism
  • Each has only half of what is needed to make a new human
  • Fertilization- only genetic material enters into composition of a new organism

At this stage, the morula has an inner group of cells called the inner cell layer and an outer cell layer.

Dependent on the activity of the Trophoblast

Embryologist: Persuad

The cells of the trophoblast send specific biomolecular signals to the cells of the inner cell mass. This promotes their further development.

Two changes are particularly important.

William Larson wrote, “Male and female sex cells unite at fertilization to initiate the embryonic development of a new individual.”

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embrylogist: william larson

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Ronan O’Rahilly and Fabiola Muller stated that, “A new, genetically distinct human organism is formed when the chromosomes of the male and female pronuclei blend in the ooctye.”

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embryologist: ronan o'rahilly

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The first part, a thin outer layer called the trophoblast, is the progenitor of the placenta.

The whole embryo at this point is referred to as a blastocyst

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The second part, the inner cell mass called the embryoblast, gives rise to the early embryo proper.

neurulation and primitive streak

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Going back to the primitive streak, it extends toward the middle of the embryo until about eighteen days, at which time a different line of cells, the notochord, emerges.

The changes

At four or five days, the morula-stage embryo enters the uterus!

The notochord is crucial to neurulation, the formation of the nervous system.

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This disc gives rise to the germ layers that form all tissues and organs of the embryo

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Bruce Carlson states that, “the notochord...is a cellular rod running along the longitudinal axis of the embryo just ventral to the central nervous system.”

The first change is the division of the inner cell mass into a two-layered embryonic disc (in the third week, a third layer is generated).

The distinction between the inner and outer becomes more pronounced.

A fluid-filled space called the blastocyst cavity seperates the embryo into two parts.

The second change is that in one of the two layers, they hypoblast (the other is the epiblast), the prechordal plate develops which indicates the future cranial region of the embryo and the future site of the mouth. The prechordalplate is also an important organizer of the head region.

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ending of the third week

By the end of the third week, the embryo has gotten himself ready to enter the next four-week phase of intense structural development, the period of morphogenesis.

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By 10 to 12 days after fertilization the embryo is completely embedded in the endometrium. It takes in nourishment from surrounding maternal issues.

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Over the next two days, the zona pellucida degenerates, and the embryo eventually pierces a hole in it, from which he exits the zona membrane.

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This is called hatching. The embryonic human then grows rapidly. Six days after fertilization, the blastocyst attaches to the uterine lining.

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