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 ...
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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 ...
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become distinguishable. Most of the substance of the
early embryo will enter into the formation of the head. Blood vessels begin to
develop in the mesoderm and a primitive heart may also be observed (Harrison,
1969). Cells rapidly spread away from the primitive streak to eventually form
the neural groove, which will form a tube to the gut. When the neural folds
develop on either side of the groove, the underlying mesoderm forms segmentally
arranged blocks of mesoderm called somite. These give rise to the dermis of the
skin, most skeletal muscles, and precursors of vertebral bodies. the otocyst,
which later becomes the inner ear, and the lens placodes, which later form the
lenses of ...
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"Development Of The Human Zygote." Essayworld.com. August 10, 2004. Accessed November 22, 2024. http://www.essayworld.com/essays/Development-Of-The-Human-Zygote/12462.
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