Embryonic Stem Cells and Embryology

What are embryonic stem cells?

 derived from embryos that develop from eggs that have been fertilized in vitro 

not

derived from eggs fertilized in a woman's body  typically four or five days old and are a hollow microscopic ball of cells called the blastocyst.

 do not have a specific gene code to be an exact cell  have all of the genes that the other cells do, but their genes are activated for a primary purpose of mitosis without a specialized tissue function  have not undergone differentiation  daughter cells derived from these stem cells are capable of differentiating into almost any kind of cell

 in the laboratory, stem cells can be manipulated to take on characteristics of specific cells, such as heart cells, nerve cells or even pancreatic cells ( a process called directed differentiation).

 during this process, scientists activate certain genes, and deactivate other genes.

 as a result, the newly coded cells develop specific structures to perform certain functions.

Adult Stem Cells

 Stem cells can also come from any body cell  Do not have to be embryonic  Cells are already differentiated

Embryonic Development

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Cleavage :

division of cells in the early embryo Zygotes of many species undergo rapid cell cycles with no significant growth, producing a cluster of cells the same size as the original zygote.   The different cells derived from cleavage are called blastomeres form a compact mass called the morula and Cleavage ends with the formation of the blastula layer of cells) (hollow ball of single

Early Embryological Development Week 1

 Following fertilization , the major events of the first week of development are cleavage , formation of the blastocyst , and the beginning of the implantation process.

 Blastula is formed

Week 2

 By the end of the second week, the blastocyst has completed implantation

Week 3



Gastrulation occurs (bilaminar embryo



trilaminar embryo) - one side of blastula pushes inward - three cell lineages that will eventually form every system ectoderm, mesoderm, and endoderm

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This is the time of early tissue and organ differentiation of the nervous and cardiovascular systems, as well as the formation of future body cavities.

Embryonic Differentiation

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Ectoderm

nervous system, skin 

Mesoderm

muscles, circulatory, skeletal, excretory, and reproductive systems 

Endoderm

linings of digestive and respiratory tracts, liver, pancreas

Week 4

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In week 4, the embryo undergoes major morphological changes as it changes from a trilaminar disk-shaped embryo to a cylindrical embryo.

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This is also an important week in terms of determining placement of future organs.

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Following median and horizontal folding, many organs and body cavities will begin to form or will be repositioned.