Embryonic Stem CellsEmbryonic Stem Cellsand and

EmbryologyEmbryology

What are embryonic stem What are embryonic stem

cells?cells? derived from embryos derived from embryos

that develop from eggs that develop from eggs that have been fertilized that have been fertilized in vitro in vitro

notnot derived from eggs derived from eggs fertilized in a woman's fertilized in a woman's body body

typically four or five days typically four or five days old and are a hollow old and are a hollow microscopic ball of cells microscopic ball of cells called the blastocyst. called the blastocyst.

do not have a specific gene code to be an exact do not have a specific gene code to be an exact cellcell

have all of the genes that the other cells do, but have all of the genes that the other cells do, but their genes are activated for a primary purpose of their genes are activated for a primary purpose of mitosis without a specialized tissue function mitosis without a specialized tissue function

have not undergone differentiationhave not undergone differentiation

daughter cells derived from these stem cells are daughter cells derived from these stem cells are capable of differentiating into almost any kind of capable of differentiating into almost any kind of cell cell

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

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

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

Adult Stem CellsAdult Stem Cells

Stem cells can also Stem cells can also come from any body come from any body cellcell

Do not have to be Do not have to be embryonicembryonic

Cells are already Cells are already differentiateddifferentiated

Embryonic DevelopmentEmbryonic Development

CleavageCleavage:: division of cells in the early embryo division of cells in the early embryo

Zygotes of many species undergo rapid cell cycles with no significant Zygotes of many species undergo rapid cell cycles with no significant growth, producing a cluster of cells the same size as the original growth, producing a cluster of cells the same size as the original zygote. zygote.

The different cells derived from cleavage are called The different cells derived from cleavage are called blastomeresblastomeres and and form a compact mass called the form a compact mass called the morulamorula

Cleavage ends with the formation of the Cleavage ends with the formation of the blastulablastula ( (hollow ball of single hollow ball of single layer of cells)layer of cells)

Early Embryological DevelopmentEarly Embryological Development

Week 1Week 1

Following Following fertilizationfertilization, the major events of the first week of , the major events of the first week of development are development are cleavagecleavage, formation of the , formation of the blastocystblastocyst, and , and the beginning of the the beginning of the implantationimplantation process. process.

Blastula is formedBlastula is formed

Week 2Week 2

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

Week 3Week 3

GastrulationGastrulation occurs (bilaminar embryo occurs (bilaminar embryo trilaminar embryo)trilaminar embryo)- one side of blastula pushes inward- one side of blastula pushes inward

- three cell lineages that will eventually form every system - three cell lineages that will eventually form every system ectoderm, mesoderm, and endodermectoderm, mesoderm, and endoderm

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

Embryonic DifferentiationEmbryonic Differentiation EctodermEctoderm

nervous system, skinnervous system, skin

MesodermMesoderm

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

EndodermEndoderm

linings of digestive and linings of digestive and respiratory tracts, liver, respiratory tracts, liver, pancreaspancreas

Week 4Week 4

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

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

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