Lec.2 MECHANISMS IN EMBRYONIC DEVELOPMENT Flashcards
Encompasses all the processes whereby a single cell, the fertilized egg or zygote, gives rise to first an embryo then a fetus.
Intra-uterine development is divided into: embryonic period and fetal period (which consists primarily of growth and organ refinement)
E m b r y o n i c D e v e l o p m e n t
This period is initiated at fertilization.
when the oocyte is penetrated by the fertilizing spermatozoon resulting in the formation of the one-celled zygote.
Here, the maternal pronucleus and the paternal pronucleus fuse and develop. pronucleus = nucleus of the germ cells
-where all major organ systems are established
E m b r y o n i c P e r i o d
*Embryonic period
At the first postfertilization mitosis the zygote develops into the 2-cell embryo.
This, and subsequent early embryonic cells, are referred to as ____.
Cell division of blastomeres do not increase the volume of the cell. This process is called ____
The blastomeres eventually form a small mulberry-like cluster of cells referred to as the ____
Initially, it is characterized by bulging individual blastomeres; later, outer cells will adhere tightly to each other and form a more uniform surface.
The outer cells develop into the ____.
A fluid-filled cavity, the ____, develops inside the trophectoderm.
The inner cells, forming the inner cell mass (ICM), gather at one pole of the embryo.
This structure is now called ____
Blastomeres
Cleavage
morula
trophectoderm / tropoblast
blastocoele
blastocyst
*Embryonic period
The blastocyst expands, hatches from the ____
The ICM forms an internal and external cell layer, referred to as the ____ and ____, respectively.
These two will establish the bilaminar embryonic disc.
The time period from fertilization to completion of blastulation lasts about:
10 - 12 days in ____
14 days in ____
16 days in ____
The bilaminar embryonic disc is then transformed into a ____, through the process of gastrulation.
Gastrulation leads to formation of the three somatic germ layers, ectoderm, mesoderm and endoderm, and formation of the primordial germ cells.
Following gastrulation, the three somatic germ layers further differentiate into various cell types.
They will eventually form the outline of most organ systems.
This marks the end of the embryonic
period.
zona pellucida
hypoblast and epiblast
pigs, sheep, goat & cat
cattle & horses
dogs
trilaminar embryonic disc
The process whereby specialized cell types develop from less specialized cells is known as
In general, before this, there is cell commitment.
gives rise to cells with specialized structure and function, this process alone does not form an organism. this need to be spatially organized in well-defined relationships to each other.
cell differentiation.
reversible phase in cell commitment
cell specification
irreversible phase in cell commitment
cell determination
Within the embryo, cells are often induced to differentiate through cell-to-cell signaling.
Interaction at close range between two or more cells is termed
In order for this to occur, cells to be induced have to be competent or receptive to the inductive signals.
proximate interaction or induction.
manifested through
expression of cell-surface receptors, is
often present only during certain critical
periods.
Competence,
If not induced within this critical period, a competent cell may undergo programmed cell death, called?
is a normal mechanism of embryonic development.
apoptosis,
was the first embryologist to investigate induction.
He observed that when eyes develop, they start as optic vesicles in the mesoderm.
They then bulge outward on each side of the embryo brain.
transplanted the eye mesodermal layer to other parts of the body to see if he could induce lens development in ectodermal layers far removed from the normal eye area.
He found that he could induce lens development practically anywhere on the frog using this method.
Hans Spemann
Upon contact with the overlying ectoderm, the ectoderm invaginates.
It then forms an ____ and, eventually, the lens of the eye.
optic cup
The zygote and the first few generations of
blastomeres have equal developmental
potential, it is called
potency.
Each of these cells is individually able to give rise to all cells, including extraembryonic tissues of the embryo. This cell characteristic is referred to as
totipotency.
Some cells retain their ability to form all tissues of the embryo proper, but lose their competence to form extra-embryonic tissues (placenta). This restricted characteristic is referred to as
pluripotency
