Chordate Embryology
EMBRYOLOGY (from Greek, embryon, "unborn, embryo") Embryology is a science which is
about the development of an embryo from the fertilization of the ovum to the fetus stage.
1
,Before we begin our journey together .
I want to tell you that I was a student one day, and the subject of embryology was pure agony,
and I was tormented by it until the final exam date approached, before I found that magic
solution.
It is watching a 3D video of embryology. This video summarized in a few minutes the suffering
of months of incomprehensible explanation.
Therefore, here is my advice: before you start on any title, you should watch a video of it first
so that things become clear to you when studying.
HISTORY OF EMBRYOLOGY:
Aristotle-Epigenesis (the form of an animal emerges gradually from a
relatively formless egg)
William Harvey(1572-1632)
He was a great believer of the Theory of Epigenesis. He said that there is no part of the
future foetus actually in the egg. but yet all parts are in it potentially Comparative
study of the deer and the chick.
Theory of Preformation (the idea that semen contains an embryo
preformed, miniature infant, or "homunculus" - that simply becomes larger during
development), and the egg just for its nutrition.
Von Baer (1792-1876).( improved microscopy) discovered that embryos took shape in
a series of progressive steps.
After the 1950s, with the DNA helical structure being unraveled and the increasing
knowledge in the field of molecular biology, developmental biology emerged as a field
of study which attempts to correlate the genes with morphological change, and so
tries to determine which genes are responsible for each morphological change that
takes place in an embryo, and how these genes are regulated.
Embryogenesis is the process of cell division and cellular differentiation of the embryo that
occurs during the early stages of development.
The entire process of embryogenesis involves coordinated spatial and temporal changes in
gene expression, cell growth and cellular differentiation .
2
, Steps of Embryogenesis Mechanism of Embryogenesis
Gametes formation Meiotic division
Fertilization. Chemo-attraction
Cleavage Mitotic division
Gastrulation Cell specification, Migration,
Differentiation
Morphogenesis Gene activity, Body axes,
Programmed cell death
nervous Canal
Growth
Cleavage
•The mitotic division of the fertilized egg (zygote) into a number of smaller cells(
Blastomeres)" increasing the number of cells without any increase in size of the initial zygote.
Zygote
Mitotic divisions
An incredible number of cells occupying the same size of the zygote
BLASTULA
3
, Gastrulation
The formation of The Three Germ Layers
Depend on the amount of yolk in the egg
1- Cell Specification
Different regions need to become programmed via particular positions within the fertilized
egg (determinants).
"Determinants or Morphogenetic factors" (Maternal morphogenetic factors), molecules that
direct the differentiation of cells, located in different regions of the egg and become
segregated into different cells during cleavage.
2- Migration
3- Cell differentiation
It's refer to the mechanism whereby different sort of cell arise
Blastula (activation of specific gene) to form 200 different cell type (hepatic cell ,
cardiac cell , …. )
Morphogenesis
Cell and tissue movements Depends on
1- The dynamics of the cytoskeleton
2- The mechanics and viscoelastic properties of cells
The developing organ or organism its shape in three dimensions
4
EMBRYOLOGY (from Greek, embryon, "unborn, embryo") Embryology is a science which is
about the development of an embryo from the fertilization of the ovum to the fetus stage.
1
,Before we begin our journey together .
I want to tell you that I was a student one day, and the subject of embryology was pure agony,
and I was tormented by it until the final exam date approached, before I found that magic
solution.
It is watching a 3D video of embryology. This video summarized in a few minutes the suffering
of months of incomprehensible explanation.
Therefore, here is my advice: before you start on any title, you should watch a video of it first
so that things become clear to you when studying.
HISTORY OF EMBRYOLOGY:
Aristotle-Epigenesis (the form of an animal emerges gradually from a
relatively formless egg)
William Harvey(1572-1632)
He was a great believer of the Theory of Epigenesis. He said that there is no part of the
future foetus actually in the egg. but yet all parts are in it potentially Comparative
study of the deer and the chick.
Theory of Preformation (the idea that semen contains an embryo
preformed, miniature infant, or "homunculus" - that simply becomes larger during
development), and the egg just for its nutrition.
Von Baer (1792-1876).( improved microscopy) discovered that embryos took shape in
a series of progressive steps.
After the 1950s, with the DNA helical structure being unraveled and the increasing
knowledge in the field of molecular biology, developmental biology emerged as a field
of study which attempts to correlate the genes with morphological change, and so
tries to determine which genes are responsible for each morphological change that
takes place in an embryo, and how these genes are regulated.
Embryogenesis is the process of cell division and cellular differentiation of the embryo that
occurs during the early stages of development.
The entire process of embryogenesis involves coordinated spatial and temporal changes in
gene expression, cell growth and cellular differentiation .
2
, Steps of Embryogenesis Mechanism of Embryogenesis
Gametes formation Meiotic division
Fertilization. Chemo-attraction
Cleavage Mitotic division
Gastrulation Cell specification, Migration,
Differentiation
Morphogenesis Gene activity, Body axes,
Programmed cell death
nervous Canal
Growth
Cleavage
•The mitotic division of the fertilized egg (zygote) into a number of smaller cells(
Blastomeres)" increasing the number of cells without any increase in size of the initial zygote.
Zygote
Mitotic divisions
An incredible number of cells occupying the same size of the zygote
BLASTULA
3
, Gastrulation
The formation of The Three Germ Layers
Depend on the amount of yolk in the egg
1- Cell Specification
Different regions need to become programmed via particular positions within the fertilized
egg (determinants).
"Determinants or Morphogenetic factors" (Maternal morphogenetic factors), molecules that
direct the differentiation of cells, located in different regions of the egg and become
segregated into different cells during cleavage.
2- Migration
3- Cell differentiation
It's refer to the mechanism whereby different sort of cell arise
Blastula (activation of specific gene) to form 200 different cell type (hepatic cell ,
cardiac cell , …. )
Morphogenesis
Cell and tissue movements Depends on
1- The dynamics of the cytoskeleton
2- The mechanics and viscoelastic properties of cells
The developing organ or organism its shape in three dimensions
4
