Download Biology 1110 Principles of Biology

Biology 1110 Laboratory
Laboratory # 10
Embryology – The Study of the Early
Embryo
Support/Review Materials
All of the micrographs and model pictures in this
presentation were photographed in the MnWest Biology
laboratory unless otherwise noted.
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In this presentation we will study the
development of an animal from the fertilized egg
(zygote) to the embryonic stage known as the
Gastrula.
We take our study to the level of the Gastrula as
to be able to demonstrate the beginnings of
differentiation.
The development that you will see is very similar
to the development of the human embryo.
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When the sperm cell
fertilizes the egg it
delivers half of the
genetic information
required for the new life.
The fertilization also
initiates the early cell
divisions called cleavage
or segmentation
divisions.
Unfertilized Egg or Ovum
Sperm cell
In the fertilized egg the pronuclei of the sperm cell and egg cell
are not visible.
The micrograph on the right contains a fertilized egg and the
embryo that results from the first cell division. Note the
fertilization membrane visible around the 2 cell embryo.
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The micrographs below contain the embyos
that develop during the first few days of life.
This development takes place in the oviduct as
the embryo is traveling towards the uterus.
Eight Cell Stage
Two Cell Stage
Four Cell Stage
Morula
Blastomeres
The cells of the early embryo
are pretty much identical.
These undifferentiated cells of
the early embryo are called
blastomeres.
The four cell stage contains
four balstomeres; the eight
cell stage contains eight
blastomeres.
A morula is a solid cluster of
blastomeres.
A
E
C
D
B
Check your answers on the next slide.
A
E
C
D
B
A – a morula
B – the fertilized egg
C – Two cell stage
D – another morula
E – Eight cell stage
Blastula or Blastocyst
The rapid cleavage of the embryonic
morula cells continues.
Two Blastulas
Through a process called
blastulation the cells begin to
organize themselves around a fluidfilled cavity.
This fluid-filled cavity is called the
blastocoel.
Blastocoel
This process results in the formation
of the blastula or blastocyst as it is
called in mammals.
Blastula or Blastocyst
In the human, the embryo arrives
at the uterus in about 5 days.
During the next few days the
blastula (blastocyst in mammals)
develops.
It is at this stage when the
developing embryo begins the
process of implantation.
Implantation involves the
embryo embedding itself in the
endometrium (lining of the
uterus).
Gastrula
All continued development of the
embryo takes place within the
endometrium.
The process of gastrulation leads to
the formation of the gastrula.
An inner cell mass begins to
develop into the fluid-filled cavity
(the blastocel).
This marks the beginning of the
process of differentiation.
Differentiation
Differentiation is the process
through which relatively
unspecialized cells become
specialized. It is through
differentiation that specific cell and
tissue types develop.
With the development of this inner
cell mass we are seeing the formation
of two of the three embryonic germ
(tissue) layers.
An Early Gastrula
The three embryonic germ are the ectoderm,
endoderm, and the mesoderm. From these germ layers
all other tissues arise.
The developing inner cell mass is the endoderm, the
remaining cells form the ectoderm.
Ectoderm
Endoderm
Gastrula
As the gastrula continues to
develop the endoderm
develops a cavity called the
archenteron.
The archenteron is the
primitive gut. The opening
to the primitive gut is the
blastopore.
Differentiation is well
underway.
Two Late Gastrulas
Archenteron
Ectoderm
Ectoderm
Blastopore
Blastopore
Endoderm
Endoderm
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Ectoderm - the outer body covering; skin and
associated structures, nervous system, sensory
organs such as the eye and ear.
Mesoderm - bone, cartilage, muscle, blood &
blood vessels, lymphatics, kidneys, gonads, &
other. The mesoderm develops a little later
between the endoderm and ectoderm.
Endoderm - epithelial linings of the digestive,
urinary, and respiratory tract, & other.
The fertilized egg (zygote)
Two Cell Stage
A Blastomere
Four Cell Stage
Eight Cell Stage
A Blastomere
A Blastomere
Morula – 16 cell
Later Morula
Blastula - hemisection
Blastula
Blastocoel
Identify the following: ectoderm, endoderm, blastopore,
Archenteron, and blastocoel.
Early Gastrula
Later Gastrula