Download 3.5 EMBRYOLOGY notes 2014

Development of Animal Cells
Aka…Embryology
Embryology
- study of the development of an embryo
5 major stages…
1. Gametogenesis - gamete production
 2. Fertilization - gamete --> zygote
 3. Cleavage - Zygote --> Blastula
 4. Gastrulation - Blastula --> Gastrula
 5. Organogenesis - Organ Formation


-i.e. Neurulation- Gastrula --> Neurula
Fertilization:
male and female gametes fuse to form a zygote

Funnel shaped end of
a Fallopian Tube is the
usual site for
fertilization

A sperm must penetrate
the egg


Now it is called a
ZYGOTE
Tiny cilia line the tube to
propel the fertilized egg
toward the uterus
Cleavage
(Process by which a zygote divides by mitosis to form 2 new cells)

Cell # doubles with
each division
(two cells will divide to
form ___ cells and so
on)
 each cell smaller than
zygote

MORULA:
a zygote consisting of about 12-32 cells in a
solid ball
 Reaches the uterus in about 3-4 days after
fertilization

BLASTOCYST formation
Cells start to compact and move
to the edge of the cell, leaving
a fluid-filled space in the
center- this will eventually form
the Blastocyst (also called
blastula for other animals)

a.
b.
c.
a hollow ball of cells that forms
btwn 5-8 days after fertilization
This will attach to the lining of the uterus
cell division continues
Cells on 1 side of the blastocyst begin to
fold inward to form the gastrula
Blastocyst structure

Three parts:


Blastocoel- fluid filled empty
space
Inner Cell Mass- embryonic stem
cells


No longer OMNIPOTENT cells.
Now they are PLURIPOTENT (can
become anything except the
placenta)
Trophectoderm- outer layer of
cells

Provides nutrients to the developing
embryo and will eventually form the
placenta
Gastrulation
Blastula (hollow ball of cells) transformed into the Gastrula (three-layered stage)
Gastrulation - sorts all the cells into distinct cell
layers (ectoderm, endoderm, and mesoderm)
Gastrulation forms 3 distinct tissue layers

Layer on the outer surface
of the gastrula is called the
ECTODERM

eventually forms the
SKIN and NERVOUS
tissue
ENDODERM

Layer on the INNER
SURFACE of the gastrula is
called the ENDODERM

ENDODERM eventually
develops into the lining of the
digestive tract and organs
associated with digestion
MESODERM

Mesoderm is the 3rd cell
layer found in the
developing embryo
between the ECTO and
ENDODERM (“meso”
means middle)

MESODERM Continues to
grow and divide and
eventually develops into
muscle cells, circulatory, and
excretory cells, bone cells
and respiratory system