Transcript Exercise 44 Embryonic Development

Exercise 44
Survey of Embryonic
Development
Objectives:
Fertilization, zygote, morula,
blastocyst, gastrula, fetus, chorion,
chorionic villi, placenta, amnion,
yolk sac, umbilical cord
 Embryonic structures and
functions

Fertilization

Fusion of two haploid (1n)
gametes, occurs in uterine
tube usually within a day after
ovulation

Sperm
• Delivers paternal chromosomes
to fertilization site

Egg
• Provides all the cellular
organelles, nourishment, genetic
programming for development
AND maternal chromosomes
• ~2000x the volume of the sperm
cell
• Secondary oocyte has been
suspended in Metaphase II until
now
Fig. 29-1
Zygote
Product of fertilization (union of
gametes)
 Contains 46 chromosomes (normal # for
a somatic cell)

Fig. 29-1
Prenatal Development
**Atlas Diagrams

1st trimester
Embryological & early fetal development
 Beginnings of organ systems appear


2nd trimester
 Organs and
 3rd trimester
systems nearly complete
Rapid fetal growth
 Most organ systems functional

Embryonic Development:
MORULA




Day 3-4 of development/cleavage (cell divisions)
Solid multicellular (> 4-cell stage) ball
Morula = “mulberry”
Reaches uterus on day 4
Fig. 29-2
Embryonic Development:
BLASTOCYST





Over next 2 days
Hollow ball with inner cavity
Outer cellular layer (“trophoblast”, provides nutrients)
Inner layer of cells (clustered at one end, will form the
embryo)
Implants in uterine wall
Fig. 29-2
Embryonic Development:
GASTRULA




Day 12
Third layer forms—cells on surface migrate to
central line: “primitive streak”
Migrating cells move between the 2 layers
Now have 3 embryonic layers:
Ectoderm
 Mesoderm
 Endoderm

Fig. 29-4
Embryonic Germ Layers
Neural tissue
Ectoderm
Connective tissues
Epithelia
&
glands
Mesoderm
Muscle tissue
Endoderm
Fig. 29-4
Embryo to Fetus

Fetus:

Start of month 3 to
delivery
Fig. 29-5
Extra-embryonic membranes

Yolk sac


Amnion


Ectoderm & mesoderm
Allantois


Endoderm & mesoderm
Endoderm & mesoderm
Chorion

Mesoderm & trophoblast
Yolk sac



Endoderm + mesoderm
Pouch
Important site of blood
cell formation
Fig. 29-5
Amnion



Ectoderm + mesodermal cells
form this two layered structure
Enlarges throughout
development
Amniotic cavity contains
amniotic fluid

Surrounds, cushions
developing embryo/fetus
Fig. 29-5
Chorion



Mesoderm and trophoblast cells form this vascular
layer
Provides transport of nutrients to the growing
embryo/fetus (multicellular now, so diffusion alone
won’t suffice)
Chorionic villi: branches in contact with maternal
tissues
 Embryonic blood vessels in each
 Supplies embryonic heart (beating by week 3)
 Gases and nutrients diffuse between embryonic
and maternal circulations—no mixing of actual
blood (separated by trophoblast)
Chorion
Fig. 29-6
Placenta




Appearance of blood vessels in
the chorion = 1st step in
creation of a functional placenta
Temporary structure in uterine
wall that allows the diffusion
between fetal and maternal
circulatory systems
Fetal side
Maternal side
Fig. 29-6
Umbilical cord


Connection between fetus and
placenta
Contains the allantois, placental
blood vessels, & yolk stalk of
the yolk sac
Fig. 29-6
Fig. 29-8
Fig. 29-10
Video:
The Miracle of Life