Development of the Embryo TJC

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Development of the EmbryoTJC
visible embryo even more!
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Developmental Stages and Events
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Objective 1Developmental Stages and Events
The starting points Stage Secondary
Oocyte
Event Ovulation
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Objective 1Developmental Stages and Events
(continued)
When the secondary oocyte completes these 2
events
fertilized ovum
it becomes a (stage 2)
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Objective 1Developmental Stages and Events
(continued)
Within the fertilized ovum genetic material
from the sperm and ovum come together to form a
true 2N cell in an event called
fusion of the pronuclei
That 2N cell formed by fusion of the male and
female pronuclei is the stage (3) known as the
zygote
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Objective 1Developmental Stages and Events
(continued)
The unicellular zygote becomes multicellular(4-5)
in a process, or event, called
cleavage
During cleavage, each generation of daughter
cells produced is smaller in size than the
original cell.
Soon, cleavage produces a solid clump of cells
which resemble a mulberry in appearance.
This stage (5) is the morula.
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Objective 1Developmental Stages and Events
(continued)
Before long, the developing conceptus is no
longer solid. A cavity forms within the
developing cellular mass.
Some of the cells have clearly shown a preference
for location. There is an obvious inner cell
mass and an outer one.
This event is called differentiation (as we now
have some idea about what these cell masses will
become),

and this produces stage(6),
the blastocyst. (cyst - bladder-like or
hollow)
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Objective 1Developmental Stages and Events
(continued)
Whether late morula (as some books claim) or
early blastocyst, by the time the mass enters the
body of the uterus, implantation is not possible
with the fertilization membrane (zona pellucida)
still in place.
Hatching of the blastocyst is the event that
accomplishes the zonas removal.
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Objective 1Developmental Stages and Events
(continued)
IMPLANTATION!!!
IMPLANTATION!!!
IMPLANTATION!!!
IMPLANTATION!!!
IMPLANTATION!!!
IMPLANTATION!!!
IMPLANTATION!!!
IMPLANTATION!!!
IMPLANTATION!!!
IMPLANTATION!!!
AND, contrary to popular folklore, the event that
accomplishes pregnancy is.
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Objective 1Developmental Stages and Events
(continued)
The gestation period in humans is. Put your
pencils down and listen for a minute. All info.
will be repeated!
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Objective 1Developmental Stages and Events
(continued)
Most females are on a 28 day cycle. That
is, if menstruation begins on day 1 of the cycle,
and ovulation takes place on day 14,
then the whole thing is ready for
the reset button by the end of day 28.
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Objective 1Developmental Stages and Events
(continued)
Take that 28 days, multiply by 10 (Yikes!
Pregnancy lasts 10 months???) and you get a
gestation time of 280 days IF YOU START THE COUNT
ON DAY 1. BUT day 1 is the menses, NOT
the day of the oocytes availability.
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14
28
10 X 280
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Objective 1Developmental Stages and Events
(continued)
If the count is started on day 14 (ovulation),
then those first 14 days are eliminated from
the first cycle and the count
becomes
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Objective 1Developmental Stages and Events
(continued)
(Okay, pick up your pencils.)
The gestation period in humans is 266 days from
ovulation, or 280 days from the beginning of the
last menstrual cycle. This is about 38 40
weeks.
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Objective 2Extraembryonic (fetal) membranes
Amnion becomes the amniotic sac Chorion
becomes the fetal part of the
placenta Alantois becomes the umbilical
cord Yolk sac first blood cells and
gametes
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Objective 2Parts of the Placenta

• Chorion
• becomes the fetal part of the placenta
• Decidua basalis
• maternal part of placenta
• portion of endometrium
• decidua means shed

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Objective 3Primary Germ Layers (p. 84)

• ECTODERM
• 1. surface epithelium
• 2. brain and spinal cord
• 3. neural crest cells
• a. peripheral N.S. (most)
• b. face (including muscle and bone)
• MESODERM
• 1. muscle
• 2. connective tissue
• (including dermis and bone)
• ENDODERM
• lining and glandular epithelium
• of digestive tract
• 2. lining and glands of respiratory tract

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Chick Embryo 16 hours
Primitive streak formation of mesoderm (note
darker pink areas surrounding the streak)
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Chick Embryo 25 hours
Somite
Neural groove
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Chick Embryo 72 hours
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