Transcript Embryonic Development

Embryonic Development
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Development: series of orderly, precise steps that
transform a zygote into a multicellular embryo ~early
stage of development of multicellular organism
Includes:
1. cell division
2. cell growth
3. cell differentiation
~changing of unspecialized embryonic cells into
specialized cells, tissues,& organs
Early Embryonic Development
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Cleavage is the first major
phase of embryonic
development
 It is the rapid succession
of cell divisions (Mitotic)
 It creates a multicellular
embryo from the zygote
 NO growth
 Stages:
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1. Morula~solid ball of
cells
2.Blastula~ single layer
of cells surrounding a
fluid-filled cavity called
the blastocoel
ZYGOTE
2 cells
4 cells
8 cells
Blastocoel
Many cells
(solid ball)
BLASTULA
(hollow ball)
Cross section
of blastula
Embryonic Development
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Gastrulation is the
second major phase of
embryonic development
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The cells at one end of the
blastula move inward,
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It adds more cells to
the embryo
It sorts all cells into
three distinct cell layers
The embryo is
transformed from the
blastula into the
gastrula
Embryonic Development
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The three layers
produced in gastrulation
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Ectoderm, the outer
layer
Endoderm, an
embryonic digestive
tract
Mesoderm, which partly
fills the space between
the ectoderm and
endoderm
Embryonic Development
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The tissues and organs of a tadpole emerge
from cells of the ectoderm, mesoderm, and
endoderm
Embryonic Development
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ectoderm cells~ eventually
they develop into the skin and
nervous tissue of the animal
endoderm cells ~develop into
the lining of the animal’s
digestive tract and into
organs associated with
digestion.
mesoderm cells ~develop
into the muscles, circulatory
system, excretory system,
and, in some animals, the
respiratory system.
Embryonic Development
Organs start to form after gastrulation
 Embryonic tissue layers begin to
differentiate into specific tissues and
organ systems
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Changes in cell shape, cell migration, and
programmed cell death give form to the developing
animal
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Tissues and organs
take shape in a
developing embryo
as a result of
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cell shape changes
cell migration
Ectoderm
Development
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programmed cell
death (apoptosis)
Cell
suicide
Dead cell
engulfed and
digested by
adjacent
cell
Embryonic induction initiates organ
formation
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Induction is the mechanism by which one
group of cells influences the
development of tissues and organs from
ectoderm, endoderm, and mesoderm
Adjacent cells and cell layers use chemical
signals to influence differentiation
 Chemical signals turn on a set of genes
whose expression makes the receiving cells
differentiate into a specific tissue
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Pattern formation organizes the
animal body
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Pattern formation is the emergence of a
body form with structures in their correct
relative positions
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It involves the response of genes to spatial
variations of chemicals in the embryo
HUMAN DEVELOPMENT
The embryo and placenta take shape
during the first month of pregnancy
 Gestation is pregnancy
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It begins at conception and continues until
birth
 Human gestation is 266 days
(38 weeks or 9 months)
 Mouse gestation is 1 month
 Elephant gestation is 22 months
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HUMAN DEVELOPMENT
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Human development begins with fertilization in
the oviduct
Cleavage starts
Fertilization
of ovum
Ovary
Oviduct
Ovulation
Blastocyst
(implanted
Endometrium
Uterus
HUMAN DEVELOPMENT
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Cleavage produces
a blastocyst
 A blastocyst is a
fluid-filled cavity
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The inner cells of
the blastocyst form
the baby
The outer cells form
the embryo
trophoblast
ENDOMETRIUM
E
N
D
O
M
E Inner cell mass
T
R
Cavity
I
U
M
Trophoblast
HUMAN DEVELOPMENT
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The trophoblast secretes enzymes to enable
the blastocyst to implant in the uterine wall
ENDOMETRIUM
Future embryo
Blood vessel
(maternal
Multiplying cells
of trophoblast
Future
yolk sac
Trophoblast
UTERINE CAVITY
HUMAN DEVELOPMENT
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Gastrulation occurs and organs develop from
the ectoderm, endoderm, and mesoderm
Amnion
Mesoderm
cells
Chorion
Yolk sac
HUMAN DEVELOPMENT
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Meanwhile, the four
embryonic membranes
develop
Chorion
 Amnion~fluid filled sac
for protection
Amnion
 Chorion ~ will form the
embryo’s part of the
placenta
Yolk sac
 Yolk sac ~ produces first
blood cells &germ cells
 Allantois ~ will form the
umbilical cord (ropelike
structure that attaches
embryo to uterus)
Allantois
HUMAN DEVELOPMENT
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The embryo floats in
the fluid-filled
amniotic cavity,
Placenta
The placenta’s
Yolk sac
chorionic villi absorb
food and oxygen from
the mother’s blood
Mother’s
blood
vessels
Amniotic
cavity
Amnion
Embryo
Chorion
Chorionic
villi
Placenta
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Food & gases diffuse across blood vessels
HUMAN DEVELOPMENT
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Embryonic development of essential organs occur in early
pregnancy
The embryo may encounter risks from faults in its genes & from
mother’s exposure to environmental factors
The placenta allows for a variety of substances to pass from
mother to fetus
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Protective antibodies
German measles virus
HIV
Drugs (prescription and nonprescription)
Alcohol
Chemicals in tobacco smoke
Human development from conception to
birth is divided into three trimesters
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First trimester
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First three months
The most rapid changes occur during the first
trimester
4 weeks
7 weeks
10 weeks
Human development from conception to
birth is divided into three trimesters
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Second trimester
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Increase in size of fetus
General refinement of human features
12 weeks
Human fetal development
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The fetus just spends much of the 2nd & 3rd
trimesters just growing
…and doing various flip-turns & kicks inside
amniotic fluid
Week 20
Human fetal development
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24 weeks (6 months; 2nd trimester)
fetus is covered with
fine, downy hair
called lanugo. Its skin
is protected by a
waxy material called
vernix
Human fetal development
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30 weeks (7.5 months)
umbilical cord
Getting crowded in there!!
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32 weeks (8 months)
The fetus sleeps 9095% of the day &
sometimes
experiences REM
sleep, an indication
of dreaming
Human development from conception to
birth is divided into three trimesters
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Third trimester
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Growth and
preparation for birth
Childbirth is hormonally induced and
occurs in three stages
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Hormonal changes induce birth
Labor is controlled by a positive feedback
mechanism
 Estrogen released from the ovaries
increases the sensitivity of the uterus to
oxytocin
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Positive feedback Mechanism
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Oxytocin is a powerful
stimulant for the smooth
muscles of the uterus
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Oxytocin also
stimulates the placenta
to make prostoglandins
that stimulate the
uterine muscles to
contract even more
Uterine contractions
stimulate the release of
more and more oxytocin
and prostoglandins
positive feedback
Birth
Three stages of labor
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1.Dilation of the
cervix is the first
stage
-Cervix reaches full
dilation at 10cm
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Longest stage of
labor (6-12 hours or
longer)
Dilation of the cervix
Three stages of labor
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Expulsion is the second stage
 Period from full dilation of
the cervix to delivery of
the infant
 Uterine contractions occur
every 2-3 minutes
 Mother feels urge to push
down with her abdominal
muscles
 Infant is forced down and
out of uterus and vagina
within a period of 20
minutes
Three stages of labor
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The delivery of the
placenta is the final
stage of labor
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Usually occurs
within 15 minutes
after the birth of the
baby
The end of the journey!
And you think
9 months of
Biology is hard!
Childbirth is hormonally induced and
occurs in three stages
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Hormones continue to be important after
the baby and placenta are delivered
Decreasing progesterone and estrogen
levels allow the uterus to return to its prepregnancy state
 Oxytocin and prolactin stimulate milk
secretion
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Reproductive technology increases
our reproductive options
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Reproductive technology
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Assisted reproductive
technology
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Hormone therapy can
increase sperm or egg
production
Surgery can correct
blocked oviducts
In vitro fertilization
(IVF)
Surrogate motherhood