human embryo

1. Embryonic Development
 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

2. Early Embryonic Development
 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:
 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
Many cells
(solid ball)
BLASTULA
(hollow ball)
Cross section
of blastula
Blastocoel

3. Embryonic Development
 Gastrulation is the
second major phase of
embryonic development
 The cells at one end of the
blastula move inward,
 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

4. Embryonic Development
 The three layers
produced in gastrulation
 Ectoderm, the outer
layer
 Endoderm, an
embryonic digestive
tract
 Mesoderm, which partly
fills the space between
the ectoderm and
endoderm

5. Embryonic Development
 The tissues and organs of a tadpole emerge
from cells of the ectoderm, mesoderm, and
endoderm

6. Embryonic Development
 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.

7. Embryonic Development
 Organs start to form after gastrulation
 Embryonic tissue layers begin to
differentiate into specific tissues and
organ systems

8. Changes in cell shape, cell migration, and
programmed cell death give form to the developing
animal
 Tissues and organs
take shape in a
developing embryo
as a result of
 cell shape changes
 cell migration
Ectoderm

9. Development
 programmed cell
death (apoptosis)
Cell
suicide
Dead cell
engulfed and
digested by
adjacent
cell

10. Embryonic induction initiates organ
formation
 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

11. Pattern formation organizes the
animal body
 Pattern formation is the emergence of a
body form with structures in their correct
relative positions
 It involves the response of genes to spatial
variations of chemicals in the embryo

12. HUMAN DEVELOPMENT
 The embryo and placenta take shape
during the first month of pregnancy
 Gestation is pregnancy
 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

13. HUMAN DEVELOPMENT
 Human development begins with fertilization in
the oviduct
Ovary
Ovulation
Fertilization
of ovum
Cleavage starts
Blastocyst
(implanted
Endometrium
Uterus
Oviduct

14. HUMAN DEVELOPMENT
 Cleavage produces
a blastocyst
 A blastocyst is a
fluid-filled cavity
 The inner cells of
the blastocyst form
the baby
 The outer cells form
the embryo
trophoblast
E
N
D
O
M
E
T
R
I
U
M
ENDOMETRIUM
Cavity
Trophoblast
Inner cell mass

15. HUMAN DEVELOPMENT
 The trophoblast secretes enzymes to enable
the blastocyst to implant in the uterine wall
ENDOMETRIUM
UTERINE CAVITY
Trophoblast
Multiplying cells
of trophoblast
Blood vessel
(maternal
Future
yolk sac
Future embryo

16. HUMAN DEVELOPMENT
 Gastrulation occurs and organs develop from
the ectoderm, endoderm, and mesoderm
Yolk sac
Mesoderm
cells
Amnion
Chorion

17. HUMAN DEVELOPMENT
 Meanwhile, the four
embryonic membranes
develop
 Amnion~fluid filled sac
for protection
 Chorion ~ will form the
embryo’s part of the
placenta
 Yolk sac ~ produces first
blood cells &germ cells
 Allantois ~ will form the
umbilical cord (ropelike
structure that attaches
embryo to uterus)
Yolk sac
Chorion
Amnion
Allantois

18. HUMAN DEVELOPMENT
 The embryo floats in
the fluid-filled
amniotic cavity,
 The placenta’s
chorionic villi absorb
food and oxygen from
the mother’s blood
Placenta
Amniotic
cavity
Chorion
Chorionic
villi
Yolk sac
Mother’s
blood
vessels
Embryo
Amnion

19. Placenta
 Food & gases diffuse across blood vessels

20. HUMAN DEVELOPMENT
 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
 Protective antibodies
 German measles virus
 HIV
 Drugs (prescription and nonprescription)
 Alcohol
 Chemicals in tobacco smoke

21. Human development from conception to
birth is divided into three trimesters
 First trimester
 First three months
 The most rapid changes occur during the first
trimester
 7 weeks 10 weeks
4 weeks

22. Human development from conception to
birth is divided into three trimesters
 Second trimester
 Increase in size of fetus
 General refinement of human features
12 weeks

23. Human fetal development
 The fetus just spends much of the 2nd & 3rd
trimesters just growing
…and doing various flip-turns & kicks inside
amniotic fluid
Week 20

24. Human fetal development
 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

25. Human fetal development
 30 weeks (7.5 months)
umbilical cord

26. Getting crowded in there!!
 32 weeks (8 months)
The fetus sleeps 90-
95% of the day &
sometimes
experiences REM
sleep, an indication
of dreaming

27. Human development from conception to
birth is divided into three trimesters
 Third trimester
 Growth and
preparation for birth

28. Childbirth is hormonally induced and
occurs in three stages
 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

29. Positive feedback Mechanism
 Oxytocin is a powerful
stimulant for the smooth
muscles of the uterus
 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

30. Birth
positive feedback

31. Three stages of labor
 1.Dilation of the
cervix is the first
stage
-Cervix reaches full
dilation at 10cm
 Longest stage of
labor (6-12 hours or
longer)
Dilation of the cervix

32. Three stages of labor
 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

33. Three stages of labor
 The delivery of the
placenta is the final
stage of labor
 Usually occurs
within 15 minutes
after the birth of the
baby

34. The end of the journey!
And you think
9 months of
Biology is hard!

35. Childbirth is hormonally induced and
occurs in three stages
 Hormones continue to be important after
the baby and placenta are delivered
 Decreasing progesterone and estrogen
levels allow the uterus to return to its pre-
pregnancy state
 Oxytocin and prolactin stimulate milk
secretion

36. Reproductive technology increases
our reproductive options
 Reproductive technology
 Hormone therapy can
increase sperm or egg
production
 Surgery can correct
blocked oviducts
 Assisted reproductive
technology
 In vitro fertilization
(IVF)
 Surrogate motherhood