1. Survey of Embryonic
Development

2. Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Diagrams showing the size of a human conceptus from fertilization to the early fetal stage
Fertilization
1-week conceptus
2-week conceptus
Embryo
3-week embryo
4-week embryo
5-week embryo
6-week embryo
7-week embryo
8-week embryo
9-week fetus
12-week fetus

3. Sperm nucleus
Acrosome
Acrosomal
reaction
Granulosa cells
of corona radiata
Zona pellucida
Extracellular
space
Oocyte plasma
membrane
Cortical granule
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Sperm penetration and the cortical reaction (slow block to polyspermy
Sperm
Corona radiata
Zona pellucida
First polar body
Fusion of oocyte
and sperm plasma
membranes
Cortical
reaction
Sperm nucleus engulfed
by oocyte cytoplasm
Oocyte cytoplasm
Oocyte in
second meiotic
division
(a)
(b)

4. (a)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Events immediately following sperm penetration
Daughter
cells
Anaphase of
first cleavage
division
Sperm
Extracellular space
Second meiotic division
of oocyte
Second meiotic division
of first polar body
Detached
sperm tail
Sperm pro-nucleus
Ovum
nucleus
Sperm and ovum
chromosomes
Zygote
Male pronucleus
Mitotic spindle
Centriole
Female pronucleus
Polar
bodies
Corona
radiata
Zona
pellucida
(b)
(c)
(d)
(e)
(f)
(g)
(h)

5. (a) (b) (c) (d) (e)
Sperm
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Degenerating
zona
pellucida
Blastocyst
cavity
Inner cell
mass
Blastocyst
cavity
Trophoblast
Zygote
(fertilized
egg)
4-cell stage
2 days
Morula
3 days
Early blastocyst
4 days
Implanting blastocyst
6 days
Uterus
Ovulation Endometrium
Cavity of
uterus
Ovary
Fertilization
(sperm meets egg)
Uterine tube
Oocyte
(egg)
(a)
(b)
(c)
(d)
(e)
Cleavage from zygote to blastocyst

6. 0 4 8 12 16 20 24 28 32 36
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Hormonal changes during pregnancy
Ovulation
and fertilization
Birth
Human chorionic
gonadotropin
Progesterone
Estrogens
Gestation (weeks)
Relavtive blood levels

7. (a)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Implantation of the blastocyst
Endometrium
Uterine endometrial
epithelium
Inner cell mass
Trophoblast
Blastocyst cavity
Lumen of uterus
Endometrial stroma
with blood vessels
and glands
Syncytiotrophoblast
Cytotrophoblast
Inner cell mass
(future embryo)
Lumen of uterus
(b) (c)

8. Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Future opening
between mouth
and pharynx
Head
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Formation of the three primary germ layers
Bilayered
embryonic disc
Amniotic sac
Yolk sac
Amniotic sac (amnion)
Yolk sac
Cut edge
of amnion
Left
Tail
Primitive
streak Hypoblast
Right
Epiblast
Yolk sac
(b) . . . turned 90˚(c) 3-D view (d) Section view
in (e)
(a) Embryo
(See Figure 28.7b)
(e) Bilayered embryonic disc,
lateral-superior view

9. Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Formation of the three primary germ layers
Head
Cut edge
of amnion
Yolk sac
(cut edge)
Left Right
Sections
Tail
Primitive streak
Primitive
streak
Endoderm
Mesoderm Definitive
endoderm
Epiblast
Hypoblast
Ectoderm
(f) Bilayered embryonic
disc, superior view
(g) 14–15 days
(h) 16 days

10. Head
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Neural Neural groove
fold
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Neurulation
(a) 17 days
(b) 19 days
Amnion
Amniotic cavity
Neural plate
Ectoderm
Mesoderm
Notochord
Endoderm
Surface
ectoderm
Tail Yolk sac
Cut
edge of
amnion
Primitive
streak
Neural
plate
Future
neural
crest
Notochord
Notochord
Cut edge
of amnion
Neural
plate
Primitive
node
Primitive
streak
Neural
groove Neural
crest
Left Right

11. Tissues derived from the three
germinal layers
• Ectoderm: nervous tissues, epidermis
and melanocytes.
• Mesoderm: bones, muscles,
mesenchyme, reproductive system,
urinary system.
• Endoderm: digestive system, respiratory
system, endocrine system.

12. Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Events of placentation, early embryonic development, and extraembryonic membrane formation
Maternal
blood vessels
Lacuna (intervillus
space) containing
maternal blood
Endometrium
Amniotic cavity
Primary
germ layers:
Chorionic villus • Ectoderm
Chorion
Amnion
Yolk sac
Extraembryonic
mesoderm
Chorion
being formed
Lumen of uterus
Proliferating
syncytiotrophoblast
Cytotrophoblast
Amniotic cavity
Bilayered
embryonic
disc:
• Epiblast
• Hypoblast
Endometrial
epithelium
• Mesoderm
• Endoderm
Forming
body stalk
Allantois
Extra-embryonic
coelom
(a) 71/2-day implanting
blastocyst
(b) 12-day implanted
blastocyst
(c) 16-day embryo

13. Embryonic membranes
• Amnion: encases and protects embryo
against mechanical and temperature
trauma.
• Yolk sac: transfers nutrients to embryo.
Replaced by placenta in humans.
• Allantois: repository of embryo wastes.
Replaced by placenta in humans.

14. Events of placentation, early embryonic development, and extraembryonic membrane formation
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Decidua basalis
Maternal blood
Chorionic villus
Umbilical blood
vessels in
umbilical cord
Amnion
Amniotic cavity
Yolk sac
Extraembryonic
coelom
Chorion
Decidua
capsularis
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Lumen
of uterus
(d) 41 / 2 - week embryo

15. Extraembryonic
coelom
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Events of placentation, early embryonic development, and extraembryonic membrane formation
Placenta
Decidua basalis
Chorionic villi
Yolk sac
Amnion
Amniotic
cavity
Umbilical cord
Uterus
Lumen of
uterus
Decidua
capsularis
(f) 13-week fetus

16. Maternal blood
in lacuna
(intervillus space)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Events of placentation, early embryonic development, and extraembryonic membrane formation
Myometrium
Maternal
veins
Maternal
arteries
Umbilical arteries
Umbilical vein
Connection to
yolk sac
Chorionic villus
containing fetal
capillaries
Fetal arteriole
Fetal venule
Amnion
Umbilical cord
(g)
Stratum basalis of
endometrium
Maternal portion
of placenta
(decidua basalis)
Fetal portion of
placenta (chorion)