Download Embryonic Development

Exercise 46
Embryonic
Development
Developmental stages of
humans
Fertilization
 Zygote
 It is a fertilized egg
 Diploid (2n)
 Female pronuclei
 Male pronuclei
 Amphimixis

Developmental stages of
humans
Zona pellucida
 Surrounds the zygote
 Disappears when the blastocyst
reaches the uterine cavity
 Corona radiata
 Granulosa cells surrounding the
zona pellucicda
 Disappears after fertilization

Fertilization
Developmental stages of
humans
Cleavage
 Stages of the Cleavage
 Blastomere
 Early cleavage
 4-cells stage…
 Morula
 16-32 cells stage

Developmental stages of
humans


Blastocyst
 Central cavity appears – blastocystic
cavity
 Inner cell mass (ICM) – forms the embryo
 Trophoblast – nourishes the developing
embryo
Final product of cleavage
Developmental stages of
humans

Implantation
 From day 7 to day 10 after the
ovulation
 The blastocyst will go from a floating
stage to a complete implanted stage
in the uterus
Developmental stages of
humans
Gastrulation
 The ICM will develop into three
primary germ layers
 Ectoderm
• Forms the epithelia and nervous
system

Developmental stages of
humans
 Mesoderm
• Forms everything between the
ectoderm and the endoderm
 Endoderm
• Forms the mucosa of the digestive
and respiratory tract, etc
Endometrium will form the
deciduas



Deciduas basalis-part of the
endometrium that forms the maternal
portion of the placenta
Deciduas capsularis – the rest of the
endometrium surrounding the embryo
Deciduas parietalis – endometrium not
surrounding embryo or placenta
Developmental stages
Developmental stages of
humans
Embryo
 0 to 8 weeks
 Fetus
 9 weeks to birth
 Trophoblast
 Will develop villi
 Will differentiate into the chorion that
will form the fetal portion of the
placenta

Developmental stages of
humans
Placenta
 Chorionic villi + decidua basalis
 Embryonic membranes (from the ICM)
 Amnion
• Encases the embryo
• Amniotic cavity
• Amniotic fluid

Developmental stages
Developmental stages of
humans
 Yolk
sac
• Originates the embryo’s first blood
cells
 Allantois
• Body stalk and later umbilical cord
• Umbilical cord attaches the
embryo to the placenta
In uterus development

Placenta
 Fetal side
• Shine and smooth
• Presence of large blood vessels
 Maternal side
• Spongy, torn-looking, rough