Embryo Stage
?Vernix caseosa, fatty, cheese like
secretion of the fetal sebaceous glands,
covers the skin to protect it from constant
exposure to amniotic fluid.The embryonic disk develops three
layers (germ layers):
*Ectoderm
*Mesoderm
*Endoderm
9.Three cell layers
.1
Ectoderm=
outer
.2
Mesoderm=
middle
.3
Endoderm=
inner
Ecto=
Skin &
nervous
Meso=
Muscles
Bones
Endo=
Digest.E m b r y o g e n e s i s
Fertilization
Cleavage
Oocyte (n)
Zygote
(2n)
2-cell stage
4-cell stage
Sperm
cell (n)
Morula
Blastocyst
G a m e t o g e n e s i s
Ovary Testis
Late
week 3
Early
week 3
Birth
Week 4
Gastrulation
Week 8
Week 5
Organogenesis
?S k i n -- Spinal cord Tail e n d
A m n i o n - Chorionic villi
A m n i o t i c Connecting
fluid s t a l k
Digestive
t r a c t
H e a r t
C h o r i o n
B r a i n Yolk
s a c
E n d o d e r m
E c t o d e r m
M e s o d e r m
*Endoderm
?The outer cells of the morula secrete fluid,
creating a sac of cell (the blastocyst) that has
an inner cell mass placed off-center within the
sac
?The outer layer of blastocyst cells develops
into placenta and fetal membranes.The uterine lining is thick in the upper
uterus preventing the placenta from
attaching so deeply that it does not easily
detach after birth.The upper uterus is richly supplied with
blood for optimal fetal gas exchange and
nutrition.The morula enters the uterus about 3 to 4
days after conception, it stays in the
uterus another 2 to 4 days before
beginning implantation.The external genitalia begin to
differentiate, but male and female
characteristics are not distinct until
after the 10th week.Blood formation occurs primarily in the
liver during the 9th week but shifts to
the spleen by the end of the 12 week.Both vernix and lanugo hair diminish as
the fetus reaches term.A
sperm penetrates
the egg and
conception
occurs.The zygote divides into 2 cells, then 4, then
8cells while in the fallopian tube.The inner cell mass of the blastocyst
develops into the fetus (embryo).Maturation
Copyright (C) The McGraw-Hill Companies , Inc.Embryonic structures continue developing
during implantation.Formation of the placenta
Second week: Implantation is complete by
the end of the 2nd week.The most growth occurs in the
trophoblast, which eventually become the
fetal part of the placenta.Basic structures of all major body organs
are completed during the embryonic
period.Bladder
Copyright (C) The McGraw-Hill Companies, Inc.Lining of gastrointestinal & respiratory
tracts.Tonsils, thyroid, parathyroid, liver,
pancreas.Lining of urinary bladder and urethra
?The neural tube completes closure during
4th week.The first fetal movement begin but are
too slight for the mother to detect.Fetal movement feel like fluttering or
butterflies.???????????????????3.????????????