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An overview of human embryonic development from fertilization to birth, including embryonic age expression, stages of development, implantation, IVF and Preimplantation Genetic Diagnosis, stem cell research, neural tube defects, and problems during fetal period.
Typology: Lecture notes
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2 cells~ 24 hours
58 cells~ 5 days
107 cells~ 6 days
oocyte
fertilised egg
or zygote – 2
nuclei egg and
sperm
2-cell stage 8-cell stage
(3 days)
morula blastocyst
zona
pellucida
trophoblast
or future placenta
inner cell mass or
future embryo
Human embryos in the first week of development
Embryo “hatching”
From the zona
pellucida
Three day old embryos
Three day old embryos
Ectopic
Ectopic
Pregnancies
Pregnancies
The
The ampulla
ampulla of the uterine
of the uterine
tube is the most common
tube is the most common
ectopic
ectopic implantation site.
implantation site.
In vitro fertilisation
In vitro fertilisation
The process by which one or more eggs
The process by which one or more eggs
( (ooooccyytteess)) aarree ffeerrttiilliisseedd oouuttssiiddee tthhee
b booddyy.. FFeerrttiilliissaattiioonn iiss eeiitthheerr aacchhiieevveedd
b byy ppllaacciinngg aa ddrroopplleett ooff wwaasshheedd ssppeerrmm
(~ 50 , 000 ) onto each egg or if the
(~ 50 , 000 ) onto each egg or if the
s sppeerrmm ccoouunntt iiss llooww aa ssiinnggllee ssppeerrmm ccaann
b bee iinnjjeecctteedd iinnttoo eeaacchh eegggg ((IInnttrraa--
C Cyyttooppllaassmmiicc SSppeerrmm IInnjjeeccttiioonn – – IICCSSII))..
at the 6 - 8 cell stage ( 3 - days culture)
at the 6 - 8 cell stage ( 3 - days culture)
b buutt ssoommee cclliinniiccss ccuullttuurree tthhee eemmbbrryyooss
f foorr 55 oorr 66 ddaayyss ttoo eennssuurree hheeaalltthhyy
b bllaassttooccyysstt ssttaaggee eemmbbrryyooss aarree ppllaacceedd
into the uterus.
into the uterus.
oocyte
fertilised egg
(zygote)
blastocyst
4 - cell embryo
Stem Cell Research
themselves for long periods through cell division.
Under certain experimental conditions, they can be
induced to become cells with special functions
such as the beating cells of the heart muscle or the
insulin-producing cells of the pancreas.
inner cell mass – the early embryo.
embryo to obtain stem cells. So they are not
allowed to remove the inner cell mass or totipotent
cells. There is interest in the possibility that at the
8 - cell stage the cells are no longer totipotent but
are still pluripotent (ie can form the 240 + human
cell types).
Multiple Gestations- TWINS
Multiple Gestations- TWINS
About 1 : 80 human births ( 0. 8 %) is a twin pregnancy.
About 1 : 80 human births ( 0. 8 %) is a twin pregnancy.
One third ( 1 : 250 ) are identical twins (monozygotic)
One third ( 1 : 250 ) are identical twins (monozygotic)
a ammnniioonnss,, ttwwoo cchhoorriioonnss,, aanndd eeiitthheerr oonnee ffuusseedd oorr ttwwoo sseeppaarraattee ppllaacceennttaass--
c caannnnoott tteellll ddiiffffeerreennccee bbeettwweeeenn tthheessee ttwwiinnss aanndd ffrraatteerrnnaall uunnttiill ggeenneettiicc
testing is done.
testing is done.
6655 %% ooff MMZZ ttwwiinnss ooccccuurr bbyy ddiivviissiioonn ooff tthhee iinnnneerr cceellll mmaassss aafftteerr ffiirrsstt
week
week
. At this point two embryos will develop with two amniotic sacs, one . At this point two embryos will develop with two amniotic sacs, one
chorionic
chorionic sac and a common placenta.
sac and a common placenta.
IVF has greatly increased the number of fraternal (
IVF has greatly increased the number of fraternal ( dizygotic
dizygotic ) twins and in
) twins and in
22000011 tthhee rraattee ooff ttwwiinnss iinn tthhee UUSSAA wwaass 33 %%..
((aa)) SSeeppaarraattiioonn aatt tthhee ttwwoo
b bllaassttoommeerree ssttaaggee ccaann
lead to twinning.
lead to twinning.
( (bb)) SSpplliittttiinngg ooff tthhee iinnnneerr
cell mass is the most
cell mass is the most
common cause of
common cause of
identical twins.
identical twins.
(c)
(c) Incomplete separation
Incomplete separation
of the inner cell mass
of the inner cell mass
can lead to conjoined
can lead to conjoined
t twwiinnss..
MONOZYGOTIC TWINS
MONOZYGOTIC TWINS
From The Developing Human
From The Developing Human
MMoooorree aanndd PPeerrssaauudd 66
tthh
EEddiittiioonn
From
From Langman
Langman ’
’ s
s Medical Embryology 9
Medical Embryology 9
th
th
Edition
Edition
Lippincott Williams & WilkinsLippincott Williams & Wilkins
Implanted Human
Implanted Human
Blastocyst
Blastocyst
16 days
16 days
gestation
gestation
21 days
21 days
circulation
circulation
established
established
" "TThhee mmoosstt iimmppoorrttaanntt eevveenntt iinn yyoouurr lliiffee iiss nnoott bbiirrtthh,, mmaarrrriiaaggee,,
oorr ddeeaatthh,, bbuutt ggaassttrruullaattiioonn..""-- LL.. WWoollppeerrtt..
Gastrulation
Gastrulation
The inner cell mass in the 15-16 day human embryo
The inner cell mass in the 15-16 day human embryo
consists of two layers
consists of two layers
an upper
an upper epiblast
epiblast and a lower
and a lower
hypoblast.
hypoblast. Gastrulation
Gastrulation converts this
converts this bilaminar
bilaminar disc
disc
into three layers. An upper
into three layers. An upper ectoderm
ectoderm , a middle
, a middle
mesoderm
mesoderm and a lower
and a lower endoderm
endoderm .
.
14 - day embryo Gastrulation in a 16 - day human embryo 18 - day embryo