i want 30 multiple choice questions that covers different aspects of all of the following information with their model answer below each question : Objectives
By the end of this lecture student should be able to: Study the 3rd week of development (trilaminar disc)Contents
-Formation of the prechordal plate.
-Formation of the notochord.
-Formation of the neuroenteric canal.
-Formation of the allantois.
-Development of the trophoblast.Formation Of
Prechordal Plate
(mesoderm)
& NotochordBilaminar embryonic discBilaminar embryonic discTrilaminar embryonic discTrilaminar embryonic disc
Ectoderm
Endoderm
MesodermSome of the first
cells that migrate
through the
primitive node
Formation of the prechordal plate
Primitive node
form a thickened
plate, it is called
the prechordal
plate.Formation of the prechordal plate
Some of the first cells
that migrate through
the primitive node
form a thickened
plate, it is called the
prechordal plate.
Prechordal plateFormation of the prechordal plate
-The prechordal
plate is important
for induction of the
forebrain.
Prechordal plateFormation of the notochord
- Some of the cells
that invaginate
the primitive node
are called
Prenotochordal
cells .
-They move
cranially in the
midline until they
reach the
prechordal plate.
Prenotochordal cellsFormation of the notochord
- Some of the cells
that invaginate
the primitive node
are called
Prenotochordal
cells .
-They move
cranially in the
midline until they
reach the
prechordal plate.Formation of the notochord
- Some of the cells
that invaginate the
primitive node are
called Prenotochordal
cells .
-They move cranially
in the midline until
they reach the
prechordal plate.
Prechordal plateFormation of the notochord
-Prenotochordal
cells form a solid
cord of cells,
it is called the
definitive
notochord.
Definitive notochordFormation of the notochord
Primitive Pit
-The notochord
extends cranially to
the prechordal
plate and caudally
to the primitive pit.
Prechordal plate
Definitive notochordCross section
Notochord
(Arrow)
Amniotic cavity
Formation of the notochord
Ectoderm
Mesoderm
Endoderm
Yolk sacFormation of the notochord
-The notochord is a
signaling center for
inducing the axial
skeleton.Formation Of
Neuroentric Canal
& AllantoisFormation of the neuroenteric canal
Primitive pit
(neuroenteric canal)
-At the primitive pit
an indentation is
formed in the epiblast
-It forms a temporary
canal that connects
the amniotic cavity
and the yolk sac
(neurenteric canal).
Yolk sac
Amniotic cavityFormation of the neuroenteric canal
-At the primitive pit
an indentation is
formed in the epiblast
-It forms a temporary
canal that connects
the amniotic cavity
and the yolk sac
(neurenteric canal).
Yolk sac
Amniotic cavityAllentoentric diverticulum (Allantois)
Connecting stalk
Yolk sacAllentoentric diverticulum (Allantois)
-By the 16th day the wall
of the yolk sac forms a
small diverticulum that
extends into the
connecting stalk.
-It is called
allantoenteric
diverticulum (allantois)
Connecting stalk
AllantoisAllentoentric diverticulum (Allantois)
Connecting stalk
-In lower vertebrates:
The allantois serves as
a reservoir for urine.
-In humans:
.It remains rudimentary.
.Part of the allantois
remains in the connecting
stalk and part is involved
in the development of
the urinary bladder.
AllantoisDevelopment
of trophoblastPlacental villi
Syncytiotrophoblast
Cytotrophoblast
Extraembryonic
somatic mesoderm
(chorionic plate)
Development of trophoblastDevelopment of trophoblast
The trophoblast form
the placental villiPrimary Villi
Development of trophoblast
-By the beginning of
the third week, the
trophoblast is
characterized by
primary villi.
-The primary
villous is formed of
a cytotrophoblastic
core covered by a
syncytial layer.
Syncytiotrophoblast
CytotrophoblastSecondary Villi
-When the
mesodermal cells of
the chorionic plate
penetrate the core of
primary villi, they are
called secondary villi.
-The secondary villous
is formed of a
mesodermal core
covered by a
cytotrophoblast and
syncytial layers.
Chorionic plate
Development of trophoblast
Syncytiotrophoblast
Cytotrophoblast
MesodermTertiary Villi
Development of trophoblast
-By the end of the third
week mesodermal cells in
the core of the villi
differentiate into blood
cells and small blood
vessels, forming the villous
capillary system.
-The villi is now known as
tertiary villi or definitive
placental villi.
Syncytiotrophoblast
Cytotrophoblast
Villus
capillaryDevelopment of trophoblastDevelopment of trophoblast
Tertiary villi
Capillaries in tertiary
villi are connected
with capillaries in the
mesoderm of the
chorionic plate and in
the connecting stalk
and with the
intraembryonic
circulatory system
Chorionic
plate
Connecting
stalk-The heart begins to
beat in the fourth
week of development.Day 19 & 20 Development of trophoblast
The chorionic cavity enlarges