Intro 28: Gastrulation & formation of Tri-Laminar Disc Flashcards
(61 cards)
Anatomic terms for Embryo
Superior=
Inferior=
Anterior=
Posterior=
Sagittal=
Coronal=
Superior= =CRANIAL, CEPHALIC
Inferior= CAUDAL
Anterior= VENTRAL
Posterior= DORSAL
Sagittal= MEDIAN
Coronal= FRONTAL
When does GASTRULATION occur
WEEK 3
of embryonic development
GASTRULATION is the process by which…
Bi-laminar embryonic disc is converted into a TRI-LAMINAR EMBRYONIC DISC
TRI-LAMINAR EMBRYONIC DISC contains 3 GERM LAYERS:
ECTODERM
MESODERM
ENDODERM
- will give rise to
all specific tissues and organs
Gastrulation is the beginning of
MORPHOGENESIS
(development of the form
and structure of various organs and parts of the body)
Gastrulation begins with the formation of a transient structure called…
on what day
PRIMITIVE STREAK
- DAY 15
PRIMITIVE STREAK is formed by the THICKENING of…
THICKENING of EPIBLAST CELLS
- first appears at CAUDAL end (cells in median area will start to proliferate at caudal end)
- elongates into primitive groove
- MIGRATES towards CRANIAL end (towards prechordal plate)
formation of primitive streak establishes the..
cranial/caudal axis of the embryo
At the CRANIAL end of primitive streak EPIBLAST cells ingress at
a greater rate forming a CIRCULAR CAVITY called..
PRIMITIVE PIT
cells of the PRIMITIVE STREAK PROLIFERATE and become
ENLARGED to form the…
PRIMITIVE NODE
– primary
tissue organiser
EPITHELIAL cells in the lateral edge of the EPIBLAST undergo…
EMT
-epithelial to MESENCHYMAL
transition
What happens to the epithelial cells that undergo EMT
become flask-shaped,
detach,
MIGRATE DOWN/INTO PRIMITIVE STREAK
(INVAGINATION / INGRESSION)
The FIRST set of epithelial cells of epiblast to move down primitive streak INTEGRATE INTO HYPOBLAST LAYER and REPLACE it to form…
ENDODERM
(1st germ layer to be formed)
The SECOND set of epithelial cells to detach and ingress FILL
the SPACE between ENDODERM and EPIBLAST, which forms…
MESODERM
(middle layer)
What do the REMAINING epiblast cells that don’t migrate into primitive streak form
ECTODERM
How is gastrulation regulated?
Through regulation of gene expression
Examples:
- FGF8 secreted by the node and p.s. induce the expression of a
gene called Nodal that is involved in initiating and maintaining the
primitive streak
- BMP4 (bone morphogenic protein 4) is secreted throughout the
embryonic disk and together with FGF8 will drive ventralization of
the mesoderm - Chordin, noggin and follistatin antagonise the activity of BMP4
and as a result cranial mesoderm is dorsalized into notochord,
somites and somitomeres - left-right body axis is established through a signalling cascade and
differential expression of genes on the left and right side
Examples of Gastrulation Abnormalities
Caudal dysgenesis (sirenomelia):
- insufficient mesoderm is formed in the caudalmost region of the embryo
- as a result abnormalities in the lower limbs and urogenital system
Sacrococcygeal teratomas:
- tumours that occur when reminants of the primitive streak persist in the
sacrococcygeal region
(most common tumour in newborns: 1/37000)
What 2 things happen in the 3rd week
- Gastrulation
- Development of the NOTOCHORD
Day 18 –21 Development of the notochord:
Progenitor mesoderm (mesenchymal) cells from the primitive node and pit migrate to form a..
median cellular cord
–the NOTOCHORDAL PROCESS
the NOTOCHORDAL PROCESS soon acquires a lumen called..
NOTOCHORDAL CANAL
DAY 18-21
The primitive streak regress…
as the notochordal process advances…
caudially
cranially between the ectoderm
and endoderm until it reaches the prechordal plate
day 18-21:
Some mesenchymal cells from the primitive streak migrate cranially and meet to form the CARDIOGENIC MESODERM in the…
CARDIOGENIC AREA/PLATE
CARDIOGENIC AREA/PLATE is where the…
PRIMORDIUM of the HEART begins to develop
at the END of the 3RD WEEK
day 18-21:
As the hypoblast is replaced by endoderm cells (gastrulation) what happens to the NOTOCHORDAL PROCESS and what is formed?
NOTOCHORDAL PROCESS cells PROLIFERATE and DETACH from endoderm to form NOTOCHORDAL PLATE
