Intro 28: Gastrulation & formation of Tri-Laminar Disc Flashcards
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
DAY 18-21
NOTOCHORDAL PLATE will ultimately form a solid cylinder of cells called:
NOTOCHORD
what is the NOTOCHORD and its functions (4)
a transient structure that:
- provides SUPPORT
- defines the AXIAL AXIS for the embryo (serves as the basis for the development of the AXIAL SKELETON)
- induces the overlying embryonic ectoderm to thicken and form the NEURAL PLATE (the primordium
of the central nervous system) - Indicates the future sites of the vertebral bodies
Fused layers of ectoderm and endoderm form the…
-OROPHARYNGEAL MEMBRANE
(located at the future site of the
oral cavity)
- CLOACAL MEMBRANE
(at the future site of the anus)
Specific regions of the epiblast migrate through different parts of the node and primitive streak to form mesoderm:
Cells migrating at the CENTRAL and most CRANIAL part of the node will form the…
NOTOCHORD
Specific regions of the epiblast migrate through different parts of the node and primitive streak to form mesoderm:
Cells migrating more POSTERIORLY will form
PARAXIAL MESODERM
(pm; somitomeres and somites)
Specific regions of the epiblast migrate through different parts of the node and primitive streak to form mesoderm:
The next region will form…
INTERMEDIATE MESODERM
(im; urogenital system)
Specific regions of the epiblast migrate through different parts of the node and primitive streak to form mesoderm:
Cells migrating through the MORE CAUDAL part of the streak will form…
LATERAL PLATE MESODERM
(lpm; body wall)
Specific regions of the epiblast migrate through different parts of the node and primitive streak to form mesoderm:
Cells migrating through the MOST CAUDAL part will contribute to…
EXTRAEMBRYONIC MESODERM
(eem; chorion)
Blastomeres differentiate into…
Trophoblast
Embryoblast / ICM
Embryoblast differentiate into…
Epiblast
Hypoblast
Epiblast differentiate into…
Endoderm
Mesoderm
Ectoderm
Derivatives of MESODERM
HEAD
PRAXIAL MESODERM
INTERMEDIATE MESODERM
LATERAL MESODERM
see diagram
Derivatives of ECTODERM
SURFACE ECTODERM
NEUROECTODERM -Neural Crest, Neural Tube
see diagram
The placenta is a…
materno-foetal organ
(some derived from maternal tissue, some derived from foetal tissue)
The placenta provides…
- nutrition
- gas exchange
- waste removal
- source of haematopoietic cells
- endocrine
- immune support
Stages of PLACENTA DEVELOPMENT
(0,1,2,3,4)
0 –Lacunar stage
1 –Primary villus
2 –Secondary villus
3 –Tertiary villus
4 –Free villus and cytotrophoblast layer
at DAY 9-10 what appear in syncytiotrophoblasts (which are proliferating and invading)
vacuoles appear in syncytiotrophoblasts which fuse to form LANUNAE
(spaces between STs)
DAY 9-10
As syncytiotrophoblasts invade further what do they meet
meet MATERNAL CAPILLARIES which are eroded by syncytiotrophoblasts
- syncytiotrophoblasts fill LACUNAE with blood from maternal capillaries
At around DAY 13, what is formed
PRIMITIVE UTERO-PLACENTAL CIRCULATORY SYSTEM
(1st contact between blood of mother and tissue of embryo)
how is the PRIMITIVE UTERO-PLACENTAL CIRCULATORY SYSTEM formed at day 13
Cytotrophoblasts grow into the Lacunae as the PRIMARY CHORIONIC VILLI
(small projects of cytotrophoblasts begin to expand into syncytiotrophoblast)
What is formed at DAY 16
SECONDARY CHORIONIC VILLI
how is the SECONDARY CHORIONIC VILLI formed
from day 14-16
- Primary chorionic villi begin to BRANCH
- EXTRAEMBRYONIC MESODERM INVADES (grows into primary villi)
What happens at the end of the 3rd week / DAY 21 and what is formed
EMBRYONIC BLOOD VESSELS (foetal capillaries) begin to form in the extra-embryonic MESODERM of the Secondary Villi
- formed the TERTIARY CHORIONIC VILLI
Placental Barrier has 4 layers:
- EXTRA-EMBRYONIC MESODERM
- CYTOTROPHOBLAST
- SYNCYTIOTROPHOBLAST
- FOETAL CAPILLARIES
EMBRYONIC BLOOD VESSELS in/invading the tertiary villus:
UMBILICAL ARTERIES
- carry the DEOXYGENATED blood from the embryo to the placenta
UMBILICAL VEIN
- returns the OXYGENATED blood to the embryo
(other way round)
embryo
by the end of the 4TH WEEK:
a complex vascular network develops in the placenta allowing…
maternal-embryonic exchanges
Until the beginning of the 8th week, CHORIONIC VILLI will…
cover the entire CHORIONIC SAC
At 8th week, what happens to CHORIONIC VILLI covering CHORIONIC SAC?
- some will degenerate producing the SMOOTH CHORION
-those in close proximity to the DECIDUA BASALIS will form the VILLOUS CHORION / CHORION FRONDOSUM
What is the DECIDUA BASALIS
(derived from decidua)
the maternal part of the placenta
The UMBILICAL CORD connects what…
connects PLACENTA to EMBRYO
What does the umbilical cord contain:
2 UMBILICAL ARTERIES
1 UMBILICAL VEIN
What does the umbilical cord contain:
2 UMBILICAL ARTERIES
1 UMBILICAL VEIN
When is the PLACENTA and EMBRYO formed
at 8 WEEKS
4 FUNCTIONS OF PLACENTA
- Exchange of gases
(eg oxygen, carbon dioxide and
carbon monoxide) - Exchange of nutrients and electrolytes
(amino acids, free fatty acids,
carbohydrates and vitamins)
-Transmission of maternal antibodies
-Hormone production
Transmission of maternal antibodies at around WEEK 14
immunoglobulins consist almost entirely of maternal IgG,
which begins to be transported from mother to foetus at 14 weeks
- Passive Immunity
Hormone production in placenta
- by end of the 4th month the placenta produces
PROGESTERONE:
necessary for maintenance of pregnancy - Increasing amounts of ESTROGENS:
stimulate uterine growth and development of mammary
glands - SOMATOMAMMOTROPIN (hPL – human Placental Lactogen) :
gives foetus priority on maternal blood glucose
promotes breast development for milk production
Examples of Abnormalities related to development of placenta
PLACENTA PREVIA
- The placenta overlies internal
os of uterus, covering the birth
canal
- 1/200-250 pregnancies
PLACENTA ACCRETA
- Abnormal adherence, with
absence of decidua basalis
- 3/1000 deliveries
