Unit 1.L2-Gastrulation,Trilaminar Embryo and Organogenetic Period Flashcards
3.5 week
What disappears and what developes surrounded by the trophoblast cells?
The primary umbilical vesicle disappears & the secondary umbilical vesicle develops surrounded by the trophoblast cells (calipers).
What are the symptoms of pregnancy?
What happens when bleeding is interpreted as menstruation?
an error occurs in determining the expected delivery date of the fetus
What is the origin of germ layers and extra embryonic tissues?
What defines embryonic Cranial-Caudal directionality?
Prechordal plate
What always forms at the end of week 2?
secondary umbilical vesicle (yolk sac) forms and enlarges
What is a key step in week 3
gastrulation
- What is gastrulation?
- What does it begin with?
- Gastrulation is the conversion of the epiblast (bilaminar into a trilaminar embryonic disc consisting of endoderm, mesoderm, and ectoderm”.
- begins with the formation of the primitive streak
When does morphogenesis begin?
end of D14
What is the result of gastrulation?
the three germ layers & PGCs
- 3-germ layers instructs the formation of adult body plan & all body tissues
What is the process of initation of gastrulation entails? (caudally and cranially)
The primitive streak elongates how and from what?
The primitive streak elongates “medially (caudal->cranial) from the thickened dorsal epiblast surface of the bilaminar embryo
How does the bilaminar embryonic disc goes to trilaminar embryonic disc?
- Primitive streak gives rise to the Mesoderm layer
- The Epiblast is now called the “Ectoderm layer”
- The Hypoblast is replaced by “Endoderm layer
Axial Orientation is Established:
Cranio-Caudal & Dorso-Ventral axis gives “bilateral symmetry” to the embryo.
- Cranial Side: Prechordal plate
- Caudal Side: Primitive streak
- Dorsal Side: Ectoderm
- Ventral side: Hypoblast->Definitive Endoderm
- What does the caudal end of the primitive streak do?
- What does the cranial end of primitive streak form?
- Caudal end of Primitive streak elongates by cell proliferation
- Cranial end of primitive streak has continuous cell proliferation that “pile-up” to form the primitive node
All cells are destined to go to the prechrondal plate but also in
How is the primitive groove formed?
by medial invagination of epiblast cells. It is a narrow linear depression within the primitive streak.
How is the primitive pit formed?
is formed by a depression (cranially) in the primitive node
What does the primitive streak cells do to become mesoblast?
Primitive streak cells “ingress” between the epiblast & hypoblast and become mesoblasts( between epi and hypoblasts)
What is ingression?
vital step for epiblast to change to squamos (spindly) so they can move inside
Definitive embryonic endoderm formation:
Cells from the epiblast, primitive node & primitive streak, displace the hypoblast, forming definitive embryonic endoderm cells in the roof of the umbilical vesicle
What does The remaining dorsal epiblast cells form?
Embryonic ectoderm
Where are the mesoblasts? what do they give rise to?
The Mesoblasts are sandwiched, forming the middle layer, which gives rise to: “Intraembryonic Mesoderm”
The three germ layers form what?
trilaminar embryo
What do cells move through?
primitive pit
What is displaced to extraembryonic regions, forming the wall of the umbilical vesicle?
hypoblast cells
Where does the mesoderm cells in the primitive node migrate to and form?
Move to top by going down in the pit under the epiblast
Cranially, the “mesoderm cells” in the primitive node migrate to form the notochordal process. (top arrows)
Primitive node cont to grow towards what?
prechordal plate
The cells from the Primitive pit continue to move where?
move ventrally towards the hypoblast
What does the primitive pit allow?
What is the mesoblast migration pattern?
What defines the future mouth?
Notochordal process at Prechordal plate defines future mouth; the Stomodeum.
What forms the future mouth?
Cranially, at the Stomodeum, ectoderm fuses to the endoderm, forming the oropharyngeal membrane, which dissolve to form the future mouth.
What forms the primodial anus or proctodeum?
Caudally, the ectoderm fuses to the endoderm, forming the cloacal membrane, which dissolves to form the primordial anus; the Proctodeum
The notochordal process grows so fast until it touches what? what happens
touch precordial plate, oropharyngeal membrane when noto touches
T/F: nonchordal process is endoderm origin?
False: mesoblast
What happens to the primitive steak to effect notochordal process?
- Primitive streak shortens but adds cells to elongate the notochordal process
- The notochordal process lengthens by cranial migration of mesodermal cells from the node under the epiblast
the (notochordal process + adjacent underlying mesoderm) =
induce the overlying “embryonic ectoderm FIELD” to form the neural plate->(future CNS).
What does morphigins and mesodermal cells on the side form?
Notochordal process grows how? Then what does it do?
- The notochordal process grows cranially under the embryonic ectoderm at the primitive pit until it reaches the Prechordal plate.
- Notochordal process splits ( and mouth)
Notochordal process “splits” under the ectoderm & forms what?
- Lumen (the notochordal canal)
- Roof-layer of NC
- Floor-layer of NC
The Roof-layer of NC touches what? to induce what?
The Roof-layer of NC touches embryonic ectoderm to induceàNeural Plate (future CNS).
How does Notochord Originates from the Notochordal process?
- Floor-layer of the Notochordal Canal (NC) fuses with the embryonic endoderm, forming two layered floor.
- Then, both layers degenerate (Floor-layer of NC +Endoderm), thus the Roof-layer of NC touches the umbilical vesicle
After the floor layer of NC and endoderm degrades, primitive pit forms what?
The Primitive pit forms the Neurenteric canal linking the amniotic and umbilical vesicle cavities.
How do you form grooved notochordal plate?
Roof-layer of the notochordal canal flattens
What closes that neurenteric canal?
Cranial cell proliferation in the notochordal plate causes infolding, creating a cylindrical Notochord across the embryo
The notochord is the main inducer, driving what?
organ induction.
General neurulation?
“Infolding” of the Notochordal plate forms what?
forms a tube; the Notochord
Notochord induces the top ectoderm to thicken & form what?
nerual plate
What does the neural plate (neuroectoderm) form
forms CNS, brain, spinal cord & retina
As the notochord elongates, the neural plate broadens how?
cranially (below)
Neural plate goes down to ?
primitive node
The neural plate invaginates along its central axis to form what?
a neural groove flanked by neural folds
The neural folds become prominent where? What does it initate?
The neural folds become prominent at the cranial end, initiating brain development
The Neural folds begin to move together to form what?
- Neural Groove, which fuse both ends of the neural folds by day 21
- WHen the epiblast move to the sides as the neural groove forms, they will become aminoblast, no longer ecto or neuroecto cells
Neural tube forms the primordium of the:
(1) Brain vesicles &
(2) Spinal cord
Because of the utube (horseshoe cavity), it gives rise to what?
somatopleure (mesoderm+ectoderm) and splanchopleure (mesoderm+endoderm)
What does the splanchopleure form?
gut tube
Base of splanchopleure cells, start forming cardiogeneis mesodermal cells
What shows up at day 21?
3 somites formed from paraxial mesoderm
What is utube?
Horse show shaped canal which is imp for formation of blood islands and cardiogen. mesoderm
How does utube formed?
lacuae of intraembryonic coelom forms the utube
- Neural fold is flanked by what?
- Neural folds fuse and the nerual crest cells migrate how?
- Neural crest via?
- Neural fold is flanked by neural crest cells
- Neural folds fuse & the cells migrate ventro-laterally
- Neural Crest via epithelial to mesenchymal transition (EMT) (move out away from neural tissue) migrate into the mesodermal layer-> more lateral dorsal and form ganglia on both sides
How is the continuous epidermis later formed?
Surface ectoderm becomes delaminated and fuses to form
Neural crest cells further migrate laterally, forming the
spinal ganglia
The paraxial mesoderm (PM), emerges from what? What does it become?
The paraxial mesoderm (PM), emerges from the primitive node between the neuroectoderm and endoderm & laterally becomes intermediate mesoderm & lateral mesoderm
Lateral mesoderm is continuous with what?
umbilical vesicle (bottom) and amnion (top)
the paraxial mesoderm differentiates, condenses, & divides into what?
somites in a Cranio-caudal sequence
What is somite period?
- Day 20-30 (Somite Period): 38 pairs of somites, forming “axial skeleton” laid
- All done from paraxial mesoderm
day 20: first somite stage
What does lateral mesoderm make? Intermediate mesoderm?
Intermediate: gonads, kidneys
Lateral: cardiogram
Intraembryonic Coelom space fuses to form what?
What does it split?
form horseshoe-shaped cavity, intraembryonic coelom by splitting the lateral mesoderm
What does the lateral mesoderm split into?
Early development of cardiovascular system?
Vasculogensis and angiogensis?
The heart & great vessels originate from what?
cardiogenic mesoderm (derived from lateral plate mesoderm) present at the cranial most region.
Lacunae in the lateral mesoderm contribute to the formation of what?
pericardial coelom (which gives rise to the pericardium).
Paired, endothelial-lined endocardial heart tubes fuse & form what?
form a primordial heart tube from the splanchnic mesoderm adjacent to the endoderm and the chorionic sac (yolk sac)
2nd chorionic villus and tertiary?
How do you form a a functional cardiovascular system having
3 branches by day 26
The heart tube joins with blood vessels in the embryo, connecting the stalk, chorion, and umbilical vesicle
What are the 3 branches of functional cardiovascular system?
look at page 38
What does week 4 begin?
organogenetic - 4-8 weeks all the organs are formed
What s the most critical and senstive period?
4th week
Human development in utero occurs in three phases that are interrelated:
What does the folding of embryo require?
Besides the folding of embryo, what are other important events during organogenetic phase?
- development of main organs: primordia of all tissues and organs formed
- Constriction at the embryo-umbilical vesicle junction-> 2nd yolk sac undergoes constriction
Folding of the flat trilaminar embryonic disc converts the embryo into what?
cylinder, defining major external & internal embryonic structures.
Til lDay21embryo is straight with4-12 somites and begins to fold by day _
22
Cranially,the neural folds form what?
brain primordium projecting dorsally & later folding ventrally by end of D22
the neural crest cells starts moving where
intra-embryonic mesoderm and the primordium of the brain is formed dorso-cranially, but is bent/folded ventrally
Ventral inversion:
Primordial heart, Pericardial coelom + septum transversum
As the heart moves, endodermal region forms what?
septum transverum-> will move with heart and give rise to diagram
The septum transversum ,primordial heart, pericardial coelom, and oropharyngeal membrane begins to do what?
Positional inversion and fold vertally
Till Day21 septum transversum lies how?
cranially to the heart, & is not inverted
What does the septum transverum give rise to?
future diaphragm, thus partitioning the abdominal cavities and thoracic cavities. (separates out the lungs and heart from visera)
- How does the forebrain inverts?
- What does the folding bring?
- ventrally
- Folding brings umbilical vesicle endoderm to form the foregury (primodium of pharynx, esophagus, and lower respiratory system) which lies between the forebrain and primordial heart
- The Stomodeum emerges due to this folding.
Why is the heart moving?
amnion is decending down and pinching
rapid growth of the caudal neural tube forms what? What does it consist of?
rapid growth of the caudal neural tube forms the tail fold, consisting of spinal cord primordium.
caudal eminence projects over what? What does this form?
caudal eminence projects over the cloacal membrane, forming the future anus.
Between D22-26, the rapid growth of spinal cord, causes what?
inverts the allantois (a sac like structure), connects the fetal bladder to the yolk sac and removes nitrogenous wast via umbical sac vasculature
What fuses together to make umbilical cord?
Connecting stalk and umbilical vesicle
Cranially, the forebrain develops how?
beyond the stomodeum and overhangs the developing heart
How is the omphaloenteric duct formed?
Constriction at the embryo-umbilical vesicle junction becomes prominent & a Omphaloenteric duct is formed
Why do we have heart in right place
axial folding
What is the Omphaloenteric duct
- connection between midgut and umbilical vesicle
- Will stay so when intesting grows, it has a space until the body grows more
Later, a constriction in the Omphaloenteric duct defines the formation of what?
Umbilical cord
What does the nerual crest cells form?
Neural Crest cells have now formed well defined spinal ganglia flanking the neural tube.
What surround the midgut?
dorsal mesentery
Horizontal folding (rolling across the width) of the embryo produces what?
right and left lateral folds
ventrolateral abdominal wall fold towards what? What does this cause?
ventrolateral abdominal wall fold toward the median plane, converting the disc-shaped embryo->into a cylindrical embryo.
spinal cord broadens and what grows?
somites grow laterally
For the cylindrical human embryo, the Folding takes place in two directions, what are they?
Longitudinal (cephalo-caudal) folding is due to rapid enlargement of the cranial end of the neural tube & the form of the primordial brain
Lateral or transverse: Lateral folding is a consequence of the rapid enlargement of the somites. The process of lateral folding brings the amnioblast down to wrap around the embryo, pinching the yolk sac & forming the body wall
What forms the body wall?
Somatopleure
Lateral folding fuses 3 germ layers on the left & right to fuse & form what?
a cylinder
the endoderm in the center forms what?
midgut; a primordium of the small intestine
the foregut & hindgut are already defined.
- Lateral folding squeezes what?
- What is the result of this?
Lateral folding squeezes the yolk sac & reduces the connection between midgut & umbilical vesicle (yolk sac), forming an Omphaloenteric duct
What does the ectoderm, mesoderm and endoderm give rise to?
Major morphological changes in the embryo occurs during what week?
4th week
What are the Morphological changes in the Early Fourth Week (Day 22-23)
- Day22: (4th week) the embryo is straight with ~4-10 somites.
- Day23: The medially placed neural tube has 8-10 somites, & neural tube is open to the amniotic cavity at the cranial and caudal ends through the rostral and caudal neuropores.
Do we need the rostral and caudal neuropore open or closed
need to close it or the amnionic fluid will come in -> damage spinal cord and cause spinal bifida
When does the 1st pharyngeal arch form and the pumping of the heart
day 24
What does the first pharyngeal arches form?
pair of pharyngeal arches (mandibular arch) emerge, which will later form the mandible (lower jaw) & maxilla (upper jaw).
What does the embryo continue to do?
continues to fold, showing ~13 somites
What happens to the heart on day 24?
The heart starts pumping blood (rhymmical) ; seen at the heart prominence
rostral neuropore or caudal neruopore close first?
rostral neuropore closes; caudal neuropore remains open for longer period of time.
Upper limb buds develop as what?
small swellings on the ventrolateral body.
As the Lower limb buds emerges, what closes and emerges?
caudal neuropore closes
& nasal placode prominently emerges.
Primordial organ systems form:
large primordial heart defines atrium & ventricular prominences
Why are the limbs lower in the embryo?
becasue the head is growing more
In late fourth week, what happens?
- Three pairs of pharyngeal arches emerge at 27-somite stage.
- Rostral neuropore closes, the fore brain enlarges and embryo is C-shaped.
- The lens placode (for the eye) and the otic pit (future internal ear) & the nasal placode develop
- The neural fold fuses to form what?
- What does neural tube does?
Neural fold fuses to form the neural tube
the neural tube delaminates from the ectoderm
