EMBRYOLOGY Flashcards
What does the ectoderm form?
Forms outer epithelium (skin)
Forms nervous system
What does the mesoderm become?
Musculoskeletal system, including smooth muscle
What does endoderm become?
Intestinal epithelium
What does mesoderm produce as it differentiates?
Embryonic mesenchyme
Term for loose tissue stuff that forms blood vessels, tendons, cartilage, muscles etc.
What are the 4 different tissue types in embryology and what are they formed form?
- Epithelium—> skin, lungs and GIT lining (ectoderm)
- Neural (ectoderm)
- Contractile, muscles —> (mesoderm)
- Connective —> everything not 1,2,3 (endoderm)
Where is most of the loose connective tissue formed during embryonic development and what are its features?
Umbilical cord
Hydrophilic ECM
Jelly like (Whartons jelly)
What are the 5 main stages in embryology?
Fertilisation
Early cell division
Formation of 3 fundamental cell type
Emergence of body plan
Post embryonic development
What is each cell in the morula called
Blastomere
At what point is it called a morula
16-32 cells
What is a blastocysts
Shell around exterior and inner cell mass has formed
What are the two parts of the inner cell mass called
Epiblast
Hypoblast
What is gastrulatiom
Process of cellular rearrangement which involved formation of tri- laminar disk
What is the first visible sign of gastrulatiom
Formation of primitive streak (midline groove at epiblast cells migrate caudal to cranial)
What is the primitive node
The end of the streak
How is endoderm formed
Epiblast cells migrate through the primitive pit and displace the hypoblast cells
How ks the mesoderm formed?
Epiblast cells migrate through the primitive pit and lie between the epiblast layer and the newly created endoderm
How is the ectoderm formed
By the Epiblast cells that remain in position
How is the notochordal process formed
Prenotochodral cells move into pit and cranially becoming notochordal process
Forms notochordal plate, allowing pressure equilibrium Plate fuses together to form notochord
How is neural tube for,ed
Notochordal has natural kinks (grooves) in it
Lateral edges form neural fold, which fuse together to form neural tube
Occurs cranially (brain) and causally (spinal chord_
How is the neural crest formed?
Neural tube has already formed
Some ectodermsl cells from tube migrate which forms neural crest
What does the neural crest form
Peripheral NS
What does the neural tube form?
Spinal cord
What are somites formed from and where are they?
Derived from para axial mesoderm (either side of neural tube)
Same amount each side of tube
Lateral to neural tube and notochord
How can you age mesoderm
By how many somites there are
What will somites form
Skeletal muscles
Tendons
Cartilage
What are somites important for
Segmentation
What’s are the three different parts of the somite?
Dermatome
Myotome
Sclerotome
What determines fate of multi potent cells within somites
Location within somite and factors from surrounding tissues
What generates the axial (vertebrae) skeleton
Somites
What generates the limb skeleton
Lateral plate mesoderm
What generates the skull and face
Neural crest and head mesoderm
How is the vertebrae developed?
Sclerotome cells are attracted to notochord and neural tube region
Sclerotome cells form vertebrae body
Develops from caudal part of one Sclerotome to cranial part of the next one
Sclerotome cells covering neural tube form neural arches which fuses which corresponding vertebrae body
What are the three different axes in ensuring limbs are laid out correctly
- proximal distal (shoulder- finger tip)
- antero- posterior (thumb- little finger)
- dorso- ventral (knuckle- palm)
How are limb buds formed?
Proliferation of skeletal and muscle precursors
Cells accumulate under the ectoderm creating a bulge (limb bud)
What is the AER
Apical ectoderm ridge (thickening of ectoderm at the tip of the limb bud)
Major signalling centre
Induced my mesenchyme cells
What is the progress zone?
Distal part of the mesenchyme extends the limb bud by proliferation
What helps coordinate the anterior posterior axis
Sonic hedgehog signalling molecule
Organised by a small block of the mesoderm called zone of polarising activity
How are digits formed
Via concentration gradient of sonic hedgehog molecule
Apoptosis
What controls the dorsal ventral axis
Ectoderm
Peels off and rotates the ectoderm relative to the mesenchyme
How are synovial joints formed?
- Pre cavitation —> mesenchyme converted into cartilage. Then chondral ossification occurs and and chondrocytes left over form articular cartilage
- Cavitation —> interzone between adjacent bones differentiate into dense connective tissue. Cells undergo apoptosis and hyaluronic acid synthesis
- Post cavitation—> hyaluronic acid causes tissue separation to create joint cavity
