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embryology > week 3 and gastrulation > Flashcards

week 3 and gastrulation Flashcards

1
Q

process of gastrulation

A
  • becoming trilaminar: ectoderm, endoderm, mesoderm
  • new structures: primitive streak, notochord, neural tube, somites
  • definition of body axes: spatial coordination of cell fates
  • ends with the formation of tail bud
  • endoblast enduces ectoblast to form mesoderm
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2
Q

primitive streak

A
  • dorsal view
  • cranial end is expanded in primitive node
  • thickened linear band appearing caudally in the median plane of the dorsal surface of the embryonic disc
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3
Q

shape

A

bilaminar developing embryo becomes oval

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4
Q

impact of primitive streak on body axes

A
  • defines 2 major body axes
  • cranial-caudal axis
  • medial-lateral axis
  • cell of anterior and posterior portions of embryo start expressing different genes
  • oropharyngeal membrane
  • cloacal membrane
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5
Q

definition of start expressing different genes

A
  • expression of nodal and Wnt becomes restricted to the caudal region by factors produced by anterior visceral endoderm (AVE)
  • AVE: a specialised cranial endoderm area
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6
Q

primitive streak formation

A
  • heralds the beginning of gastrulation
  • elongates and occupies half length of embryonic disc
  • primitive groove becomes deeper
  • cranial end expanded into primitive node containing depression: primitive pit continuous with groove
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7
Q

genetic regulation of laterality: nodal flow model

A
  • each cell of the node contains a single cilium: mono-cilium
  • mono-cilia of central cells are motile: rotate in vortical fashion and generate leftward flow of fluid
  • morphogen hypothesis: clockwise beating transports NVPs towards left side of node
  • two-cilia hypothesis: fluid flow generated is sense by immotile cilia on peridonal cells by mechanical stimulus
  • the nodal flow is a conserved symmetry-breaking event
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8
Q

molecular basis of primitive streak and groove formation

A
  • epithelial-mesenchymal transition (EMT): allows polarised adherent epithelial cell to assume a mesenchymal cell phenotype which includes enhanced migratory capacity, invasiveness, elevated resistance to apoptosis, increased production of ECM components
  • this causes formation of mesenchymal cells that migrate away from the epithelial layer in which it originated
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9
Q

formation of 3 germ layer

A
  • epiblastic cells displace hypoblast cells to form endoderm
  • epiblastic cells form mesoderm between epi and hypo: cells migrate through streak/node entering at different moments trough streak: tissue origin and timing of invagination affect the destiniy of tissues
  • cell remaining in epiblast from the ectoderm
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10
Q

primitive node and streak are an organiser

A
  • primitive node induces other tissues
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11
Q

fate of epiblastic cells

A
  • timing, origin and jump site
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12
Q

paths of migration of mesoderm in gastrulation

A

migrating
- caudailly: mesoderm lying on either side of midline
- cranially: cardiogenic mesoderm
- laterally: paraxial, intermediate and lateral plate mesoderm

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13
Q

the notochord

A
  • aka axial mesoderm, notochordal process
  • defining structure forming all chordate embryos
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14
Q

functions of notochord

A
  1. provides support for embryo
  2. it induces the differentiation of neuro-ectoderm
  3. contributes to the development of paraxial mesoderm
  4. it determines the longtudinal axis of the embryo
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15
Q

formation of the notochord

A
  • through the addition of cells to its caudal end at the primitive streak regresses
  • true cranial growth of notochord is minimal
  • involves shaping
  • multiple steps:
    1. canalization,intercalation, excalation
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16
Q

notochord in adult life

A
  • during later development the rudiments of vertebral bodies coalesce around the notochord
  • notochord forms nucleus pulposus at centre of vertebral discs
  • early childhood cells of notochordal origin degenerate and are replaced by adjacent mesodermal cells
17
Q

differentiation of mesoderm on either side of midline

A
  • lateral plate: splanchnic (circ), somatic (body cavity), extra-embryonic
  • intermediate: kidney, gonads
  • paraxial mesoderm: head, somite: sclerotome,myotome,dermatome
  • coelom
18
Q

forming paraxial mesoderm

A
  • mesoderm that begins the ingression through the middle part of primitive streak gives rise to paraxial mesoderm which immediately flanks the notochord
  • this mesoderm forms the somites: will provide segmentation along the cranio-caudal axis
  • in humans there are 42-44 pairs of somites - 5-7 most caudal degenrate
  • they will give rise to bones, connective tissue and skeletal muscles associated to the structures in each specific region
  • first pair forms day 20 at head-trunk border, then 3-4 per day
19
Q

paraxial mesoderm: head vs trunk

A
  • future head region: mesoderm forms band of cells that remain segmented: head mesoderm
  • later becomes head mesenchyme to which neural cells contribute later
  • will give rise to striated muscle of the face,jaw, throat
  • future trunk: the mesodermal bands of cells segment into somites, blocklike condensation of mesoderm
20
Q

determination of primordial CNS

A
  • notochordal process induces overlaying ectoderm to form neural plate
21
Q

forming the neural plate

A
  • day 18: first event
  • neural plate develops just cranially the primitive node in the ectoderm
  • primitive streak: organiser
  • day 19-20: ectodermal cells differentiate into a thick plate of pseudo-stratified columnar neuroepithelial cells
  • neural plate is broad cranially: future brain
  • tapered caudally: future spinal cord
22
Q

ectoderm derivatives

A
  • skin
  • CNS
  • PNS
  • eyes
  • internal ear
  • neural crest cells
  • bones and connective tissue of face and some skull
23
Q

mesoderm derivatives

A
  • connective tissue
  • muscles
  • bones
  • urogenital system
  • cardiovascular system
24
Q

endoderm derivatives

A
  • gut
  • gut derivatives: liver, pancreas, lungs etc.
25
Q

tail bud/ caudal eminence

A
  • by day 20 remnants of primitive streak swell to produce a caudal midline mass of mesoderm
  • will form most caudal structures
  • the tail bud provides a cell reservoir for caudal extension of the embryo
26
Q

primary body development

A

formation of the three layers which assemble into organ rudiments

27
Q

secondary body development

A

end of gastrulation with formation of rudimental tail

28
Q

vertebrate tail

A
  • an extension of the main body axis caudal to the anus
  • follows a distinct developmental programme
29
Q

carnegie stages of human development

A
  • being based on the developmental structure
  • provide a universal system for comparing the embryonic development of vertebrates

embryology (9 decks)

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