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
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
3
Q
shape
A
bilaminar developing embryo becomes oval
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
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
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
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
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
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
10
Q
primitive node and streak are an organiser
A
- primitive node induces other tissues
11
Q
fate of epiblastic cells
A
- timing, origin and jump site
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
13
Q
the notochord
A
- aka axial mesoderm, notochordal process
- defining structure forming all chordate embryos
14
Q
functions of notochord
A
- provides support for embryo
- it induces the differentiation of neuro-ectoderm
- contributes to the development of paraxial mesoderm
- it determines the longtudinal axis of the embryo
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
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
