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
tail bud/ caudal eminence
- 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
primary body development
formation of the three layers which assemble into organ rudiments
27
secondary body development
end of gastrulation with formation of rudimental tail
28
vertebrate tail
- an extension of the main body axis caudal to the anus
- follows a distinct developmental programme
29
carnegie stages of human development
- being based on the developmental structure
- provide a universal system for comparing the embryonic development of vertebrates
