Embryology Flashcards
define embryology
anatomical description diff stages development
morphogenesis
development internal + external form + structure
define developmental biology
embryology + mechanisms involved in regulation
2 cell types
- somatic - of body, limited life
- germ line - for repro, immortal
3 types mammals
- monotremes - lay eggs
- marsupials - short gestation, immature young
- placentals - more mature when born
marsupial embryos still have a placenta
key stages embryo development
- cleavage
- compaction
- formation trophectoderm + blastocyst
- primitive endoderm
- implantation
- visceral + parietal endoderm
- formation primordial germ cells + migration genital ridges
- gastrulation
cleavage
cell division w/o cell growth from 1 cell embryo to 8 cell embryo
cells called blastomeres
zygote
fertilised oocyte
compaction
blastomeres maximise cell-cell contact to form morula
requires cell adhesion mol e-cadherin (epithelial calcium dependent adhesion) expressed on surface
Oct4
transcr factor required cell pluripotency, preventing premature differentiation ESCs
formation trophectoderm
only cells outer surface have free apical surface = transcription factor YAP enters nucleus = higher expression levels Cdx2, inhibiting Oct4 = differentiate to form TE
before all cells had Cdx2 + Oct4
formation blastocyst
TE pumps Na+ inside morula = water in by osmosis = fluid-filled cavity (blastocoel) forms
transcription factor
prot typically found nucleus responsible for turning genes on/off - which ones to mRNA to prots
functions trophectoderm
- pump Na+ into morula to form blastocyst - need Cdx2 to localise channels or not enough Na+ in
- hatching from zona pellucida
- implantation - helps digest through lining endometrium
- maintenance pregnancy
- formation placenta
cell polarisation meaning
intrinsic cell asymmetry - diff types prots diff parts cell
e.g. TE polarised apical-basal axis w 2 diff cell types slight diff prot expression = Na+ channels only on apical surface
blastocyst escapes ZP
- blastocoel expands until embryo pressing against ZP
- mural TE secretes strypsin - lyses hole in ZP
what happens to mural + polar TE after blastocyst escapes ZP
mural -> giant trophoblastic cells
* terminally diffed, non-invasive
polar -> proliferative cytotrophoblastic cells
* outside wall blastocyst + responsible implantation
formation primitive endoderm (=hypoblast)
fibroblast growth factors (FGF) in external environ bind receptors = activated + cytoplasmic part phosphorylated = signalling cascade = genes expressed for transcr factor Gata6
–> suppresses expression Oct4 = differentiate
–>turns genes on make basement mem
functions hypoblast
- deposit basement mem (for compartmentalisation)
- give rise extra-embryonic tissues to support growth
- secrete signalling mols
what are epiblast cells when out of embryo
embryonic stem cells
implantation
blastocyst-uterus adhesion
- initial low-strength interactions bet TE + endometrial epithelial cells
- then stronger contact made by cadherins on surfaces
- TE starts embedding uterus wall
receptivity uterus endometrium
undergoes cyclical changes + only receptive implantation in small window
* acheived by oestrogen + progesterone - level maintained chorionic gonadotropin (CG)
primitive endoderm -> parietal
- TE secretes parathyroid hormone-related peptide (PTHrP), causing diff
- no close connection neighbours so migrate + form layer underlying TE
- loads RER secrete loads ECM prots form thick basement mem (Reichert’s)
primitive endoderm -> visceral
- epiblast cells secrete bone morphogenic prots (BMPs), causing diff
- tall epithelial w microvilli + close connections to make epithelium
- support growth embryo - provide nutrients b4 placenta formed