Aging&Development Flashcards
define fertilisation age
1 day after last ovulation
measured from time of fertilisation
define gestational age
calculated from the time of beginning of last menstrual period
what is Carnegie staging?
23 stages of embryo development
based on embryo features, not time
covers 0-60 day fertilisation age
when does the embryogenic stage occur?
14-16 days post fertilisation
what happens at the embryogenic stage?
the early embryo is differentiated from the fertilised oocyte
two populations of cells - pluripotent embryonic cells and extraembryonic cells
when does the embryonic stage occur?
16-50 days post fertilization
what defines the embryonic stage?
germ layers
differentiation of tissue types
body plan established
when does the fetal stage occur?
50-270 days post fertilization, i.e second and third trimester
what defines the fetal stage?
presence of major organs
migration of organs to final location
growth
acquisition of metal viability
name the stages from fertilised oocyte to the 200/300 cell structure
what is present at all stages?
1 cell zygote → cleavage stage embryos (2-8cells) → morula 16+ cells → blastocyst
zona pellucida
what is the maternal zygotic transition?
when does it happen?
embryo is dependent on maternal mRNA & proteins (made in oocyte development) until 4-8 cell stage
here embryogenic genes are transcripted (zygotic genome activation) → ↑ protein synthesis and organelle maturation
what is compaction? when does it occur?
outer cells of embryo are pressed against zone and become wedge shaped
outer cells connect via gap junctions and desmosomes → diffusion barrier between inner and outer embryo
outer cells are polarised
occurs after 8-cell stage
what happens to the blastocyst after compaction?
inner cells reorganise to one side to form the blastocoel cavity
what is the blastocoel? how is it formed?
fluid filled cavity
trophoblast pumps sodium ions into it and water osmotically follows
what are 2 functions of the zone pellucida?
prevents polyspermy
protects early embryo
what cells does the inner cell mass consist of?
pluripotent embryonic cells (contribute to final organism)
what is the trophoectoderm? what cells does it consist of?
outer cell layer - extra-embryonic cells i.e. trophoblasts (contribute to structures supporting development)
what is hatching? when and how does it occur?
when the embryo escapes the zone pellucida
at day 5-6
cellular contractions and enzymatic digestions
what happens in peri-implantation events?
@ day 7-9
trophoblasts → syncitiotrophoblasts & some cytotrophoblasts remain
inner cell mass → epiblast and hypoblast
what is the function of syncitiotrophoblasts and cytotrophoblasts?
destroy maternal endometrial cells to create interface between embryo and maternal blood supply
cytotrophoblasts remain to provide source of syncitiotrophoblasts
what do syncitiotrophoblasts secrete?
hcg - human chorionic gonadotrophin
what will the epiblast and hypoblast form?
epiblast → fetal tissues
hypoblast → yolk sac
what is the bilaminar embryonic disc formation? when does it occur?
day 12+
some epiblast cells become separated when the amniotic cavity is formed
cells above → amnion → extra-embryonic membranes
(picture from bottom to top : cytotrophoblast → blastocoel → hypoblast → epiblast → amniotic cavity → amnion → cytotrophoblasts dividing → syncitiotrophoblast → invading maternal endometrium)
what is gastrulation? when does it occur?
15 days post-fertilisation
1. primitive streak forms through epilblast → divides embryo into cranial and caudal ends (and L&R) with primitive pit in the centre and primitive groove towards caudal end
2. epiblast cells invaginate through streak and displace hypoblast cells
hypoblast cells → endoderm
epiblast cells → ectoderm
cells in between → mesoderm