Early fetal development Flashcards
how is gestational age calculated
beginning of last menstrual period
Carnegie stage:
23 stages of embryo development based on embryo features not time
Allows comparison of developmental rates between species
Covers the window of 0-60 days fertilization age in humans
fertilization age
also known as conceptual age):
measured from the time of fertilization (assumed to be +1 day from last ovulation)
difficult to know time of fertilization exactly (unless IVF)
how long does the embryonic stage last?
16-50 days
Establishment of the germ layers and differentiation of tissue types
Establishment of the body plan
fetal stage
after 50 days
8-38 weeks
organ systems present
migartion of organ systems to final location
embryogenic stage
14-16 days Determining two populations of cells: pluripotent embryonic cells (contribute to fetus) Extraembryonic cells (contribute to the support structures eg placenta)
first few days of life
-Ovulated oocyte (1 cell) - Zygote - cleavage stage embryos (2-8 cells) - Morula 16+cells - blastocyst 200-300 cells
when is zona pelucida formed?
surrounds the ovulated oocyte so from very beginning
zygotic genome activation
happens when?
4-8 cell stage
transcription of embryonic genes so embryo is no longer dependant on maternal mRNAs and proteins
- now genes of embryo can be transcribed
Compaction
stage when outer cells begin to press against zona pelucida
how does ovulated oocyte become morula > blastocyst
1- compacted morula with outer cells pressed agaibst zona pelucida
2- inner and outer cells reorganize
= blastocoel cavity is formed
outline what are the effects of outer cells becoming pressed against zona pelucida?
COMPACTION
Change from spherical to wedge-shaped.
Outer cells connect to each other through tight gap junctions and desmosomes
Forms barrier to diffusion between inner and outer embryo
Outer cells become polarised
blastocoel
fluid filled cavity formed
osmotically by
trophoblast pumping
Na+ ions into cavity
zona pellucida
Hard protein shell inhibiting polyspermy and protects early embryo
Inner cell mass
Pluripotent embryonic cells that will contribute to the final organism
which cell contribute to the extraembryonic structures
Trophoectoderm
to implant what must the blastocyst do ?
how ?
escape zona pellucida
by contraction and digestion
formation of syncitiotrophoblast
trophoblast cells fuse to form
syncitiotrophoblast
function
destroys local uterine endometrium cells, syncitiotrophoblast cells invade
- interface between maternal blood and embryo formed
what are cytotrophoblast cells
from trophoectoderm
cells remain individual to provide source of syncitiotrophoblast cells
how do inner cells divide?
epiblast
hypoblast
final stage before gastrulation?
bilaminar embryonic disc
amnionic cavity forms ; creating 2 cavities
This leaves a two-layer disc of epiblast and hypoblast, sandwiched between cavities.
amnion, amniotic cavity, ___,hypoblast,____
amnion, amniotic cavity, epiblast, hypoblast, blastocoel, Cytotrophoblast
amnion, _____ , _____, hypoblast, _____, Cytotrophoblast
amnion, amniotic cavity, epiblast, hypoblast, blastocoel, Cytotrophoblast
draw out embryonic cell lineages complete
zona pelucida> inner cell mass and the outer cells > trophoblast
inner cell: epiblast and hypoblast
trophoblast > syncitiotrophoblast, cytotrophoblast
epiblast split into amnion and epiblast by formation of amniotic cavity
epiblast > ectoderm, mesoderm, endoderm
endoderm - which organs
GI tract, liver, pancreas, lung, thyroid
ectoderm- organs
CNS , neural crest
skin epithelia
tooth enamel
mesoderm
blood muscle gonads kidneys, adrenal cortex bone , cartilage heart
notochord
is a rod-like tube structure formed of cartilage-like cells
Forms along the embryo midline, under the ectoderm
Acts as a key organizing centre for neurulation and mesoderm development
neurulation
notochord signalling creates neural groove
= creates two ridges : neural folds
> move towards each other over neural groove
= forms hollow tube
neural tube overlaid with epidermis - ectoderm derived
failure of neural tube closure causes which conditions?
spina bifida
anencephaly
outline somitogenesis
either side of neural tube
paired blocks of paraxial mesoderm
symmetrical blocks bud off in pairs
= somites
commences at head end and progresses down the long axis of the embryo
how many pairs of somites do humans have?
42-44
somite initial two types of tissue?
dermomyotome
sclerotome
what is the vertebrae and rib cartilage derived from?
sclerotome
dermomyotome
dermatome
myotome
dermatome
gives rise to dermis of the skin, some fat and connective tissues of neck and trunk
mytome
forms the muscles of the embryo
what arises from two types of folding in the embryo:
and what type of folding is this?
primitive gut
Ventral folding: where the head and tail ends curl together
Lateral folding: where the two sides of the embryo roll
this folding pinches of the yolk sac = forming primitive gut
when is the fetal heartbeat detectable?
Fetal heartbeat detectable from ~6 weeks gestational age
