Lecture 8- Early embryology 1 Flashcards
how does one become a multicellular body?
- growth
- morphogenesis
- specialisation
morphogenesis
development of form and structure
from fertilisation to birth (3 stages)
pre-embryonic
embryonic
fetal
pre-embryonic
weeks 1-2
embryonic
3 to 9
foetal
9 to 38
pregnancy weeks is calculated from
date of last menstrual period
where does fertilisation take place
ampulla of the fallopian tubes
fertilised oocyte is called a
zygote
where is the ideal place for the embryo to implant
posterior uterine wall
pre-embryonic weeks (1-2) weeks involves
- cleavage
- compaction
- Implantation begins
cleavage occurs
within 30h of fetilisation (day 2)
what is cleavage
first mitts division resulting in two blastomeres of equal size
zona pellucida
forms around zygote and morula
morula formed when
32 cells within structure
cells in the morula are said to be
totipotent
totipotent
potential to become any cell
compaction
formation of first cavity in morula (blastocoel)
during compunction which structure is formed
blastocyst
before compaction all cells are
totipotent
after compact cell become
pluirpotent
pluripotent
capacity to become many cells
during blastocyst formation what happens
o Cell differentiation starts
- Trophoblasts- outer layer
- Inner cell mass- foetus
after compaction/ blastocyst formation the blastocyst
hatches (day 5) from zone pellucid
- can now enlarge and interact with uterine surface
when doe implantation begin
day 6-7
how many cells in conceptus at the beginning of implantation
around 100 cell
- of these 8 will make the embryo
- the rest will become fatal membrane
what happens to the outer cell mass in week2
outer cell mass differentiates into syncytiotrophoblast and cytotrophoblast
what happens to the inner cell mass
becomes bilaminar disk
- epiblast and hypoblast
epiblast
structure which the amniotic cavity grows from
hypoblast
cavity which the primitive yolk grows from
by the end of the 2nd week
conceptus has implanted
the embryo and its two cavities (amniotic and yolk sac) will be suspended by connecting stalk within a supporting sac (chorionic cavity)
chornionc cavity
support the conceptus
connecting stalk
connect the embryo to the uterine wall
syncytiotrophoblast
s the epithelial covering of the highly vascular embryonic placental villi, which invades the wall of the uterus to establish nutrient circulation between the embryo and the mother.
cytotrophblast
is the inner layer of the trophoblast. It is interior to the syncytiotrophoblast and external to the wall of the blastocyst in a developing embryo
chorionic villus
basic structural unit of metaneral- fetal exchange
- maternal blood flow within placenta (supports embryo)
primitive yolk sac membrane Is pushed away from cytotrophoblast layer by
an acellular extra embryonic reticulum
embryonic reticulum gets converted to
extraembyronic mesoderm by cell migration
by the end of week 2 the maternal sinusoids will have
invaded the synncytiotrophoblasts
- Lacunae become continuous with sinusoilds
when the lacunae become continuous with sinusoids
uteroplacenta circulation begins
near the end of week2 what forms
a secondary yolk sac
the secondary yolk sac is also called
the definitive yolk sac- pinches off from the primitive yolk sac
connecting stalk is the
future umbical cord
bleeding by the end of week 2 can be confused with
menstrual bleeding
50% of zygotes are
lost within the first 2-3 weeks
how many diagnosed pregnancies will miscarry
15%
how many women suffer recurrent miscarriagee
1%
aminiotic sac
Formed from spaces within the epiblast
blastocoele
first cavity- formed as a result of compaction
primitive yolk sac
exoelomic cavity
- formed by hypoblast lining blastocoele
secondary yolk sac
aka definitive yolk sac
- formed within primitive yolk sac
extraembryonic coelom
aka chronionic cavity
- formed from space within the extracembryonic reticulum and mesoderm
assisted reproductive technique
oocyte are fertilised in vitro and allowed to divide to the 4 or 9 cells take
what is transferred into the women uterus
the morula
benefits of assisted reproductive techniques
A cell can be safely removed from the morula and tested for conditions prior to transfer of the embryo into the mother
ectopic pregnancy
implantation at site other than uterine body
- peritoneal or ovarian
- life threatening emergency
Placenta praevia
implantation in inferior uterine segment
- can cause haemorrhage
- requires C-section