embryology week one & two Flashcards
embryology
study of origin and development of an individual
prenatal period
time between conception and birth
2 periods within prenatal period
embryonic and fetal period
embryonic period
first 8 weeks
fetal period
remaining 30 weeks
adult human body plan
skin, outer body wall (trunk), body cavities & inner tube
what happens in week 1?
fertilization & zygote formation, cleavage & blastocyst formation, beginning of implantation
how does the fertilization process begin?
with the release of an oocyte (immature egg) from the ovary uniting with a sperm
what happens when the sperm reaches the oocyte?
they bind to receptors on the zona pellucida around the oocyte
zona pellucida
external membrane around oocyte
zygote
chromosomes from the male & female gametes coming together within the ovum
cleavage
cell division, produces large number of cells that become building blocks of the embryo
blastomeres
zygote divides to create 2 daughter cells
morula
solid cluster of cells, 12-16 cells, that cleavage has created by day 3
compaction
tight alignment of morula cells allowing greater cell-to-cell interactions
blastocyst
tight cluster of cells with a cavity in the middle, cavity contains uterine fluid, will split into 2 groups
two distinct groups of blastocyst
trophoblast & embryoblast
trophoblast
outer cell layer surrounding the blastocyst cavity, helps from the placenta
embryoblast
inner cell mass, forms the embryo
how long does the blastocyst stage last?
3 days from days 4-7
what does the blastocyst do in those 3 days?
floats freely inside the uterine cavity where it will burrow into the uterine wall on day 6
implantation
begins on day 6 and takes one week to complete, time frame specific
what happens during the implantation time frame?
the trophoblast erodes the uterine lining units the entire blastocyst becomes embedded within the uterine wall
ectopic pregnancy
implantation does not attach on the wall of the uterus, very dangerous
when does week 2 begin?
day 9
day 9
inner cell mass has divided into two flat sheets of cells; epiblast & hypoblast
bilaminar embryonic disk
two layered disk made up from the epiblast and hypoblast, becomes precursor for entire body
amniotic sac
formed as an extension of the epiblast, amniotic fluid acts as cushion to protect embryo & fetus
yolk sac
formed as an extension of the hypoblast, gives rise to parts of the digestive tube and earliest blood vessels, nourishes embryo for short time
hCG hormone (human chorionic gonadotrophin)
produced in a layer of trophoblast at the end of implantation, basis for pregnancy tests
