embryo 1 (wk8) Flashcards
what type of cell do we start off as
totipotent cell
fetus vs newborn
- Fetus - an organism that breathes no air, does not use the
digestive tract and lives in a sterile environment - Newborn - an air-breathing organism with a functional GI tract that quickly becomes colonized by microbial flora
what is produced in the ovaries
oocytes (female haploid gametes)
estrogen and progesterone
what happens in the uterine tube (fallopian tube)
§ Receives oocyte from ovaries
§ Site where sperm fertilizes the oocyte
where does the embryo develop
its also the same place where the placenta and membrane develop
uterus
placenta
site where the maternal and embryonic vasculature exchange substances
what is meosis
diploid (germ cell) –> haploid gamete
meiosis
§ A diploid cell (germ cell) undergoes meiosis to produce a
unique haploid gamete
- Unique–>crossing-over between maternal and paternal chromatids during prophase I to end up with “mixed” chromatids
- “mixed” = some paternal, some maternal genes
what is needed to complete meiosis
sperm
- Meiosis is not completed in an oocyte until the sperm penetrates
the oocyte
§ Spermatic pronucleus and the oocyte pronucleus fuse, thus completing fertilization
how is fertilization completed
- Combination of spermatic and oocyte genetic material–>diploid cell
zygote
single diploid cell
combine sperm and oocyte
simple meiosis
meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes. In humans, the haploid cells made in meiosis are sperm and eggs.
prepuberty in ovaries
stop at meiosis I
- A person with ovaries is born with a certain number of diploid oocytes that have been “paused” during the first stage of meiosis – do not continue meiosis until after puberty
post puberty in ovaries
fertilize vs non fertilize
do meiosis II if fertilized
- After puberty, the ovaries release an ovum each cycle into the uterine tubes
§ The oocyte will not complete meiosis II unless fertilization occurs
§ Fertilization typically occurs in the ampulla of the uterine tube
where does fertilization occur
in the ampulla of the uterine tube
what is ovulation
release of a secondary oocyte from ovarian follicle
what is cumulus oophorus
Ovulated secondary oocyte together with zona pellucida, is externally covered with granulosa cells – cumulus oophorus
how is corona radiata formed?
Cumulus oophorus will rearrange and form corona radiata
where does the sperm cell penetrate into>
zona pellucida
- Sperm cell penetrates the zona pellucida and “injects” its genetic material into the oocyte
§ Afterwards, the zona pellucida becomes impenetrable to other sperm cells (can’t have “double fertilization”)
how long for meiosis II to occur when sperm enters oocyte
§ After approximately 24 hours, the oocyte completes meiosis II and the zygote completes the first cell division
* This is the end of day 1, week 1
what is the corona radiata
cells that surround the oocyte, found outside of the zona pellucida
how do sperm get into the oocyte
- attracted to corona radiata and then break barrier to get to zone pellucida
- when get to zone pellucid, trigger acrosome reaction. sperm secrete digestive enzymes to break down glycoprotein membrane of zone pellucid to get into plasma membrane
- get into plsama membrane and fuse with oocyte. sperm releases its nucleus into the cytoplasm of the oocyte
what are the 2 gametes
oocyte and sperm
gamete
- Gamete – a haploid germ cell
§ Oocyte – gamete from ovaries
§ Sperm – gamete from testes
fertilization
fusion of the pronucleus of the two gametes (oocyte and sperm)
zona pellucida
protein coat that surrounds an oocyte as well as the
early embryo
zygote
a fertilized, diploid oocyte – has not yet divided
embyro
– multicellular organism, prior to fetal stage
§ Arbitrarily defined as period from fertilization – end of week 7
fetus
(multicellular organism, from end of embryonic stage (wk 8) to birth
neonate
newbron
extraembroynic
cells formed during development that do not become part of the neonatal organism, but involute or contribute to the fetal membranes
embryo vs fetus week timeline
embryo; week 0-7
fetus; week 8-brith
blastocoel
fluid cavity
morula
approximately 16-cell stage (12 – 32 cells) of an embryo
§ No blastocoel
blastocyst
a spherical mass of cells that is composed of a trophoblast that surrounds a fluid cavity (blastocoel) and an inner cell mass (embryoblast)
blastocyst 2 parts
trophoblast and embryoblast
cleavage
cell division in the early embryo–> each division does not increase the size of the embryo, instead each division results in smaller and smaller cells
blastomere
a cell that is totipotential and is present during very early development (first week)
§ Product of cleavage
totipotential
a cell that can become any cell
implantation
occurs when an embryo contacts and then becomes surrounded by the endometrium of the uterus
what gets implanted in the uterine wall/ cavity
blastocyst (after it sheds zone pellucida)
what is the 3 main steps in week 1
- fertilization
- zygote –> blastocyst
- adhere to endometrium (uterus) for implantation
what is cell division AKA and what does it form
cleavage; blastomeres
what is the trophoblast develop into
Manyofthesecellsdevelopintothe membranes of placenta
what does the embryoblast develop into
these cells develop into the embryo
embryoblast vs trophoblast; which is inner layer and which is outer
embryoblast aka inner cell mass
trophoblast is outer layer; but still covered by zone pellucida
where does fertilization of the oocyte occur
ampulla of uterine tube
how does the blastocyst get to the fundus of the uterus from the ampulla of there uterine tube
from increased in progesterone after ovulation and from cilliary movement in “wave”
zona pellucida roles
barrier, communication, immunologic defense, signal
§ Barrier that ensures that only one sperm fertilizes an oocyte
§ Porous – allows communication between the embryo and the maternal reproductive structures
§ Protects the embryo from immunologic defences
§ Acts as a signal to help with differentiation of
trophoblast cells
§ Prevents premature implantation of the embryo
§ Prevents the blastomeres from dissociating
what does the zone pellucida help prevent
early implantation of the embryo which leads to ectopic pregnancy
when does embryo hatch out of zone pellucida
day 6
how does the zone pellucida get broken down so that the blastocyst can hatch through
§ The trophoblastic cells just over the embryoblast seem to secrete/produce particular proteinases that weaken the wall of the ZP
§ The blastocyst “hatches” through this defect in the ZP and is ready to contact the endometrium and implant itself within it
how does blastrocyst where to endometrial epithelium (2 parts)
endometrial epithelium has mucin and pinopods
trophoblast binds pinopods
adhesion via selectin (binds mucins) and integral binding
when trophoblast contacts endometrial epithelium which 2 layers are formed; and which is inner and outer
cytotrophoblast- inner layer
syncytiotrophoblast- outer layer
at which day does blastocyst contact endometrial epithelium
day 6
how blastocyst gets implanted
synctiotrophoblast becomes multinuclear cell and invades endometrial stroma
- Syncytiotrophoblast develops into a multinuclear cell “mass” where the borders between individual cells are indistinct
- The syncytiotrophoblast invades quickly and deeply into the endometrial stroma (area under the epithelial cell)
what happens when synctiotrophoblast invade endometrial stoma (2 functions)
- form villi via proteinases and adhesion molecules (later becomes placenta)
- secret human chorionic gonadotropin (hCG) to prevent shedding of endometrium
§ Invasion into the endometrial stroma and induction/formation of villi (later becomes the placenta)
* Proteinases and adhesion molecules perform this role §
Secretion of human chorionic gonadotropin (hCG)
* hCG prevents the shedding of the endometrium (and loss of the embryo) by maintaining ovarian secretion of steroid hormones (i.e. progesterone)
* hCG is the hormone detected in pregnancy tests
what 2 layers does the embryoblast divide into when synctiotrophoblast invades into the stroma
epiblast and hypoblast
§ Epiblast
* This layer will become embryo
proper
§ Hypoblast
* It will line the blastocystic cavity (coelom) and form the primary yolk sac
* Also known as the primary endoderm
what does epiblast becomes
embryo proper
what does hypoblast become
primary yolk sac
cephalad
towards the head region (anatomical term)
caudad
towards the “tail” region (anatomical term)
coelom
a fluid-filled cavity
gastrulation
the process of forming three embryonic germ layers; ectoderm, endoderm, mesoderm
ectoderm
outer
a layer that is typically found on the “exterior” of the organism
endoderm
inner
a layer that is typically found on the “interior” of the organism
mesoderm
middle
(intraembryonic mesoderm) – a layer found between the ectoderm and mesoderm
which 2 layers that are formed in gastrulation be formed in the later weeks and be extra embyronic
endoderm and mesoderm
endoderm and mesoderm can also be extra- embryonic (formation of extra-embryonic endoderm and mesoderm is not classified as gastrulation)
which day is implantation complete by and what does it look like
day 10
§ The embryo is completely embedded within the endometrium § Surrounded by syncytiotrophoblast cells
which cells undergo decidulatization and what do they become
stomal cells –> decidual cells
decidual cells purpose
get glycogen and lipids. contact syncytiotrophoblast= apoptosis and release nutrients needed for embryonic growth
- The stromal cells (below the epithelium) undergo decidualization
§ Now known as decidual cells
§ Decidual cells accumulate glycogen and lipids throughout the uterus
§ The decidual cells that the syncytiotrophoblast contact undergo apoptosis, releasing stored nutrients needed for embryonic growth (until the placenta is better established)
amnioblast
cells that surround the developing
amniotic cavity
what enlarges and gives rise to the amnioblast
epiblast
how is extra embryonic mesoderm formed
The hypoblast extends around the entire interior surface of the blastocoel
§ New class of cells begin to form and migrate between the hypoblast-derived cells (yolk sac or extraembryonic endoderm) and the cytotrophoblast. These cells form extraembryonic mesoderm
what does blastocoel turn into after hypoblast makes extra embryonic mesoderm
primary umbilical vesicle / primary yolk sac
what makes the bilmainar disk
hypoblast and epiblast
where does extra embryonic mesoderm develop
between the cytotrophoblast and the cells derived from the hypoblast
where is the extra embryonic coelom formed
between extra embryonic mesodermal cells
Fluid begins to accumulate between the extra- embryonic mesodermal cells to form another cavity that is known as the extraembryonic coelom
3 fluid filled cavities in week 2/3
- umbilical vesicles/ yolk sac
- amniotic cavity
- extra embryonic coelom
§ Umbilical vesicle – as the embryo develops the primary umbilical vesicle becomes the smaller secondary umbilical vesicle
§ The amniotic cavity – found above the epiblast
§ Extraembryonic coelom – as this enlarges and develops, it will develop into the chorionic cavity
what day does fluid in extra-embryonic mesoderm become extra-embryonic coelom
day 13
where is the extraembyronic coelom form
in extraembryonci mesoderm
Extraembryonic coelom completely surrounds the rest of the embryo everywhere except for at the junction of the amniotic cavity and the rest of the chorionic sac
the connecting stalk forms from what and will become what
derived from the extraembryonic mesoderm.
junction of the amniotic cavity and the rest of the chorionic sac
- This junction will become the connecting stalkàthis develops later into the umbilical cord
On day 13/14 what 2 layers are formed by the extraembyronic mesoderm
extra embryonic splanchnic mesoderm and extra embryonic somatic mesoderm
what separates the 2 layers of the extraembyronic mesoderm
fluid in the extraembryonic coelom
extra embryonic splanchnic mesoderm vs extra embryonic somatic mesoderm location
§ Extraembryonic splanchnic mesoderm – surrounds the umbilical vesicle(s) (yolk sac)
§ Extraembryonic somatic mesoderm – found just underneath the cytotrophoblast, inner lining of the chorionic sac
what is the chorion made of
extraembryonic somatic mesoderm + trophoblast
what is inside and outside of the chorionic sac
Chorionic sac encloses the embryo and its cavities, and is surrounded by the syncytiotrophoblast
when does extra embryonic coelom become chorionic cavity
day 14
how are the amniotic cavity, secondary umbilical vesicle, and bilaminar disk “attached” to the chorion
connecting stalk
What is formed when syncytiotrophoblast contact endometrial blood vessels
they deteriorate and blood pools = lacunar netowkrs
how is the embryo nourished
by oxygenated maternal blood via simple diffusion from lacunar networks and glycogen/ lipids from deteriorating decidual cells
-no circulation yet
how are primary villi formed and when
day13/14 cytotrophoblasts send extension to lacuna
precurors of functional placental villi
prechordal plate
§ Thickened area of columnar cells that acts as an organization
area, found in the cephalad region of the hypoblast
what are is prechordal plate at
cephlad region of hypoblast
role of prechordal plate
organizing center
induction
signaling “episodes” by key areas of the embryo that stimulate differentiation and development of local structures
what is the organizer for head and mouth region and induces formations of structures at cephalad pole
hypoblast
hypoblasts induce cephalad pole structure formation and what else do they do in conjunction with this
§ It also prevents the formation of structures that belong at the caudal aspect of the embryo
thickening of hypoblast forms
prechordal plate
main event in week 3
gastrulation
3 layers
* Ectoderm
* Mesoderm
* Endoderm
in week 3 what is the embryo now referred to as
gastrula
in week 3 what does the bilaminar embryonic disc become
trilaminar embryonic disc
when does gastrulation take place
week 3
when does the primitive streak appear
beginning of week 2
what is the primitive streak
thickened linear band in the median plane of the dorsal aspect of the embryonic disc
what region does the primitive streak initiate
caudal region of epiblast
how is the primitive streak formed
It results from proliferation and movement of epiblast cells
to the median plane of the embryonic disc
where does the primitive node form
Cells at the cephalad end of the primative streak proliferate to form a primitive node
where do the cells that form the mesenchyme come from
from deep surface of primitive streak
mesenchyme
embryonic connective tissue which forms the supporting tissues of the embryo (i.e. embryonic connective tissue)
what does some of the mesenchyme form
- Some mesenchyme forms mesoblastic cells (undifferentiated mesoderm)
§ The mesoblasts form the intraembryonic, or embryonic, mesoderm
where is embryonic mesoderm from (intraembryonic)
mesoblastic cells from mesenchyme
SIMPLE
ecto
endo
mesoderm
from what?
mesoderm from mesoblasts
endoderm from epiblast and primitive node/streak
ectoderm from remaining epiblast cells
what type of cells are mesenchymal cells? where do they migrate to? and what do they turn into>
pluripotent
Mesenchymal cells derived from the primitive streak migrate widely
differentiate to ie. Fibroblasts, chondroblasts, osteoblasts
embryonic endoderm in the roof of the umbilical vesicle is formed by?
Cells from the epiblast, as well as from the primitive node and other parts of the primitive streak, displace the hypoblast
embryonic ectoderm is formed by?
The cells remaining in the epiblastw
what gives rise to all 3 layers in gastrulation
epiblast
when does the primitive streak diminish in size and become insignificant structure in sacrococcugeal region
end of 4th week
