Cleavage Flashcards
Cleavage =
one sentence definition
Rapid series of mitotic cell divisions which are inititated by the zygote within 24 hours after fertilisation
Impact of cleavage on the size of the embryo
& what is the name of the daughter cells
Size stays the same
Because divisions are not accompanied by cell growth
So the mitotic divisions simply divide the large zygote into many smaller daugther cells called BLASTOMERES
+ Bonus point = embryo remains enclosed in the zona pellucida
State the changes in the number of cell size in the first fve days after fertilisation of the egg cell and name any key names of what the mebryo is called at these stages
Day 0 = pronuclear stage
Day 1 = 2 cell
Day 2 = 4 cell
Day 3 = 8 cell
Day 4 = MORULA - 16 to 32 cells
Day 5 = BLASTOCYST
Fertilisation occurs in the ….. of the oviduct
Ampulla
During the first …. days the zygote undergoes …… as it travels down the ….. and enters the …..
On day … the …. hatches from the …. and is then able to implant into the uterine ….
5
cleavage
oviduct
uterus
5, blastocyst, zona pellucida, endometrium
….. causes some blastomeres to segregate to the centre of the morula and others to the outside.
Centrally places blastomeres are called ….
Blastomeres placed at the periphery = constitute the …..
COMPACTION
ICM = inner cell mass
Trophoblast
The inner cell mass gives rise to the ….. …. and is therefore also called the ….
embryo proper
embryoblast
Trophoblast = primary source of the fetal component of the …..
Placenta
Tranformation of Morula to Blastocyst
. What is the side of the embryo containing the ICM called
. And what is the opposite side called
- Embryonic pole
-Abembryonic pole
Explain the process which leads to the formation of blastoceol within the morula?
. The pumping of sodium into the interior of the morula through Na+/K+ ATPase
. Results in water moving in through osmosis to become BLASTOCOELIC FLUID
. As the hydrostatic pressure increases, a large cavity called the BLASTOCYST CAVITY (blastocoel) forms within the morula
As the trophblast differentiates, it assembles into an epithelium in which adjacent cells are tightly adherent to one another - this adhesion results from the deposition on lateral cell surfaces of ……. which is a ….. dependent cell-adhesion molecule and the formation of intracellular junctions such as 1,2,3 and 4
E-cadherin
Calcium
Tight junctions,
Gap junctions,
Adheren junctions
Desmosomes
The embryoblast cells (inner cell mass) then form a compact mass at one side of this cavity, and the trophoblast organizes into a thin, single-layered epithelium. The embryo is now called a…..
blastocyst
End of ……..: Initiating Implantation
Blastocyst Hatches From ……….Before Implanting
first week
zona pellucida
Before implanting the blastocyst hatches from the zona pellucida by using …. (basically to bore a hole in & to squeeze out)
enzymes
Implantation
. ….. is adherent, attaches to the uterine epithelium
Blastocyst
If an embryo implants, cells of the trophoblast produce the hormone ….. which supports the …. and thus maintains supply of ……. (maternal recognition of pregnancy)
hCG = human chorionic gonadotropin
corpus luteum
progesterone
The corpus luteum continues to secrete sex steroids for 11 to 12 weeks of embryonic development, after which the ….. itself begins to secrete large amounts of progesterone and the corpus luteum slowly involutes, becoming a corpus albicans.
(in the absence of an implanted embryo, the …… normally degnerates.
placenta
corpus luteum
What is the decidua?
It is the endometrium of the uterus in a pregnant woman - it is the functional layer of th endometrium that separates from the remainder of the uterus after childbirth
In response to the ……. …. levels in the maternal blood
Connective tissue cells of the decidua …… to form decidual cells
these cells enlarge as glycogen & lipid accuulate in their cytoplasm
increasing progesterone
enlarge
The cellular and vascular changes occurring in the endometrium as the blastocyst implants constitute the
Decidual reaction
Decidual reaction occurs and cells in endometrial stroma
- become more vascularised
- oedomatous (fluid filled)
- endometrial glands enlarge
Implantation at abnormal sites =
results in ectopic pregnancy
Clinical relevance of ectopic pregnancy
. Occurs when implantation occurs at an abnormal site like peritoneal cavity, fallopian tube, ovary
. Still results in decidual reaction so risk of vascular rupture increases
(because the epithelium at these abnormal sites still responds to the implanting blastocyst with increased vascularity & other supportive changes)
Symptoms & Treatment of Ectopic Pregnancies
- symptoms = abdominal pain, vaginal bleeding
- treatment - embryo will never reach term
usually surgical intervention is required to interrupt the pregnancy and prevent maternal death
Name the drug used for ectopic pregnancies
Methyltrexate - blocks rapid cell division
….. plug as the embryo becomes fully implanted
coagulation
Invasive trophoblastwithout distinct cell boundaries=…..
what does that produce and do? is this the outer or the inner layer?
Name of the other layer & is that outer or inner
syncytiotrophoblast, they producehCG(human chorionic gonadotropin) whichmaintains the corpus luteum
- Inner layer of mononuclear trophoblasts = cytotrophoblast
Development of the……. ….. disc
….. differentiates into two layers - ….. and ….
bilaminar germ
ICM
epiblast
hypoblast
