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55 Cards in this Set

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main events of first two weeks
transport to implant site, development of bilaminar embryo, amniotic cavity & embryonic disc, implantation
2 events of first week following fertilization?
embryo transport from ampulla fertilization site to uterine implantation site, and blastula development.
blastula cells are what?
blastomeres – these are totipotential: each capable of producing complete organism
embryo movement down uterine tube why?
smooth muscle in the muscularis of the uterine tube, and beat of cilia on epithelial lining of tube.
why is there no net growth in size of the embryo during tubal transit
keeping embryo within zona pellucida for fertilization, not allowing ectopic implantation by preventing contact between trophoblast and epithelial lining of the tube.
what occurs during the 2nd week following fertilization?
embryo implants in the lining of the uterus and the amniotic cavity and primitive yolk sac are formed.
what is cleavage?
rapid mitotic divisions resulting in larger numbers of progressively smaller cells
when does the first cleavage division occur?
abt. 24 hrs after production of 2nd polar body
when do other divisions occur?
asynchronous at intervals 12 – 24 hrs.
potentiality of blastomeres as development proceeds?
becomes progressively restricted.
what occurs at the eight cell stage?
compaction (between the 3rd & 4th cleavage divisions)
what does this mean?
blastomeres maximize contact with each other, creating a tightly-packed ball of cells
tightly packed ball of cells called what?
morula
significance of morula stage
blastomeres no longer totipotent – can’t remove one without damaging others – too tightly packed.
what occurs during subsequent cleavages of the morula?
blastomeres become arranged either on the inside or the outside of the morula – this is the first sign of differentiation.
outer cells of morula are what, and do what?
trophoblast – seal the interior of the morula in.
does the trophoblast make a contribution to the embryo
NO.
trophoblast responsible for what?
implantation, and formation of the placenta
inner cells of morula called what, forms what?
inner cell mass, which forms the embryo.
4 days after fertilization, morula is where?
has arrived at the uterus at about the 32 cell stage. Fluid filled cavity (blastocyst cavity) appears, displacing cells of inner cell mass to one pole. (embryo is still within the zona pellucida)
appears in morula at 4th day?
cavity – water is taken on, displacing inner cell mass to one pole
what does morula become when cavity has appeared
blastocyst (still within zona pellucida)
Does blastocyst still have zona pellucida?
yes.
occurs with trophoblast about 5 days after fertilization?
trophoblast produces enzymes - disrupt zona pellucida
when the zona pellucida is distrupted?
embryo breaks out from zona.
name for embryo breaking out from zona
hatching
after hatching has taken place?
trophoblast can make contact with endometrium.
endometrium definition?
lining of uterus, contains epithelium, connective tissue to receive embryo during implantation, are shed during parturition/menstruation.
contact method: trophoblast with endometrium?
has tissues that bind with the surface of the uterus.
what forms at site of contact of trophoblast & endometrium, and how is it formed?
syncytiotrophoblast – trophoblast daughter cells proliferate, but fuse together in multinucleated mass
following the formation of the syncytiotrophoblast, what is the trophoblast called?
cytotrophoblast (to distinguish it from syncytiotrophoblast)
what occurs within the cytotrophoblast as the syncytiotrophoblast is forming?
cytotrophoblast cells are flattening within the blastocyst cavity, a layer next to the cavity is formed, called the hypoblast.
properties of the syncytiotrophoblast?
multinucleated, invasive, burrows into uterine lining, drags the embryo into the uterine lining behind it, produces hCG.
What is hCG?
Human Chorionic Gonadotropin: essential hormone for pregnancy: maintains proliferation of corpus luteum, secretes hormones - keeps uterine lining:receptive state
hormone that is basis for pregnancy test?
HCG - Human Chorionic Gonadotropin
other key role does the syncytiotrophoblast play in maintenance of pregnancy?
thought to play a role in keeping maternal immune system from rejecting the embryo as foreign tissue.
what is an ectopic pregnancy and why does it occur?
implantation in a place other than the body of the uterus – occurs because the trophoblast will implant anywhere convenient – can occur if egg is delayed
Approx. what % of pregnancies are ectopic?
1 in 100
what % of ectopic pregnancies are tubal?
more than 90%
why are tubal pregnancies a problem?
uterine tube unable to enlarge sufficiently to accommodate rapidly growing embryo – will rupture: risks life-threatening hemmorhage
what are other factors effecting tubal pregnancy
scar tissue or abnormalities (congenital or acquired) in the uterine tube as a result of infection – these delay the passage of the embryo such that zona comes off while embryo still in the tube.
what are other locations of ectopic pregnancies?
peritoneal or abdominal. (These can come to term, however must be delivered by cesarian.)
If a woman presents with vaginal bleeding, what should she be treated as?
pregnant until proven not pregnant (with tubal pregnancy and hemmorhage).
correct or normal implantation site?
upper wall of the uterus.
problem with tubal infection?
increased risk of tubal pregnancy
two possible treatments for tubal pregnancies?
salpingotomy: making hole in tube – extracting embryo from tube (problem as some embryo may be left behind, necessitating re-operation) may also create scarring rendering tube useless.salpingectomy – removal of tube.
what happens to the inner cell mass during the process of implantation?
becomes a two layered structure called the bilaminar embryonic disc – hypoblast is formed facing the blastocyst cavity. cavities forming in the inner cell massà coalesce à form amniotic cavity: floor of this cavity formed by single layer of cells: epiblast.
epiblast becomes?
embryo
what does the hypoblast become?
hypoblast cells multiply and spread, grow together to create a sac called the primitive yolk sac (within the cytotrophoblast
Does hypoblast contribute to fetus?
No. Is replaced by endoderm during gastrulation
what is the bilaminar embryonic disc and what is its context within the rest of the embryo?
disc= epiblast + hypoblast, sandwiched between two balloons: amniotic cavity + primitive yolk sac.
where is the primitive yolk sac?
within the cytotrophoblast
what % of pregancies are thought to spontaneously abort?
50 – 70% (woman wouldn’t know she was pregnant).
why do spontaneous abortions go unrecognized by mothers?
because they are during the first two weeks (woman simply thinks her period is late)
why do embryos spontaneously abort?
chromosomal abnormalities, implantation failure, maternal immune response, embryotoxic environmental agents such as heat, X-ray, ionizing radiation etc.