SFP: embryology week one Flashcards
what are corona radiata cells?
cells packed around the exterior of the egg
what is the zona pellucida?
the region directly deep to the corona radiata in an egg
name the three major steps required in fertilization
capacitation, acrosome reaction, zona reaction
describe capacitation
prepares the acrosome to release enzymes that break down the zona. the glycoprotein coat and seminal plasma proteins are removed from the membrane fo the sperm
describe the acrosome reaction
after the sperm contacts the zona pellucida, proliferations in the acrosomal wall result in the release of enzyme to allow penetration of the zona pellucida
describe the zona reaction
prevents polyspermia; the properties of the zona pellucida change to make it impermeable to other sperm
what sperm receptor is used to connect to the egg?
ZP3
acrosome reaction is a ___ dependent event
calcium
what is an important enzyme released prior to the acrosome reaction? what important enzyme is released during the acrosome reaction?
hyaluronidase: prior to acrosome reaction. dissolves the intercellular material between corona radiata cells
acrosin: during acrosome reaction. facilitates penetration of the zona by the sperm head
describe the zona reaction
binding of sperm fertilin a/b with egg integrins and CD9on the egg plasma membrane with oocyte plasma membrane triggers the zona reaction. this changes the ZP3 protein on the membrane to prevent polyspermy.
describe the developing features of the zygote during week one
compaction: increase in cell number but decrease in size
blastocyst: inner and outer cell masses with a cavity called the clastoceole
inner cell mass: embryoblast and stem cells
outer cell mass: trophoblast
when is the zygote ready for implantation?
at the end of week one when the zona pellucida degenerates
describe dizygotic twins
two egg, two sperm. they can develop completely separately or can have a fused placenta.
describe monozygotic twins
one egg, one sperm. the way the develop depends on how the blastocyst spits. if the inner mass splits far enough aparpt, the twins develop separately. if the inner mass splits but not completely, there can be a common amniotic cavity
does a fused placenta cause issues?
typically no
if the ___ doesn’t split far enough apart, it can cause conjoined twins
inner cell mass
name the different types of development in relation to placenta and amniotic cavity with monozygotic twins
dichorionic: two placentas
monochorionic: one placenta
diamniotic: two different amnions
monoamnionic: one amnion
describe the forms of trophoblasts
syncytiotrophoblast: the cells are connected and cell walls have faded. these invade the endometrial stroma
cytotrophoblast: still have their cell walls and are separate cells
in week two, the inner mass cells form….? describe their positions.
a hypoblast and an epiblast. the hypoblast is closest to the chorionic cavity/primitive yolk sac, and the epiblast is closest to the amniotic cavity.
which trophoblast type eventually becomes part of the placenta?
cytotrophoblasts
what are primary chorionic villi
peaks in the cytotrophoblasts that will eventually form the placenta
what are secondary villi
a mesenchyme core that forms directly deep to the primary villi
what causes ectopic pregnancy?
something impacting the fertilized egg making it to the uterus in proper time. if the zona pellucida disappears too soon, the egg could implant in the uterine tube on the way to the egg. infection could impact the speed at which the egg is able to travel. the egg could fall out of the fimbrae
what can inhibit implantation
imbalance of progesterone and estrogen; large doses of progesterone can delay or inhibit ovulation, prevent fertilization, or render the uterus unready for implantation
