SFP: embryology week one

Question 1

what are corona radiata cells?

Answer 1

cells packed around the exterior of the egg

Question 2

what is the zona pellucida?

Answer 2

the region directly deep to the corona radiata in an egg

Question 3

name the three major steps required in fertilization

Answer 3

capacitation, acrosome reaction, zona reaction

Question 4

describe capacitation

Answer 4

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

Question 5

describe the acrosome reaction

Answer 5

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

Question 6

describe the zona reaction

Answer 6

prevents polyspermia; the properties of the zona pellucida change to make it impermeable to other sperm

Question 7

what sperm receptor is used to connect to the egg?

Answer 7

ZP3

Question 8

acrosome reaction is a ___ dependent event

Answer 8

calcium

Question 9

what is an important enzyme released prior to the acrosome reaction? what important enzyme is released during the acrosome reaction?

Answer 9

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

Question 10

describe the zona reaction

Answer 10

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.

Question 11

describe the developing features of the zygote during week one

Answer 11

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

Question 12

when is the zygote ready for implantation?

Answer 12

at the end of week one when the zona pellucida degenerates

Question 13

describe dizygotic twins

Answer 13

two egg, two sperm. they can develop completely separately or can have a fused placenta.

Question 14

describe monozygotic twins

Answer 14

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

Question 15

does a fused placenta cause issues?

Answer 15

typically no

Question 16

if the ___ doesn’t split far enough apart, it can cause conjoined twins

Answer 16

inner cell mass

Question 17

name the different types of development in relation to placenta and amniotic cavity with monozygotic twins

Answer 17

dichorionic: two placentas
monochorionic: one placenta

diamniotic: two different amnions
monoamnionic: one amnion

Question 18

describe the forms of trophoblasts

Answer 18

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

Question 19

in week two, the inner mass cells form….? describe their positions.

Answer 19

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.

Question 20

which trophoblast type eventually becomes part of the placenta?

Answer 20

cytotrophoblasts

Question 21

what are primary chorionic villi

Answer 21

peaks in the cytotrophoblasts that will eventually form the placenta

Question 22

what are secondary villi

Answer 22

a mesenchyme core that forms directly deep to the primary villi

Question 23

what causes ectopic pregnancy?

Answer 23

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

Question 24

what can inhibit implantation

Answer 24

imbalance of progesterone and estrogen; large doses of progesterone can delay or inhibit ovulation, prevent fertilization, or render the uterus unready for implantation