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GIGU Final > Fertilization and Implantation > Flashcards

Fertilization and Implantation Flashcards

1
Q

When does fertilization occur?

A

~day 15-16 of the menstrual cycle

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2
Q

where does the sperm bind on the oocyte?

A

zona pellucida

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3
Q

what triggers the exocytosis of the acrosome (acrosomal reaction)?

A

a rise in Ca2+ inside the sperm

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4
Q

what is the purpose of the hydrolytic enzymes that are housed within the acrosomal cap?

A

they locally dissolve the zona pellucida

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5
Q

what is the cortical reaction?

A

there is exocytosis of granules that lead to changes in the zona pellucida proteins causing the zona pellucida to harden and prevent the entry of other sperm

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6
Q

what causes the cortical reaction?

A

a rise in Ca2+ concentration inside the oocyte

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7
Q

what specifically induces the completion of the oocyte’s second meiotic division and the formation of the second polar body?

A

the rise in Ca2+ levels inside the oocyte (with fertilization)

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8
Q

where must both the sperm and the oocyte travel to for fertilization to occur?

A

to the ampulla of the oviduct

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9
Q

about how many sperm actually reach the ampulla of the oviduct?

A

~200

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10
Q

what helps to move the sperm through the cervix/uterus?

A

myometrium contractions that are a result of increased estrogen near the ovulation period

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11
Q

what hormone actually causes down regulation to prevent immune cells from attacking the egg or the sperm?

A

progesterone

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12
Q

What is sperm capacitation?

A

when sperm are exposed to the female tract environment, the seminal plasma coatings along with some of the surface molecules are removed- thus exposing portions of the molecules that can bind to the zona pellucida of the oocyte

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13
Q

where do incapacitated sperm bind?

A

to the epithelial cells of the oviductal isthmus

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14
Q

why do sperm bind to the epithelial cells of the oviductal isthmus?

A

it slows the capacitation process and extends sperm lifespan, which increases the probability of the sperm being in the oviduct when the egg is ovulated

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15
Q

what is associated with sperm capacitation and chemical signals from the oocyte?

A

hyperactivation of sperm

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16
Q

what does hyperactivation of sperm involve and why is it important?

A

it involves a change in flagella motion from wave-like to whip like; it is necessary for sperm to detach from the epithelium of the oviduct and it increases mobility; helps propel sperm through the outer layers of the oocyte

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17
Q

for fertilization, 3 barriers must be breached. What are these barriers?

A

the expanded cumulus (corona radiata), the zona pellucida, and the plasma membrane of the oocyte

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18
Q

what is the predominant composition of the cumulus cell matrix?

A

hyaluronic acid

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19
Q

how do sperm digest the cumulus cell matrix (aka the hyaluronic acid)?

A

via membrane bound hyaluronidase

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20
Q

what zone pellucida receptor do sperm contain?

A

ZP3 receptors, which are available after capacitation

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21
Q

what does binding of the ZP3 receptor on sperm to the ZP3 glycoprotein trigger?

A

the acrosome reaction

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22
Q

what happens during the acrosome reaction?

A

the inner sperm plasma membrane fuses with outer acrosomal membrane to release contents of the acrosomal vesicle

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23
Q

what do the enzyme in the acrosomal vesicle do?

A

digest the zona pellucida

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24
Q

how does the sperm bind to the oocyte’s plasma membrane?

A

sperm possess a protein called Izumo, which binds to the Izumo receptor on the oocyte

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25
Q

what happens once the sperm binds to the izumo receptor on the oocyte’s plasma membrane?

A

the entire sperm enters the egg during fusion, and the sperm DNA instantly de-condenses

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26
Q

what forms around the sperm’s DNA once inside the oocyte’s plasma membrane?

A

a pronucleus

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27
Q

what does the cortical reaction prevent?

A

polyspermy

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28
Q

how does the completion of meiosis II begin?

A

by the breakdown of MAPK proteins

29
Q

when does egg activation occur?

A

as the sperm DNA condenses

30
Q

what initiates the first embryonic cleavage?

A

the fusion of the pronuclei (signifies the beginning of embryonic development)

31
Q

what is cleavage?

A

cell division without growth

32
Q

when does the embryo reach ~ the 16 cell stage morula?

A

day 3

33
Q

when is the embryo considered an early blastocyst?

A

~day 4

34
Q

when does implantation occur?

A

around day 6-8

35
Q

what are the individual cells called in a blastocyst?

A

blastomere

36
Q

what do the mitotic divisions maintain in the embryonic cleavage?

A

2N (diploid) complement

37
Q

what are blastomeres known to be?

A

totipotent

38
Q

what is blastocele development?

A

the outer cells of the morula increase their cell adhesion molecules (desmosomes and tight junctions)- this forms a trophoectoderm, which allows for an increase in Na+ transport and osmosis to form a blastocele

39
Q

what do the cells from the inner morula eventually form?

A

the embryo proper

40
Q

what are the cells from the inner morula known to be?

A

pluripotent (if you split in half, we could have identical twins)

41
Q

as the embryo continues to grow and prior to the implantation of the embryo, what needs to happen?

A

the blastocyst needs to hatch- the embryo needs to hatch from the zona pellucida

42
Q

how does blastocyst hatching occur?

A

the trophoblasts secrete proteases that digest the zona pellucida

43
Q

what does an inability to hatch from the zona pellucida result in?

A

infertility

44
Q

what does premature hatching from the zona pellucida result in?

A

abnormal implantation

45
Q

following the hatching from the zona pellucida, what does the blastocyst begin synthesizing and secreting?

A

molecules that promote the maintenance of pregnancy, promote implantation and placental development

46
Q

what is hCG secreted by?

A

trophoblasts and syncytiotrophoblasts following implantation

47
Q

when is hCG measurable in blood?

A

~8 days post ovulation

48
Q

what is the hCG structure closely related to?

A

LH

49
Q

what does hCG prevent?

A

the involution of the corpus luteum (prevents menstruation and leads to increased secretion of progesterone and estrogen which will aid in early maintenance of the pregnancy)

50
Q

what does it mean when it is said that hCG is an autocrine growth factor?

A

it stimulates trophoblast growth and development and it stimulates placental growth

51
Q

what is considered the first “stage” of implantation?

A

apposition- contact between the endometrium and the trophoblasts (typically occurs in a crypt of the endometrium)

52
Q

once apposition occurs, where does the inner cell mass of the blastocyst rotate?

A

near the endometrial epithelium

53
Q

what is the second stage of implantation, following the apposition?

A

attachment-the trophoblast cells adhere to the endometrial epithelium

54
Q

what does the stage of attachment initiate?

A

changes in the endometrial stroma (decidualization)

55
Q

what is the result of decidualization?

A

increased vascular permeability, changes in the intracellular matrix, and the cells take on a more stromal cell morphology

56
Q

what happens after decidualization/ attachment?

A

invasion-degradation of the endometrial epithelial cells

57
Q

what happens during invasion?

A

trophoblast fusion and formation of syncytiotrophoblasts

58
Q

what do syncytiotrophoblasts express?

A

adhesive surface proteins (cadherins and integrins)

59
Q

how do the syncytiotrophoblast break down the extracellular matrix during invasion?

A

they secrete matrix metalloproteases and other hydrolytic enzymes

60
Q

what is the source of secretion of hCG?

A

syncytiotrophoblasts

61
Q

what is decidualization a response to?

A

maternal stromal cells responding to invasion and progesterone

62
Q

what happens to the endometrial stroma during decidualization?

A

it is transformed into enlarged and glycogen-filled decidual cells

63
Q

what does the decidua form and what is its purpose?

A

an epithelia-like sheet with adhesive junctions that inhibit migration of the implanting embryo and a production of signals that prevent the embryo from invading the myometrium

64
Q

where is the most common site for ectopic implantation?

A

oviduct

65
Q

What does not occur during an ectopic pregnancy?

A

no decidualization- so invasion is not controlled and can rupture the tissues and cause hemorrhage

66
Q

when does placentation typically occur?

A

~ day 9

67
Q

what forms the primary villi?

A

proliferation of the syncytiotrophoblasts and cytotrophoblasts to lacunae

68
Q

what forms the secondary villi?

A

mesenchyme cells from the extraembryonic mesoderm invade the villi

69
Q

what forms the tertiary villi?

A

eventually the mesenchymal cells form fetal blood vessels de novo

GIGU Final (15 decks)

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