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GIGU > Fertilization and Implantation > Flashcards

Fertilization and Implantation Flashcards

1
Q

What day c/t the menstrual cycle does fertilization occur?

A

Day 15-16

*allows for recombination of genetic material

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2
Q

Where does fertilization occur?

A

ampulla of oviduct

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3
Q

What leads to follicular rupture so oocyte can be swept into the oviduct by fimbriae for fertilization?

A

LH surge

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4
Q

How does an oocyte get into the oviduct from the ovary during ovulation for potential fertilization?

A

ovum and corona radiata released into peritoneum via LH surge, picked up by fimbriae and swept into oviduct

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5
Q

What million sperm/ejaculate is considered infertile?

A

less than 20

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6
Q

Out of the 300 million sperm that enter the vagina and uterus, how many reach the ampulla of the oviduct?

A

200

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7
Q

What helps sperm reach the ampulla in terms of contractions?

A

Myometrium contract from cervix to fundus to help sperm move up to oviduct

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8
Q

What hormone causes myometrial contractions that help sperm reach oviduct?

A

increased ESTROGEN near ovulation period

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9
Q

Generally describe sperm capacitation

A

Sperm are coated with surface molecules in epididymis, more seminal proteins added via semen, all removed in uterus to expose binding molecules for zona pellucida

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10
Q

Why do incapacitated sperm bind to the epithelial cells in the isthmus of the ovidcut?

A
  • It slows capacitation process
  • –>release when capacitated
  • extends sperm lifespan by several days
  • increases probability they will be in the oviduct when the egg is ovulated/released into oviduct
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11
Q

What occurs with hyperactivation of sperm during capacitation?

A

changes in flagella motion d/t chemical signals from oocyte

  • ->wave like to whip like
  • ->NECESSARY for sperm to detach from isthmus epithelium
  • ->increases mobility
  • ->helps propel sperm through outer layers of egg to the plasma membrane
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12
Q

What barriers must be breached on the egg for fertilization to occur?

A
  • corona radiata/cumulus
  • zona pellucida
  • plasma membrane of oocyte
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13
Q

What is the corona radiata matrix primarily made of?

A

hyaluronic acid

–>digested by sperm hyaluronidase

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14
Q

What glycoproteins compose the zona pellucida?

A

ZP1
ZP2
ZP3
ZP4

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15
Q

What zona pellucida receptors are on sperm after capacitation?

A

ZP3

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16
Q

What triggers the acrosome reaction?

A

binding of ZP3 receptor on sperm to ZP3 on egg

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17
Q

What is the acrosome reaction?

A

-inner sperm PM fuses with outer acrosomal membrane to release contents of sperm

—>digest zona pellucida so sperm can enter

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18
Q

What is the next barrier for sperm to get through after zona pellucida/acrosome reaction?

A

plama membrane of oocyte

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19
Q

How does sperm enter the egg during fusion of PM?

A

sperm has protein called IZUMO that binds recepter on oocyte

–>sperm enters, DNA decondenses and pronucleus forms around it

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20
Q

What is the cortical reaction?

A

fusion of sperm and egg releases Ca++
–> alters ZP proteins to block additional sperm
–> hyaluronic acid and other proteoglycans released
–> ZP forms physical
barrier

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21
Q

What is the purpose of the cortical reaction?

A

prevent polyspermy

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22
Q

What triggers the cortical reaction?

A

fusion of sperm and egg

23
Q

What stimulates completion of meiosis II after cortical reaction?

A

Ca++

–>breakdown of MAPK proteins

–>2nd polar body released

24
Q

Describe egg activation

A

+ as sperm DNA condenses

  • ->pronucleus forms around female chromosomes after finished meiosis II
  • ->M and F DNA replicate as the pronuclei move together
  • ->Fusion of pronuclei + first embryonic cleavage
25
Q

What is considered the beginning of embryonic development?

A

fusion of M and F pronuclei

26
Q

What day does the embryo reach morula (16 cell)?

A

3

27
Q

What day does the embryo reach early blastocyst?

A

4

28
Q

What day does the blastocyst implant?

A

6-8

29
Q

What cells are considered totipotent?

A

blasomeres

—>individual cells in morula

30
Q

What do outer cells of morula become?

A

increase cell-cell adhesion via desmosomes and tight jxns
–>form Trophoectoderm

*increase sodium transport and osmosis to form the blastocele

31
Q

What do the inner cells of the morula become?

A

inner cell mass

–>forms embryo

32
Q

What cell is pluripotent?

A

inner cell mass of morula

33
Q

What happens to the zona pellucida prior to implantation?

A

hatches from embryo via:

–>trophoblasts secrete proteases to digest ZP

34
Q

What can inability of zona pellucida to hatch cause?

A

infertility

35
Q

What can premature hatching of zona pellucida cause?

A

abnormal implantation

36
Q

What is the fxn of blastocyst in terms of maintenance of pregnancy?

A

synthesizes and secretes molecules to:

  • promote maintenance of pregnancy
  • promote implantation and placental development

–>also secretes immunosuppressive factors

37
Q

What secretes hCG?

A

trophoblasts

syncytiotrophoblasts

38
Q

When is hCG measurable in blood after ovulation?

A

8 days post ovulation

39
Q

What structure is hCG related to?

A

LH

40
Q

What is the fxn of hCG?

A

prevents involution of corpus luteum

  • –>prevents menstruation
  • –>leads to increased secretion of progesterone and estrogen
  • autocrine fxns
  • ->stimulates trophoblast growth and development
  • –>stimulates placental growth
41
Q

What are the autocrine fxns of hCG?

A
  • stimulates trophoblast growth and development

- stimulates placental growth

42
Q

What hormones does hCG stimulation affect?

A

increased progesterone and estrogen

43
Q

What are the stages of implantation?

A

1: apposition
2: attachment
3: invasion

44
Q

Describe apposition phase of implantation

A

Contact between crypt in endometrium and trophoblasts

–>inner cell mass rotates to face endometrial epithelium

45
Q

Describe attachment phase of implantation

A

Trophoblasts adhere to lumibal endometrial epithelium
–>interact with surface proteins

+ decidualization

  • ->increased vascular permeability
  • ->intracellular matrix composition
  • ->stromal cell morphology
46
Q

Describe invasion phase of implantation

A

Degradation of endometrial epithelial cells

Trophoblast fusion and formation of syncytiotrophoblasts
–>protrude through basement membrane to reach endometrial stroma

47
Q

What are the three main fxns of syncytiotrophoblasts?

A

Adhesive
–>express cadherins and integrins to bind uterine ECM

Invasive
–> breakdown extracellular matrix

Endocrine
–>hCG

48
Q

What do syncytiotrophoblasts secrete?

A

hCG

–>maintains corpus luteum= progesterone secretion

49
Q

When do syncytiotrophoblasts become highly steroidogenic?

A

10 weeks

–>produce progesterone for maintenance so no longer need corpus luteum

50
Q

What are other fxns of syncytiotrophoblasts that occur during implantation and placentation?

A
  • phagocytosis

- bidirectional placental transfer of gases, nutrients and wastes

51
Q

What is decidualizaiton?

A

response of maternal stromal cells to invasion and progesterone

52
Q

Describe decidualization

A

endometrial stroma transformed into enlarged and glycogen-filled decidual cells

  • -> prepare for implantation
  • -> has adhesive jxns that limit migration of embryo
  • -> secretes signals to prevent embryo from invading myometrium
53
Q

Is there decidualization in ectopic pregnancies?

A

NO

GIGU (37 decks)

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