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GI/GU Exam > Fertilization and Implantation > Flashcards

Fertilization and Implantation Flashcards

1
Q

What happens during capacitation? Why is it important?

A
  • The sperm becomes hyper-activated; the motion of the flagella changes from wave-like to whip-like
  • Important to help propel sperm though outer layer of egg to reach its membrane
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2
Q

What days do fertilization typically occur?

A

days 15-16 of menstrual cycle

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3
Q

Where do incapacitated sperm bind? Why is the binding important?

A
  • to the epithelial cells of oviductal isthmus
  • binding slows capacitation process and extends sperm lifespan, increasing probability that sperm will be in oviduct when egg is ovulated
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4
Q

What barriers must be breached for fertilization to occur? (3)

A
  • corona radiata
  • zona pellucida
  • plasma membrane of oocyte
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5
Q

How does the sperm breach the corona radiata?

A

It has hyaluronidase that digests the hyaluronic acid that makes up this membrane

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6
Q

How does the sperm breach the zona pellucida?

A

Sperm contains a receptor for one of the glycoproteins (ZP3), binds to it causing the acrosome reaction so enzymes can digest the zona pellucida

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7
Q

What is the acrosome reaction?

A

When the inner sperm plasma membrane fuses with the outer acrosomal membrane to release contents of the acrosomal vesicle (enzymes that make holes in ZP)

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8
Q

How does the sperm breach the egg plasma membrane?

A

Has a protein called Izumo, and binds to Izumo receptor on oocyte, fusing with it

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9
Q

What does the fusion of the sperm and the egg trigger?

A

the cortical reaction

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10
Q

What happens during the cortical reaction? Why is it important?

A
  • Calcium is released
  • ZP proteins altered
  • ZP solidifies, forming a physical barrier

THIS PREVENTS POLYSPERMY

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11
Q

What does calcium release from cortical reaction stimulate?

A

the egg to complete meiosis II

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12
Q

What happens during the first week of embryonic development? (2)

A
  • embryo reaches morula stage (day 3) then early blastocyst stage (day 4)
  • implantation occurs (days 6-8)
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13
Q

What is the potency of the blastomeres?

A

they are totipotent

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14
Q

What is the potency of the inner cell mass?

A

it is pluripotent

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15
Q

What must happen before the embryo can implant?

A

It must hatch from the zona pellucida

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16
Q

How does hatching occur?

A

trophoblasts secrete proteases that digest the ZP

17
Q

What can happen if the egg hatches prematurely?

A

abnormal implantation

18
Q

What does the blastocyst secrete/synthesize in preparation of maintenance of pregnancy?

A
  • secretes immunosuppressive and immunoregulatory factors
19
Q

What is hCG secreted by? (2)

A
  • trophoblasts

- syncytiotrophoblasts

20
Q

What is the function of hCG?

A
  • prevents involution of corpus luteum, preventing menstruation and increasing secretion of progesterone and estrogen
  • is an autocrine growth factor, stimulating trophoblast and placental growth
21
Q

What are the stages of implantation? (3)

A
  • apposition
  • attachment
  • invasion
22
Q

What happens during the attachment stage?

A

Trophoblast cells adhere to endometrial epithelium, initiate decidualization

23
Q

What changes happen during decidualization? (3)

A
  • increased vascular permeability
  • intracellular matrix composition changes
  • stromal cell morphology
24
Q

What happens during the invasion stage? (3)

A
  • the endometrial epithelial cells degrade
  • trophoblast fuses and syncytiotrophoblast is formed
  • syncytiotrophoblast protrudes through the basement membrane and reaches endometrial stroma
25
Q

What do the syncytiotrophoblasts do? (4)

A
  • express adhesive surface proteins
  • breaks down extracellular matrix
  • secretes hCG
  • makes steroids at 10 weeks
26
Q

What is one thing that can happen if decidualization goes wrong? Why does it happen?

A
  • postpartum hemorrhage

- this can happen if the signals that normally prevent the embryo from invading the myometrium fail

27
Q

Where is the most common site of ectopic implantation?

A

Oviduct

28
Q

What DOES NOT happen during ectopic implantation? What are the consequences?

A
  • Decidualization doesn’t happen

- invasion isn’t controlled, ruptures tissues and causes hemorrhage

29
Q

What happens during placentation? (3)

A
  • lacunae form w/in syncytiotrophoblasts
  • maternal capillaries broken
  • lacunae fill with endometrial secretions, maternal blood, digested matrix for nutrient transfer
30
Q

What day approximately does placentation occur?

A

Day 9

31
Q

What happens in the primary villi?

A

syncytiotrophoblasts and cytotrophoblasts go to lacunae

32
Q

What happens in the secondary villi?

A

mesenchymal cells from extraembryonic mesoderm invade villi

33
Q

What happens in the tertiary villi?

A

mesenchymal cells form blood vessels

GI/GU Exam (21 decks)

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