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HBSF Block 1 > Embryology Lecture 2 Ovulation to Implantation: Week 1 > Flashcards

Embryology Lecture 2 Ovulation to Implantation: Week 1 Flashcards

1
Q

Fertilization is a process of several events and typically takes place in the ______ of the uterine tube

A

ampulla

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2
Q

True or False: Fertilization occurs within 48 hours of ovulation.

A

False, 24

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3
Q

What are the 3 main phases of fertilization?

A

3 Phases:

  • Penetration of corona radiata
  • Binding and penetration of zona pellucida
  • Fusion of membranes of secondary oocyte and spermatozoa
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4
Q

What happens during penetration of corona radiata?

8.5.6

A

¨The sperm uses both chemical and physical means

The action of membrane-bound enzyme hyaluronidase on its coat

Swimming motion of its flagellum

8.5.6

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5
Q

What happens during the binding and penetration of zona pelluicida? (3 steps)

A

Sperm binds with ZP3 receptor present on zona pellucida

This triggers acrosome reaction resulting in the release of acrosomal enzymes:

ACROSIN (acrosin digests zona pellucida at the site of discharge, enabling the sperm to reach the cell membrane)

Sperm contact with the cell membrane of a secondary oocyte triggers CORTICAL REACTION:

Causes release of cortical granules (lysosome) from oocyte cytoplasm:

  • both zona pellucida and oocyte membrane become impermeable to other sperms (prevents polyspermy)
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6
Q

What happens during the fusion of membranes of secondary oocyte and spermatozoon?

A

Entire sperm except the cell membrane enters into the cytoplasm of oocyte

Sperm mitochondria and tail degenerate

All mitochondria in the embryo (and all mitochondrial DNA) come from the mother

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7
Q

As soon as the sperm enters the oocyte…..

A

¨Second meiotic division completes resulting in the formation of:

Definitive oocyte:

Oocyte has a vesicular nucleus:

Pronucleus

Oocyte is metabolically activated

Oocyte pronucleus fuses with sperm pronucleus

8.5.6

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8
Q

Summary of Fertilization Phases

8.5.6

A

8.5.6

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9
Q

Summary of Fertilization Phases Flow Chart

A
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10
Q

A new fertilized human oocyte

A
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11
Q

What are the 3 results of fertilization?

A
  • Diploid chromosome number is restored
  • Sex of the fetus is determined (XX-female, XY- male)
  • Cleavage begins (a series of mitotic cell divisions within the zygote)
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12
Q

What happens during the two-cell stage of cleavage?

A

¨Individual cells:

blastomeres

Mitotic divisions maintain diploid(2n) chromosome configuration

Cells become smaller

Blastomeres are totipotent (can become any type of cell)

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13
Q

What happens in the 4 cell stage of cleavage?

A

Second cleavage results in 4 equivalent blastomeres

Still in zona pellucida

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14
Q

What happens in the 8 cell stage of cleavage?

A

Third cleavage results in 8 blastomeres

The blastomeres are still equivalent

Zona pellucida present

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15
Q

What happens after 8 cell stage?

A

Compaction is caused by:

Increased cell-cell adhesion

Outer layer of cells with tight junctions

Inner layer communicate by gap junctions

Cells that are forced to the outside are destined to become trophoblast cells that will form the placenta

The i_nner cells_ will form the embryo and are called the inner cell mass

BLASTOMERES ARE TOTIPOTENT CELLS

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16
Q

16 cell stage embryo looks like a mulberry and is called ______. Explain its characteristics

A

Still surrounded by zona pellucida

Consists of:

Inner cell mass or embryoblast:

Gives rise to embryo proper

Outer cell mass or trophoblast:

Forms the placenta and provides nutrition to the embryo

Forms 3-4 days after fertilization

17
Q

Explain what forms after the morula?

A

Cavitation

A fluid-filled cavity forms inside the morula

This cavity is known as the blastocyst cavity or blastocele, and the morula is now called a blastula or blastocyst

The inner cell mass is now known as the embryoblast and the outer cell mass becomes the trophoblast

Note that the embryo is still contained in the zona pellucida

18
Q

What happens during late blastocyst?

A

At day 5 the blastocyst shows polarity:

Embryonic or animal pole

Side of blastocyst to which inner cell mass is attached

Abembryonic pole

Opposite side

19
Q

A mature blastocyst consists of what 3 structures?

A

A mature blastocyst consists of:

Inner cell mass ( embryoblast), trophoblast (outer cell mass) and blastocele

20
Q

Human embryo development in culture

A

8.5.6

21
Q

How does twinning work?

A

A: Cleavage of an early embryo with each half developing as a completely separate embryo.

B: Splitting of the inner cell mass of a blastocyst and the formation of two embryos enclosed in a common trophoblast. This is the most common mode of twinning.

C: The inner cell mass does not completely separate, or if portions of the inner cell mass secondarily rejoin, conjoined twins may result.

22
Q

______ of the embryo from zona pellucida occurs just prior to implantation

Inability to _______ results in Infertility

_______ results in abnormal implantation in the uterine tube

A

Hatching

hatch

Premature hatching

23
Q

One major function of the ______ is to prevent premature implantation

8.5.6

A

zona pellucida

8.5.6

24
Q

______ is the process by which the blastocyst embeds itself into the endometrium of the uterus

A

Implantation

8.5.6

25
Q

Descrobve what normal implantation is

8.5.6

A

•Normal implantation site: Posterior superior wall of the endometrium in the

functional layer, during the secretory phase of the menstrual cycle

• Time:

7days after fertilization

• Before implantation trophoblast proliferate and start differentiating into cytotrophoblast and syncytiotrophoblast

26
Q

Describe the process of normal implantation

A

The polar trophoblasts touch the endometrium and secrete proteolytic enzymes which dissolve the endometrium

The trophoblast becomes two-layered:

Syncytiotrophoblasts

Cytotrophoblasts

Syncytiotrophoblasts invade the endometrial stroma

The embryo is partially embedded in the endometrium

27
Q

What is placental Previa? How can you diagnose it?

A

When implantation occurs in the lower parts of the uterus towards the cervix

This makes it easy for the placenta to tear, and the mother can die from hemorrhage, or the placenta may grow to obstruct the cervical canal

Can be diagnosed with ultrasound, and the baby is delivered via Cesarean section

28
Q

What is the term for pregnancy outside of the uterus?

A

Ectopic pregnancy

Tubal – most common

Ovarian

Abdominal

29
Q

Ectopic Implantation Summary

A

Endometriosis: Presence of endometrium like tissue in abnormal locations. Endometriosis most commonly involves ovaries, fallopian tubes and the tissue lining the pelvis.

8.5.6

30
Q

Week 1 General Summary

8.5.6

A

8.5.6

31
Q

Summary of 1st Week of Development (Day 1- 7)

A
32
Q
A

HBSF Block 1 (14 decks)

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