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BMS2.22 Human Embryogenesis (MOORMAN) > Embryogenesis > Flashcards

Embryogenesis Flashcards

1
Q

Embryology begins at:

A

fertilization

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2
Q

Before fertilization, the oocyte is stalled where?

A
  • the beginning of the second meiotic division.
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3
Q

Sperm capacitation:

A
  • biochemical changes that occur to the head of the sperm that renders it able to fertilize the oocyte.
  • occurs in the female uterus and uterine tube.
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4
Q

What reaction allows sperm to penetrate corona radiata and zona pellucida?

A
  • acrosomal reaction
    • in vitro it takes about 20 sperms acrosomal reaction to penetrate the zona pellucida and allow one sperm to fertilize.
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5
Q

Once a sperm reaches the zona pellucida, what occurs?

A
  • The sperm then releases its acrosomal enzymes, which dissolve some of the zona to allow the sperm to reach the oocyte.
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6
Q

Sperm fusion with the oocyte plasma membrane causes:

A
  • an influx of calcium, which causes the cortical reaction.
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7
Q

What is the cortical reaction?

A
  • Enzymes from the cortical granules render the zona pellucida impermeable to other sperm, preventing polyspermia.
    • polyspermia = multiple fertilization
    • caused by the influx of calcium following sperm penetration of the oocyte plasma membrane.
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8
Q

Following the cortical reaction, what occurs?

A
  1. Sperm extrudes its contents into the oocyte.
    • ONLY nucleus, centrosome, & microtubules.
    • Sperm have no organelles, mitochondria, or RNA.
  2. Oocyte completes the 2nd meiotic division.
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9
Q

All the events taking place in the zygote for the first 2-3 weeks following fertilization are controlled by:

A
  • mRNA already in the oocyte at the time of fertilization (maternal mRNA).
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10
Q

Following the oocyte completing the 2nd meiotic division, what occurs?

A
  • sperm and oocyte nuclei fuse to form zygote
    • restoration of dipoid (2n) cell
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11
Q

What event is the beginning of embryonic development?

A
  • zygote formation when the sperm and oocyte nuclei fuse
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12
Q

What occurs immediately following zygote formation?

A
  • Sex of the embryo is determined.
  • 1st mitotic division begins.
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13
Q

Sequence of events during the cortical reaction:

A
  1. sperm fuse to oocyte plasma membrane
  2. local calcium concentration increase
  3. calcium tsunami
  4. cortical granule fusion to plasma membrane, preventing polyspermia
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14
Q

Where does fertilization normally take place?

A
  • the ampula of the uterine tube
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15
Q

What is the zone pellucida?

A
  • a glycoprotein membrane surrounding the plasma membrane of the oocyte
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16
Q

The mitotic divisions occurring the first 4 days following fertilization are:

A
  • symmetric, synchronous, and contained within the zona pellucida.
    • day 4 = morula (32 cells)
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17
Q

What occurs on post-fertilization day 5?

A
  • blastocyst forms (hollow ball)
  • blastocyst, releasing enzymes, hatches from the zona pellucida.
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18
Q

Blastocyst structure:

A
  • outer cell mass = trophoblast
  • inner cell mass = embryoblast
  • hollow cavity
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19
Q

Trophoblast:

A
  • the outer cell mass of the blastocyst that will go on to form the placenta.
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20
Q

Embryoblast:

A
  • the inner cell mass of the blastocyst that contains the “embryonic stem cells” that will go on to form the embryo.
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21
Q

On post-fertilization day 6, what occurs?

A
  • implantation of the blastocyst on the body of the uterine wall
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22
Q

How does implantation occur?

A
  • the cells of the trophoblast invade the lining of the body of the uterine wall
23
Q

While invading the lining of the uterine wall during implantation, what else are the trophoblast cells doing?

A
  1. fuse together and differentiate into a cytotrophoblast and a syncytiotrophoblast.
    • allows for regional specialization of protein production.
  2. syncytiotrophoblast begins producing human chorionic gonadotropin (hCG).
24
Q

Implantation any place other than the body of the uterus is an:

A
  • ectopic pregnancy
25
Q

What is the most common site of ectopic pregnancy?

A
  • ampulla of the uterine tube
26
Q

What is the most common site of ectopic pregnancy in the peritoneal cavity?

A
  • the rectouterine pouch
27
Q

When is human chorionic gonadotropin (hCG) detectable in the blood following pregnancy?

A
  • implantation
    • when the trophoblast implants into the body of the uterine wall, differentiates into a syncytiotrophoblast, and begins producing hCG.
28
Q

What are the two roles of the syncytiotrophoblast?

A
  • produces hCG at the time of implantation.
  • invades the uterine lining and induces vascular changes.
29
Q

Follwing implantation, the embryoblast differentiates into:

A
  • epiblast and hypoblast.
30
Q

The hypoblast of the embryoblast sits on top of:

A
  • the blastocyst cavity, which becomes the yolk sac
31
Q

The epiblast of the embryoblast sits below:

A
  • the aminotic cavity
32
Q

When is dorsal and ventral first defined in the embryogensis?

A
  • at the time of epiblast and hypoblast development during the second week.
33
Q

During what week doe the syncytiotrophoblast begin to form lacunae (hollow spaces)?

A
  • second week
  • lacunae fill with maternal blood establishing a primitive utero-placental circulation in week 3.
34
Q

When is the utero-placental circulation first noticeable?

A
  • the third week
35
Q

Connecting stalk:

A
  • suspends the embryo, with its amnion and yolk sac, in the chorionic cavity
  • stalk formed by extraembryonic mesoderm
  • formed by the end of the third week
36
Q

At the end of the third week, the hypoblast and epiblast cells adhere to each other in only 2 locations.

Which two?

A

buccopharyngeal membrane and cloacal membrane

37
Q

When does zygotic mRNA transcription begin?

A
  • the beginning of the fourth week
38
Q

What is the first indication in the fourth week that zygotic transcription has begun?

A
  • The primitive streak (groove) appears at the caudal end of the dorsal surface of the epiblast.
39
Q

The primitive streak (groove) initiates:

A

gastrulation

40
Q

Gastrulation:

A
  • turns a bilaminar embryo into a trilaminar embryo
41
Q

Morphologic assymmetry begins at the primitive groove, and is due to what protein?

A

sonic hedgehog (ssh)

42
Q

Cells in the pimitive node/pit:

A
  • all have a single cilia.
    • cilia sweeps fluid from the right hand side of the embryo to the left hand side.
    • fluid contains vesicles containing sonic hedgehog (ssh).
43
Q

The cilia of the cells of the primitive pit cause sonic hedgehog (ssh) to:

A
  • migrate from the right to the left side of the embryo.
  • ssh stimulates gene expression on the left hand side of the embryo BEFORE the right hand side.
44
Q

ssh stimulates gene expression on what side of the embryo first?

A
  • left-hand side.
  • due to primitive pit cells’ cilia.
  • sets up the morphological asymmetry of the body.
45
Q

“sidedness” of the embryo is determined at what point in embryogenesis?

A
  • gastrulation
    • when the primitive pit’s cells’ cilia stimulates movement of ssh-containing vesicles to the left side of the embryo.
46
Q

Ciliopathy:

A
  • can cause errors in the distribution of ssh during gastrulation
    • gene expression is in altered locations, morphological changes occur.

SITUS INVERSUS

47
Q

Delamination of the primitive groove gives rise to:

(epithelial to mesenchymal)

A
  • a three layer embryo:
    • ectoderm = outer region
    • mesoderm = middle region
    • endoderm = inner region
  • the cells of the primitive groove migrate in between the epiblast and the hypoblast. They completely replace the hypoblast.
48
Q

The ectoderm, mesoderm, and endoderm all arise from:

A
  • the epiblast
  • the hypoblast is completely replaced by primitive groove cells
49
Q

The epiblast cells do not invade:

A
  • the buccopharyngeal or cloacal membranes
    • because this is the only place where epiblast and hypoblast cells tightly adhere to one another.
50
Q

How is the notochord established?

A
  • epiblast cells of the primitive node migrate to the buccopharyngeal membrane on the midline
51
Q

The notochord induces development of:

A
  • the nervous system
    • after gastrulation
52
Q

What is the only remnant of the notochord in adults?

A

nucleus pulposus

53
Q

What results from the union between the sperm and the oocyte?

A
  • diploid (2n) complement of chromosomes
  • cortical reaction
  • formation of second polar body
  • completion of the oocyte’s 2nd meiotic division
54
Q

Similarities between the buccopharyngeal membrane and the cloacal membrane:

A
  • both have no mesodermal layer
  • both predict site of the future opening of gut tube
  • both visible as a shallow depression in the ectoderm
  • both will rupture

BMS2.22 Human Embryogenesis (MOORMAN) (1 decks)

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