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Embryology > Pre-embryonic period and Fetal membranes > Flashcards

Pre-embryonic period and Fetal membranes Flashcards

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1
Q

List five events of the 2-week pre-embryonic period

A

Fertilization, Transportation of the zygote through the uterine tube, Mitotic divisions, Implantation, Formation of primordial embryonic tissue

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2
Q

Cleavage begins approximately __ hours after fertilization.

A

30

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3
Q

What are the cells formed from cleavage of the zygote?

A

Blastomeres

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4
Q

Cleavage consists of ____ of the zygote resulting in increasing ____ which become _____ with each cleavage division

A

repeated mitotic division; number of cells; smaller

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5
Q

Embryonic cells (blastomeres) cleave normally as the zygote passes along the ____.

A

Uterine tube toward the uterus

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6
Q

After the third cleavage, blastomeres form a compact ball of cells held together by __ in a process called __.

A

Tight junctions; Compaction

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7
Q

Compaction permits ___ and is a prerequisite for ____.

A

Greater cell-to-cell interaction; Segregation

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8
Q

Compaction segregates ____ from ____

A

Inner cells from outer cells

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9
Q

Compaction is probably mediated by _____

A

Cell surface adhesion glycoproteins

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10
Q

What is the 16-cell stage called, and when does it appear?

A

Morula; approximately 3 days after fertilization

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11
Q

Morula is derived from?

A

Latin: Morus meaning mulberry

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12
Q

The morula is composed of what two masses?

A

Inner cell mass and outer cell mass

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13
Q

The inner cell mass gives rise to __.

A

Tissues of the embryo proper

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14
Q

The outer cell mass forms the __, which later contributes to the __.

A

Trophoblast; placenta

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15
Q

When does zona pellucida disappear?

A

By the end of the 4th day

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16
Q

When does the blastocystic cavity appear inside the morula, and how?

A

Just after morula enters uterus (~4 days post-fertilization); fluid from uterine cavity passes through zona pellucida to form the space called blastocystic cavity

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17
Q

The appearance of the __ inside the morula marks the formation of the blastocyst.

A

Blastocystic cavity

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18
Q

Fluid accumulation in the blastocystic cavity separate the blastomeres into?

A

Trophoblast (outer layer) and Embryoblast (inner cell mass)

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19
Q

Trophoblast etymology

A

Greek Trophe: nutrition

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20
Q

What is the primordium of the embryo called?

A

Embryoblast

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21
Q

What gives rise to the embryonic part of the placenta?

A

Trophoblast

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22
Q

During blastogenesis, the conceptus is called a __.

A

Blastocyst

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23
Q

During blastogenesis, the __ forms the wall of the blastocyst.

A

Trophoblast

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24
Q

The shedding and hatching of the zona pellucida permits what?

A

Rapid increase in size of the hatched blastocyst

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25
Before implantation and while floating in the uterus, how does the early embryo derive nourishment?
From secretions of the uterine glands
26
Approximately __ days after fertilization, the blastocyst attaches to the __.
6; Endometrial epithelium
27
The blastocyst attaches to the ___, usually adjacent to the __.
Endometrial epithelium; Embryonic pole
28
Once attached to the endometrial epithelium, what does the trophoblast do?
Proliferates rapidly and differentiates into two layers
29
What are the two layers formed by the differentiating trophoblast?
Cytotrophoblast (inner) and syncytiotrophoblast (outer)
30
The syncytiotrophoblast consists of a ______ protoplasmic mass in which __ can be observed.
Multinucleated; No cell boundaries can be observed
31
__ and __ modulate the differentiation of the trophoblast in carefully timed sequences.
Intrinsic factors and extracellular matrix factors
32
What separates the blastomeres into trophoblast and embryoblast?
Fluid accumulation in the blastocystic cavity
33
Endometrial epithelium is ___ to embryonic pole which is ____ to the embryoblast.
Adjacent, quickly adjacent
34
At approximately how many days post fertilisation do the fingerlike processes of syncytiotrophoblast begin to invade the connective tissue?
6 days
35
By the end of the first week, the blastocyst is ____ in the ____ of the endometrium and derives its nourishment from _____
Superficially implanted in the compact layer of the endometrium; Eroded maternal tissues
36
What part of the highly invasive syncytiotrophoblast expands quickly adjacent to the embryoblast?
The area known as the embryonic pole
37
What produces enzymes that erode the maternal tissues, enabling the blastocyst to burrow into the endometrium?
Syncytiotrophoblast
38
At approximately ____ days, a layer of cells called _____ appear on the embryoblast facing the blastocystic cavity
7 days; Hypoblast (primary endoderm)
39
What significant structure has disappeared by the time implantation begins and what event does the disappearance allow?
Zona pellucida; allows implantation to begin
40
About ____ day, trophoblastic cells over the ____ (which region?) begin to penetrate between the ____ of the ____
6th day; embryonic pole; epithelial cells of the uterine mucosa
41
What molecules are involved in attachment and invasion of the trophoblast and where are they from?
Integrins (expressed by the trophoblast), Laminin & fibronectin (extracellular matrix molecules)
42
Integrin receptors for which molecule promote attachment?
Laminin
43
Integrin receptors for which molecule stimulate migration?
Fibronectin
44
These molecules (integrins, laminin, fibronectin) interact along ____ pathways to regulate ____
signal transduction pathways to regulate trophoblast differentiation
45
Implantation is the result of mutual ____ and ____ action.
Trophoblastic and endometrial action
46
By the end of the first week, what stages has the human zygote passed through and what has began?
Morula and blastocyst stages; Implantation in the uterine mucosa
47
Disappearance of zona pellucida allows what to occur?
Implantation
48
What structure invades the uterine mucosa using integrin-mediated attachment and enzyme secretion?
Trophoblast
49
The four extra-embryonic membranes are the:
amnion, yolk sac, allantois, chorion
50
The extra-embryonic membranes are responsible for the ________, ________, ________, and ________ of the embryo and subsequent fetus.
protection, respiration, excretion, and nutrition
51
At parturition, the ________, ________, and ________ separate from the fetus and from the uterus as the afterbirth.
placenta, umbilical cord, extraembryonic membranes
52
Amnion is a thin membrane derived from _____ and ____ (germ layers?) and it loosely develops from the _____ forming _____ that is filled with ______
Ectoderm and mesoderm; embryo; an amniotic sac; amniotic fluid
53
In later fetal development, the amnion expands to come in contact with the ________.
chorion
54
As the amniotic sac enlarges during the late embryonic period (at about ____ weeks), the amnion gradually sheaths the developing ________ with an epithelial covering.
8 weeks; umbilical cord
55
Five functions of amnion
Ensures symmetrical structural development and growth; Cushions and protects by absorbing jolts received by mother; Maintains consistent pressure and temperature; Eliminates metabolic wastes; Permits freedom of fetal movement which is important for musculoskeletal development and blood flow
56
What is normally swallowed by the fetus and absorbed in the gastrointestinal tract?
Amniotic fluid
57
Amniotic fluid enters the _____, and the waste products it contains enter the _______ in the ________.
fetal blood; maternal blood in the placenta
58
Prior to delivery, the _______ is naturally or surgically ruptured, and the ________ is released.
amnion; amniotic fluid
59
What happens to amniotic fluid as the fetus grows?
Amount of amniotic fluid increases and it is continually absorbed and renewed
60
For the near-term baby, almost ________ liters of amniotic fluid are completely replaced each day.
8
61
Yolk sac is an extra-embryonic membrane established during the _____ week as cells from the _____ form _____
end of the second week; trophoblast; a thin exocoelomic membrane
62
The allantois forms during the ____ week as a _____ or ______ near the base of the ________.
third week; small outpouching or diverticulum; yolk sac
63
Remains small, involved in formation of blood cells... describe which extra-embryonic membrane?
Allantois
64
The extraembryonic portion of the allantois degenerates during the ________.
second month
65
The intraembryonic portion of the allantois involutes to form a _____ called the ________.
a thick urinary tube called the urachus
66
After birth, the urachus becomes a fibrous cord called the ________ that attaches to the _____.
median umbilical ligament; urinary bladder
67
The chorion contributes to the formation of the ______ as small fingerlike projections called ________ penetrate deeply into the uterine tissue.
placenta; chorionic villi
68
Initially, the entire surface of the chorion is covered with ________.
villi
69
The chorionic villi on the surface toward the _____ gradually degenerate producing a smooth, bare area known as ______
Uterine cavity; Smooth chorion (chorion leave)
70
The chorionic villi associated with the _____ rapidly increase in number and branch out to form a portion of chorion known as _____
Uterine wall; Villous chorion (chorion frondosum)
71
What is the outermost extraembryonic membrane?
Chorion
72
____ ensures symmetrical structural development and growth in the fetus.
Amnion
73
____ contributes to development of urinary bladder
Allantois
74
____ contributes to formation of the placenta
Chorion
75
____ gives rise to fetal umbilical arteries and vein
Allantois
76
Freedom of fetal movement permitted by amnion is important for ____ and ___
Musculoskeletal development and Blood flow
77
The smooth chorion (chorion laeve) is produced by degeneration of chorionic villi on the surface toward the ________.
uterine cavity
78
Which part of the chorion increases in number and branches out as implantation progresses?
villous chorion (chorion frondosum)
79
The villous chorion (chorion frondosum) is the portion of the chorion associated with the ________.
uterine wall
80
Monozygotic twins develop from ________ by splitting at various stages of development (from ____ to ____).
one zygote; from 2 cell stage to the blastocyst stage
81
The stage of splitting in monozygotic twins affects the overall structure of _____ and ____
the embryo and extraembryonic membranes
82
The _______ determines whether the twins will have seprate or shared ____ and ____
timing of embryonic splitting; placentas and amniotic sacs
83
Early splitting at the morula stage (Days 1–3) results in _____ twins.
dichorionic, diamniotic (DCDA). Each twin has its own placenta and amniotic sac
84
Splitting at the blastocyst stage (Days 4–7) results in _____ twins
monochorionic, diamniotic (MCDA); twins that share a placenta but have separate amniotic sacs; Twin-Twin Transfusion Syndrome (TTTS) is possible
85
Splitting during Days 8–12 results in what type of monozygotic twins?
monochorionic, monoamniotic (MCMA). Twins share both the placenta and the amniotic sac; Cord entanglement
86
Very late splitting (after Day 13) results in what condition?
Conjoined twins. Results from incomplete separation of the embryonic disc.
87
Conjoined twins develop from a single ________.
fertilized ovum
88
What is the female-to-male ratio in conjoined twins?
3:1
89
The occurrence of conjoined twins is 1 in ________ births.
40,000
90
The occurrence of conjoined twins is 1 in ________ live births.
200,000
91
Conjoined twins may be caused by any number of factors, being influenced by ______ and _______ conditions
Genetic and environmental conditions

Embryology (12 decks)

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