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Embryology > Germinal Period > Flashcards

Germinal Period Flashcards

1
Q

What’s the duration of the germinal period?

A

The first 3 weeks

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2
Q

What is the duration of the embryonic period?

A

The end of the 3rd week to the end of the 8th week

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3
Q

What is the duration of the fetal period?

A

The beginning of the 3rd month to the end of pregnancy

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4
Q

Where does fertilization occur?

A

In the ampullary region of the uterine tube

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5
Q

What must happen before the oocyte can be fertilized?

A

Capacitation

Acrosome reaction

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6
Q

What is capacitation?

A

Period of conditioning in the female reproductive tract that lasts approximately 7 hours

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7
Q

What is acrosome reaction and when does it happen?

A

Occurs after binding to the Zona pellucida and induced by Zona proteins

The release of enzymes needed to penetrate the zona pellucida, including acrosin and trypsin like-substances

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8
Q

what is phase 1 of fertilisation ?

A

penetration of the corona radiata

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9
Q

what is phase 2 of fertilisation ?

A

penetration of the zona pellucida

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10
Q

what is the zona ?

A

Zona is a glycoprotein shell that
facilitates & maintains sperm binding
& induces the acrosome reaction.

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11
Q

what does acrosin do ?

A

allows sperm to penetrate the zona & contacts plasma

membrane of the oocyte which result in release of lysosomal enzymes from the oocyte.

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12
Q

what is phase 3 of fertilisation?

A

fusion of the oocyte & sperm cell membranes.

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13
Q

what happens after the sperm enters the cytoplasm of the ovum ?

A

Cortical & zona reaction
Resumption of 2nd meiotic division
Male nucleus becomes swollen and come in contact with the nucleus of the definitive oocyte

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14
Q

what is the Cortical & zona reaction?

A

The oocyte release lysosomal enzymes from cortical
granules that prevent polyspermy, through:
- The oocyte membrane becomes impenetrable to other
spermatozoa.
- The zona pellucida alters its structure & composition to
prevent sperm binding & penetration.

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15
Q

what is the Resumption of 2nd meiotic division ?

A

-The secondary oocyte finishes its 2nd meiotic division immediately after entry of the spermatozoon.
-This result in formation of the definitive oocyte (22+X),
& the second polar body .

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16
Q

what is the name given to swollen nuclei?

A

pronuclei

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17
Q

what are the main results of fertilisation?

A

Formation of the zygote.
Restoration of diploid number of chromosomes
Determination of the sex of the new individual
Initiation of cleavage & migration of the zygote to the
site of implantation.

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18
Q

how many days after fertalisation does the blastocyst develop ?

A

4th day

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19
Q

what is the morula?

A

the 16 cell stage, 3 days after fertilisation

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20
Q

on what day does the zona pellucida start to degenerate?

A

the 4th day

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21
Q

what happens on the 5th day after fertilisation ?

A

The blastocyst reaches the uterine
cavity and begins to penetrate between the epithelial cells of the uterine mucosa (implantation) about the 6th day of fertilisation

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22
Q

what are the cells of the outer cell mass of the blastocyst called ?

A

trophoblast

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23
Q

what are the cells of the inner cell mass of the blastocyst called ?

A

embryoblast

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24
Q

what cells will form the fetal membrane and the placenta ?

A

trophoblast

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25
Q

what is the Blastocele?

A

the cavity of the blastocyst

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26
Q

what is the Embryonic pole?

A

the side of blastocyst

that corresponds the embryoblast.

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27
Q

what is the Abembryonic pole?

A

is the opposite side of the embryonic pole of the blastocyst.

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28
Q

what is implantation and when does it occur?

A 
It is the process by which the
blastocyst becomes embedded in
the superficial compact layer of the
endometrium.
• It starts at the 6th-7th day & is
completed about the 11th- 12th day after fertilisation.
29
Q

describe what happens during the implantation stage

A 
The trophoblast begin to erode 
epithelium of endometrium
forming a penetration defect.
• The blastocyst enters the
endometrium through the defect & become
implanted into it.
• After complete embedding, penetration defect is closed by a fibrin clot
30
Q

what are examples of contraceptive methods?

A 
Barrier techniques - male and female condoms 
The contraceptive pill
Depo-Provera
A male “pill”
The intrauterine device (IUD)
Vasectomy & tubal ligation
31
Q

what happens with regards to implantation on the 8th day of development?

A

the blastocyst is partially embedded in the

endometrium.

32
Q

what happens with regards to implantation on the 9th and 10th day of development?

A

the blastocyst become larger & more deeply implanted & the penetration defect becomes closed by a fibrin clot.

33
Q

what happens with regards to implantation on the 11th and 12th day of development?

A

the blastocyst is completely embedded & the defect is covered by epithelium.

34
Q

what happens with regards to implantation on the 13th day of development?

A

is complete with closure of the penetration defect by

epithelium.

35
Q

what happens with regards to the Embryoblast on the 8th day of development?

A 
The cells become organized to
form a bilaminar germ disc
formed of 2 layers:
- Hypoblast layer: small cuboidal
cells adjacent to the blastocyst
cavity.
- Epiblast layer: high columnar cells
adjacent to the amniotic cavity.
36
Q

what happens with regards to the Embryoblast on the 9th and 10th day of development?

A

no marked changes.

37
Q

what happens with regards to the Embryoblast on the 11th and 12th day of development?

A

no marked changes.

38
Q

what happens with regards to the Embryoblast on the 13th day of development?

A

no marked changes.

39
Q

what happens with regards to the Trophoblast on the 8th day of development?

A

The part of the trophoblast lying over the embryonic pole become differentiated into 2 layers:
• Outer zone: syncytiotrophoblast.
• Inner zone: cytotrophoblast.

40
Q

what happens with regards to the Trophoblast on the 9th and 10th day of development?

A

Trophoblast: the whole cells become
differentiated into cyto. & syncytiotrophoblast.
• Small spaces called vacuoles appear in trophoblast at the embryonic pole.
• These vacuoles fuse, forming large lacunae & this phase of trophoblast development is the lacunar stage.

41
Q

what happens with regards to the Trophoblast on the 11th and 12th day of development?
(this answer is very long)

A
  • Syncytiotrophoblast:
    • The lacunar spaces form an intercommunicating network.
    • The cells penetrate deeper & erode the endothelial lining of the maternal capillaries (sinusoids).
    • The lacunae become continuous with the sinusoids & maternal blood enters the lacunar system.
  • Cytotrophoblast:
    Formation of extraembryonic mesoderm:
    • Cells of the inner surface of the cytotrophoblast forms a very loose tissue called extraembryonic mesoderm between the inner surface of the cytotrophoblast & the outer surface of the primitive yolk sac cavity.
    • The trophoblast will be called the chorion & the blastocyst is now called chorionic vesicle.
  • Formation of the extraembryonic coelom:
    • Large cavities develop in the extraembryonic mesoderm forming a new space known as the extraembryonic coelom, or chorionic cavity.
    • The chorionic cavity: divides the extraembryonic mesoderm into:
    • Extraembryonic somatopleuric mesoderm lining the cytotrophoblast & amnion.
    • Extraembryonic splanchnopleuric mesoderm covering the yolk sac.
42
Q

what happens with regards to the Trophoblast on the 13th day of development?

A

characterised by appearance of villous structures.
• Cells of the cytotrophoblast proliferate locally & penetrate into the syncytiotrophoblast, forming cellular
columns known as (Primary chorionic villi), which are surrounded by trophoblastic lacunae.

43
Q

what happens with regards to the cavities on the 8th day of development?

A

the amniotic cavity starts to be formed within the epiblast.
• Epiblast cells adjacent to the cytotrophoblast are called
amnioblasts.

44
Q

what happens with regards to the cavities on the 9th and 10th day of development?
(long answer)

A

The amniotic cavity become larger.
• The primitive yolk sac cavity
(exocoelomic cavity) starts to be formed as follows:
- Cells from the hypoblast grow down to line the inner surface of the cytotrophoblast forming a thin membrane called Hauser’s membrane (exocoelomic membrane).
- The primitive yolk sac cavity replaces the cavity of the blastocele.

45
Q

what happens with regards to the cavities on the 11th and 11th day of development?
(long answer)

A

The amniotic cavity becomes larger.
• The yolk sac shows no definite changes.
• The extraembryonic coelom, or chorionic cavity develops.
- Growth of the bilaminar disc is relatively slow compared
with the trophoblast.
- Cells of the endometrium, meanwhile, become
polyhedral & loaded with glycogen & lipids; intercellular
spaces are filled with extravasate & the tissue is edematous.
-These changes, known as the decidua reaction.

46
Q

what happens with regards to the cavities on the 13th day of development?
(long answer)

A

Amniotic cavity: no major changes.
- New generation of cells fromhypoblast line the primary yolk sac to form the secondary or definitive sac yolk sac.
- Pinching off a large part of the secondary yolk sac with marked reduction in its size.
-The extraembryonic coelom expands & forms a large cavity, the chorionic cavity.
The only place where extraembryonic mesoderm
traverses the chorionic cavity is in the connecting stalk.
- With development of blood vessels, the stalk becomes
the umbilical cord.
-The extraembryonic mesoderm lining the inside of the
cytotrophoblast is then known as the chorionic plate.

47
Q

why does occasional bleeding happen on around the 13th day ?

A

bleeding at the implantation site caused by increased blood flow into lacunar spaces.

48
Q

what is Gastrulation and during which week does it happen ?

A

the process that establishes the three germ layers (ectoderm, mesoderm, & endoderm)
it happens in the third week

49
Q

what is the Notochord formation during which week does it happen ?

A

it is the temporary axial skeleton of the embryonic disc.

it happens in the third week

50
Q

what 2 things happen during the third week ?

A

Development of the embryonic disc

Development of the trophoblast (Chorion)

51
Q

what happens during gastrulation ?

A

formation of the primitive streak & primitive node on the surface of the epiblast.

52
Q

what is the primitive streak ?

A

a narrow groove with slightly bulging regions on either side formed in the midline of the embryonic disc

53
Q

what is the primitive node?

A

a round bulge located at cephalic end of the streak, with middle depression known as the primitive pit.

54
Q

what is Invagination?

A

Cells of the epiblast migrate toward the groove of the streak & they detach from epiblast & slip beneath it toward the hypoblast, to form:
- Endodermal layer that replace the hypoblast.
• Intraembryonic mesoderm which form the middle layer in the disc.
• Ectoderm layer formed by the remaining cell in the epiblast.
• Thus, the epiblast is the source of all of the germ layers.

55
Q

what is the Cloacal membrane?

A

a small area of fusion between ectoderm & endoderm (no mesoderm).
The cloacal membrane during future development becomes divided into Urogenital membrane & anal membrane.

56
Q

what is the buccopharyngeal membrane?

A

it consists of a small region of tightly adherent ectoderm & endoderm cells (no mesoderm) that represents the future opening of the oral cavity.

57
Q

what is the Notochord?

A

is the temporary axial skeleton of the embryonic disc.

58
Q

how is the notochord formed?

A

it is formed by invagination of solid cord of cells from primitive pit, this process extend cranially in the midline between the ectoderm & endoderm till the
buccopharyngeal membrane.

59
Q

what is the Notochordal canal?

A

primitive pit extends into the process transforming it into a canal.

60
Q

what is Neurenteric canal?

A

It serves as a temporary connection between amniotic cavity & yolk sac cavity.

61
Q

what is the Definitive notochord?

A

notochordal plate becomes folded upon itself forming a solid cord

62
Q

why Is the notochord important?

A
  • Is the temporary axial skeleton of the embryonic disc.
  • During folding its firmness limits the head fold.
  • Vertebral column is formed around the notochord.
63
Q

what happens to the primitive streak in the 4th week ?

A

shows regressive changes, rapidly shrinks & soon disappears.

64
Q

the teratogenic insult is highly sensitive at which week ?

A

the beginning of the 3rd week of development

65
Q

what is the chorion?

A

the wall of the chorionic cavity which is formed at the 12th day of gestation.

66
Q

what are the parts of the chorion?

A

Chorion frondosum

Chorion laeve

67
Q

what is the Chorion laeve?

A

the part that carries degenerating tertiary villi covered

with decidua capsularis.

68
Q

what is the Chorion frondosum?

A

the part that carries well developed tertiary villi that face the decidua basalis, it share in the formation of the placenta.

Embryology (3 decks)

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