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EMBRYOLOGY > Trilaminar Germ Disc > Flashcards

Trilaminar Germ Disc Flashcards

1
Q

It is the process that establishes all 💡three germ layers (ectoderm, mesoderm, and endoderm) in the embryo.

A

GASTRULATION

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2
Q

It is the 💡most characteristic event occurring during the 💡third week of gestation.

A

GASTRULATION

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3
Q

Gastrulation begins with formation of the __ on the surface of the epiblast.

It is a place where cells of the epiblast migrate

A

Primitive streak

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4
Q

Initially, the streak is vaguely defined, but in a __, it is clearly visible as a narrow groove with slightly bulging regions on either side.

A

15- to 16-day embryo

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5
Q

It is the 💡cephalic end of the primitive streak.

Consists of a slightly elevated area surrounding the small 💡primitive pit

A

Primitive node

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6
Q

This growth factor controls 💡cell migration a by 💡 down regulating E-cadherin and controls 💡 cell specification into the mesoderm by regulating 💡 BRACHYURY (T) expression.

It induces the expression of 💡NODAL

A

Fibroblast growth factor 8 (FGF8)

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7
Q

It is a protein that normally 💡binds epiblast cells together.

A

E-cadherin

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8
Q

Once the cells have invaginated, some 💡displace the hypoblast, creating the embryonic __.

A

Endoderm

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9
Q

Once the cells have invaginated, others come to 💡lie between the epiblast and 💡newly created endoderm to form __.

A

Mesoderm

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10
Q

Cells remaining in the epiblast then form __.

A

Ectoderm

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11
Q

It is the source of all three germ layers through the process of gastrulation.

A

Epiblast

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12
Q

It is important for induction of the 💡forebrain.

It is an area just 💡caudal to the oropharyngeal membrane.

It is formed by the 💡mesoderm cells.

A

Prechordal plate

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13
Q

It consists of a small región of 💡tightly adherent ectoderm and endoderm cells that represents the future opening of the 💡oral cavity.

A

Oropharyngeal membrane

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14
Q

These cells invaginating in the 💡primitive node move forward cranially in the midline until they reach the 💡prechordal plate

A

Prenotochordal cells

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15
Q

These 💡prenotochordal cells become intercalated in the 💡hypoblast so that for a short time, the midline of the embryo consists of two cell layers that form the __.

A

Notochordal plate

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16
Q

These are 💡solid cord of cells formed when 💡cells of the notochordal plate proliferate and detach from the endoderm.

It underlies the 💡neural tube and is a 💡signaling center for inducing the 💡axial skeleton.

A

Definitive notochord

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17
Q

Because elongation of the notochord is a dynamic process, the __ forms first, and __ are added as the primitive streak assiunes a more caudal position.

A

Cranial end

Caudal regions

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18
Q

It 💡temporarily connects the amniotic and yolk sac cavities at the point where the pit forms an indentation in the epiblast.

A

Neurenteric canal

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19
Q

It is formed at the 💡caudal end of the embryonic disc

CSimilar in structure to the oropharyngeal membrane.

It consists of 💡tightly adherent ectoderm and endoderm cells with 💡no intervening mesoderm.

A

Cloacal membrane

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20
Q

It appears around the 💡16th day of development when the 💡cloacal membrane appears, the 💡posterior wall of the yolk sac forms a 💡small diverticulum that extends into the connecting stalk.

A

Allantoenteric diverticulum or Allantois

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21
Q

Establishment of the __, occurs early in embryogenesis and is probably initiated dur- ing the mórula stage of development with the A-P and D-V axes specified prior to the L-R.

A

Body axes, anterior- posterior (A-P; craniocaudal), dorso-ventral(D-V), and left-right (L-R)

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22
Q

At this bilaminar disc stage, cells in the __ express genes essential for head formation.

A

Anterior visceral endoderm (AVE)

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23
Q

These are genes essential for head formation;

A

Transcription factors:
OTX2
LIMl
HESXl

Secreted factors:
Cerberus and leftyl (members of the TGF-beta family)

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24
Q

These are secreted factors gene which 💡inhibit nodal activity.

A

Cerberus and Leftyl

25
Q

It is a gene that establishes and maintains the 💡primitive streak.

It up regulates a number of genes responsible for formation of 💡dorsal and ventral mesoderm and 💡head and tail structures.

A

NODAL

26
Q

It is secreted throughout the 💡embryonic disc.

Together with FGF, mesoderm will be 💡ventralized to contribute to kidneys (intermedíate mesoderm), blood, and body wall mesoderm (lateral píate mesoderm).

A

Bone Morphogenetic Protein 4 (BMP4)

27
Q

These are genes that 💡antagonize the activity of BMP4.

As a result, cranial mesoderm is. 💡 dorsalized into notochord, somites, and somitomeres

They are important in 💡neural induction in the cranial región.

A

CHORDIN (activated by the transcription factor GOOSECOID)

Noggin

Follistatin

28
Q

It maintains the 💡node and later 💡induces regional specificity in the forebrain and midbrain areas.

A

HNF-3B

29
Q

What will happen to the embryo without HNP-3B?

A

The embryos fail to gastrulate properly and lack forebrain and midbrain structures.

30
Q

It is a gene that controls the regulation of 💡dorsal mesoderm formation in 💡middle and caudal regions of the embryo.

This gene is essential for 💡cell migration through the primitive streak.

A

BRACHYURY (T) gene

31
Q

Without BRACHYURY (T) gene, what will happen to the emryo?

A

There will be shortening of the embryonic axis (caudal dysgenesis).

32
Q

NODAL expression is then restricted to the left side of the embryo by the accumulation of __ on the left side.

It activate expression of the transcription factor 💡MAD3

A

SEROTONIN (5-HT)

33
Q

It is a transcription factor that 💡restricts NODAL expression to the left side of the primitive node

A

MAD3

34
Q

These are 💡midline genes that are involved in establishing the midline but also 💡prevent NODAL expression from crossing over to the right side.

A

SONIC HEDGEHOG (SHH), LEFTYl, and ZIC3

35
Q

It is a gene on the 💡X chromosome that codes for a 💡zinc finger transcription factor

A

ZIC3

36
Q

Nodal protein in the left lateral plate mesoderm initiates a signaling cascade to upregulate 💡PITX2

A

LEFTY2

37
Q

It is a 💡homeobox-containing transcription factor that is a 💡“master gene” responsible for 💡 establishing left-sidedness, and its expression is repeated on the left side of the heart, stomach, and gut primordia as these organs are assuming their normal asymmetrical body positions.

A

PITX2

38
Q

If the PITX2 is expressed 💡ectopically (e.g., on the right side), this abnormal expression results in __.

A

Laterality defects (situs inversus and dextrocardia)

39
Q

Cells that ingress through the cranial región of the node become __.

A

prechordal plate and notochord

40
Q

Those migrating at the 💡lateral edges of the node and from the 💡cranial end of the streak become __.

A

paraxíal mesoderm

41
Q

Cells migrating through the 💡midstreak región become __.

A

intermedíate mesoderm

42
Q

Those migrating through the 💡more caudal part of the streak form __.

A

lateral plate mesoderm

43
Q

Cells migrating through the 💡caudal most part of the streak contribute to __.

A

extraembryonic mesoderm

44
Q

It consist of a 💡cytotrophoblastic core covered by a 💡syncytial layer

A

Primary Villi

45
Q

It is formed when 💡mesodermal cells penetrate the core of primary villi and grow toward the decidua.

A

Secondary villi

46
Q

By the end of the third week, mesodermal cells in the core of the villus begin to differentiate into 💡blood cells and small blood vessels, forming the 💡villous capillary system

A

Tertiary Villi

Definitive Placentla Villi

47
Q

When the heart begins to beat in the __ of development, the villous system is ready to supply the embryo proper with essential nutrients and oxygen.

A

Fourth week

48
Q

It is formed when 💡cytotrophoblastic cells establish contact with similar extensions of 💡 neighboring villous stems.

This shell gradually 💡 surrounds the trophoblast entirely and 💡 attaches the chorionic sac firmly to the maternal endometrial tissue

A

Outer cytotrophoblast shell

49
Q

It is a 💡villi that extend from the 💡chorionic plate to the 💡decidua basalis.

A

Stem or anchoring villi

50
Q

It is the part of the 💡endometrium where the 💡placenta will form

A

Decidua basalis (decidual plate)

51
Q

Those that branch from the sides of stem villi are __, through which 💡exchange of nutrients and other factors will occur.

A

free (terminal) villi

52
Q

● Deficiency of the 💡midline in craniofacial structures
● Caused by 💡high doses of alcohol at this stage
○ Alcohol kills cells in the anterior midline of
the germ disc
○ The face would be affected 💡(cyclops)
because it affects the formation of the
eye and the brain.

A

Holoprosencephaly

53
Q

● 💡Lower extremities are fused together, like a mermaid

● They do not survive the first few months of life because of severe genetic defect

A

Sirenomelia (Caudal Dysgenesis)

54
Q

● Tumors formed by 💡clusters of pluripotent cells that are 💡remnants of the primitive streak persisting in the sacrococcygeal region
● 💡Most common tumor in newborns
● Commonly 💡contain tissues derived from all three germ layers
○ Includes hair structures, sebaceous structures, teeth, and bone

A

Sacrococcygeal teratomas

55
Q

💡Normal positioning of the internal organs

A

Situs solitus

56
Q

It is a condition where the positioning of all organs is 💡reversed in a mirror image arrangement

A

Situs inversus

57
Q

Laterality defects occur because of a failure to

properly establish the __.

A

L-R axis

58
Q

It is an arrangement of internal organs somewhere 💡between situs solitus and situs inversus
● Unlike situs inversus, the abnormal arrangement of organs in heterotaxy often causes serious health
problems.

A

Situs ambiguus (Heterotaxy)

EMBRYOLOGY (7 decks)

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