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Anatomy Block 1 > Embryology: Germ Layers > Flashcards

Embryology: Germ Layers Flashcards

1
Q

The thickened ridge of epiblast cells; form at the caudal end and extends rostral.

A

Primitive Streak

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2
Q

This “transient structure” is gone by the end of four weeks because gastrulation is complete.

A

Primitive Streak

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3
Q

Cells leave the epiblast layer and start to invaginate, forming a narrow depression in the primitive streak.

A

Primitive Groove

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4
Q

Located at the cranial end of the primitive streak

A

Primitive knot

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5
Q

A small depression within the primitive knot

A

Primitive pit

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6
Q

What is the embryonic connective tissue called that forms the IEM and EEM?

A

Mesenchyme

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7
Q

What type of cells are the “buttery cells”?

A

Mesenchymeal

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8
Q

Where is the site of gastrulation?

A

Primitive streak

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9
Q

This structure gives rigidity and serves as a basis for the development of the axial skeleton.

A

Notochord

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10
Q

The cellular rod that defines the primordial axis of the embryo.

A

Notochord

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11
Q

These three germ layers arise from the epiblast:

A
  1. ectoderm
  2. intraembryonic mesodem (IEM)
  3. endoderm
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12
Q

Another term for the “axial mesoderm” - where medial migration occurs:

A

Notochord

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13
Q

The most rostral migration creates this.

A

Prochordal mesoderm

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14
Q

This will eventually give rise to the heart

A

Prochordal mesoderm

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15
Q

Lateral migration forms the following 3 types of mesoderm:

A
  • Paraxial mesoderrm –> somites
  • Intermediate mesoderm —> nephrogenic
  • Lateral plate mesoderm —> parietal and visceral mesoderm
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16
Q

This forms as a transitory means of communication between the amniotic and yolk sac cavities during the formation of the notochord.

A

The “bizarre” neurenteric canal

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17
Q

What can be formed if the neurenteric canal is not present during notochord formation?

A

Neuroenteric Cysts

(A neurenteric cyst is a type of foregut duplication cyst, associated either with vertebral abnormalities or with the central nervous system. They are usually classified as spinal or intra-cranial.)

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18
Q

True or False: The primitive streak is a transient structure?

A

TRUE - It will regress around the 4th week of development.

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19
Q

What happens if the primitive streak is persistent?

A

It proliferates through all three germ layers to cause a Sacrococcygeal Teratoma

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20
Q

What is a Sacrococcygeal Teratoma?

A

An embryonic tumor that contains all 3 cells types and can develop tissue within itself. Usually benign, but can be very dangerous if metastatic.

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21
Q

True or False: There is migration of the mesoderm where the ectoderm and endoderm meet.

A

False. There is no migration of the mesoderm. This is where we find the oropharyngeal membrane and cloacal membrane.

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22
Q

This is where ectoderm and endoderm meet and fuse at the rostral end. This eventually becomes the mouth.

A

Oropharyngeal membrane

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23
Q

This is where ectoderm and endoderm meet and fuse at the caudal end. This eventually becomes the anus.

A

Cloacal membrane

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24
Q

The diverticulum (out-pocketing) of endoderm located on the caudal end; eventually will become the uracus of the bladder.

A

Allantois

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25
Q

What is “neurulation”?

A

The induction of the neural plate.

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26
Q

The thickened region that is formed when the notochord induces the overlying embryonic ectoderm to thicken and fold inward.

A

Neural Plate

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27
Q

Roles of the notochord in the embryo include:

A
  • serves as a primary spinal column
  • induces neural plate: neural folds, neural groove
  • formation of the neural tube (by cavitation)
  • formation of the neural crest
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28
Q

The invagination of the nerual plate along the central axis; median, longitudinal

A

Neural groove

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29
Q

The invaginated part of the neural plate

A

Neural folds

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30
Q

First sign of brain development occurs here.

A

Neural folds.

*the two opposite sides of the neural folds move together y the end of the 3rd week and begin to fuse

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31
Q

When the neural folds become fully fused:

A

The neural tube forms

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32
Q

Eventually, the neural tube becomes this.

A

Neural Tube

33
Q

What layer gives rise to the neural tube/crest?

A

Ectoderm

34
Q

The neural tube is composed of what?

A

Differentiated epiblast cells.

35
Q

What is the neural fold composed of?

A

Differentiated epiblast cells.

36
Q

To what does the neural crest eventually give rise?

A

PNS.

37
Q

What does the neural tube eventually become?

A

CNS

38
Q

This is also called the embryonic mesoderm.

A

Intraembryonic Mesoderm (IEM)

39
Q

A layer of loose connective tissue between the epiblast of the amniotic cavity and the true ectoderm that lines the top of the yolk sac; formed by mesenchymal cell

A

Intraembryonic Mesoderm (IEM)

40
Q

Cells from the yolk sac endoderm that form a layer of loosely arranged connective tissue that surrounds the amnion and yolk sac. Later, formed by cells that arise from the primitive streak.

A

Extraembryonic Mesoderm (EEM)

41
Q

This releases sonic hedgehog which leads to the induction of the neural plate, neural folds, and the neural groove.

A

Notochord (AKA Axial Mesoderm)

42
Q

This is formed by the medial migration of the IEM

A

Axial mesoderm (Notochord)

43
Q

The area of mesoderm that forms on either side of the neural tube.

A

Paraxial mesoderm

44
Q

This layer of mesoderm differentiates into somites that will eventually form the support structures of the spine.

A

Paraxial Mesoderm

45
Q

This “nephrogenic” layer of the mesoderm eventually gives rise to the urogenital system.

A

Imtermediate mesoderm

46
Q

Layer of mesoderm that will eventually give rise to the linings of the body cavities.

A

Lateral plate of the mesoderm

47
Q

After the formation of the intraembryonic coelom, the dorsal portion of the plate is called the _______ mesoderm and the ventral portion is called the _______ or _______ mesoderm.

A

After the formation of the intraembryonic coelom, the dorsal portion of the plate is called the SOMATIC mesoderm and the ventral portion is called the SPLANCHNIC or VISCERAL mesoderm.

48
Q

What is located in front of the notochord and therefore is the most rostral migration of the IEM?

A

Prochordal Mesoderm

*It is rostral to the oropharyngeal membrane. The splanchnic prochordal mesoderm forms angiogenic cells that will go on to form the inner lining of the heart.

49
Q

What happens if there is a persistent neuropore on the rostral end?

A

Brain formation is affected, resulting in anaencephaly (no brain) or exencephaly (brain outside the head)

50
Q

What happens if there is a persistent neuropore on the caudal end?

A

Spina bifida

  • occulta –> benign
  • cystica –> spinal cord that doesn’t form all the way
51
Q

What is true endoderm formed by?

A

Epiblast

52
Q

Formation of the CNS is induced by:

A

Diffusible signals of the notochord

53
Q

What layer of the lateral plate mesoderm is on the dorsal half?

A

Somatic (parietal) layer

54
Q

What layer of the lateral plate mesoderm is on the ventral half?

A

Splanchnic (visceral) layer

55
Q

The splanchnic layer of the lateral plate mesoderm gives rise to the:

A

visceral linings of body cavities

*Ventral = Visceral

56
Q

The somatic layers of the lateral plate mesoderm give rise to the:

A

parietal linings of the body cavities

57
Q

True or false: Spina Bifida can only occur on the most caudal portion of the spinal cord.

A

FALSE. It can occur anywhere along the spinal cord.

58
Q

These are formed when the paraxial mesoderm differentiate; will eventually give rise to the axial skeleton and associated musculature and adjacent dermis.

A

Somites

59
Q

The horseshoe-shaped tube that splits the rostral lateral plate mesoderm into dorsal and ventral halves. It is open on both ends to the chorionic cavity.

A

Intraembryonic coelom

60
Q

Vessel-forming cells that rise from the splanchnic prochordal mesoderm.

A

Angiogenic cells

61
Q

Angiogenesis

A

Sprouting new blood vessels from existing vessels

62
Q

Vasculogenesis

A

Formation of new blood vessels

63
Q

Two hollow tubes formed from the splanchnic (ventral) prochordal mesoderm; eventually form the lining of the heart.

A

Endocardial heart tubes

64
Q

Formed from rostral prochordal mesoderm; will eventually form the diaphragm

A

Septum transversum

65
Q

What are four major derivatives of the ectoderm?

A
  • The other rapping of the body (epidermis); includes hair, skin, nails, mammary glands, etc.
  • Nervous system (CNS and PNS)
  • Sensory epithelia of ears, nose, and eye
  • Gives rise to bronchial arches
66
Q

The process whereby the differentiation of one group of cells (or one tissue) is controlled by the influence of a second group of cells (or a second tissue)

A

Induction

67
Q

The four main types of induction:

A
  1. Diffusion
  2. Deposition
  3. Contact-mediated
  4. Reciprocal Induction
68
Q

What does cavitation of the lateral plate of the mesoderm form?

A

The intraembryonic coelom (aka the “primitive body cavity”)

69
Q

What is the “primitive body cavity”?

A

The intraembryonic coelom

70
Q

What does the intraembryonic coelom eventually form?

A

The lining of the body cavities (via the somatic and splanchnic mesoderms)

71
Q

When the primitive body cavity (the IEC) forms, which cavity will it communicate with?

A

Chorionic cavity

72
Q

The septum transversum originally forms in front of the IEC and will eventually give rise to what?

A

The diaphragm.

73
Q

Ventral prochordal mesoderm =

A

splanchnic

74
Q

The neural tube is covered by this.

A

Ectoderm.

75
Q

What is gastrulation?

A

The conversion of the bilaminar embryo to a trilaminar embryo

76
Q

What is the first step in conversion of the bilaminar embryo to trilaminar embryo?

A

The formation of the primitive streak.

77
Q

What is the clinical significance of the primitive streak?

A

It actively produces cells that become the IEM and EEM layers

78
Q

What does the neural tube eventually become?

A

CNS

79
Q

What are the likely origins of Neuroenteric cysts?

A

failure of the notochord to completely separate from the foregut during the third week of embryogenesis.

Anatomy Block 1 (6 decks)

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