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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
What is "neurulation"?
The induction of the neural plate.
26
The thickened region that is formed when the notochord induces the overlying embryonic ectoderm to thicken and fold inward.
Neural Plate
27
Roles of the notochord in the embryo include:
- 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
28
The invagination of the nerual plate along the central axis; median, longitudinal
Neural groove
29
The invaginated part of the neural plate
Neural folds
30
First sign of brain development occurs here.
Neural folds. *the two opposite sides of the neural folds move together y the end of the 3rd week and begin to fuse
31
When the neural folds become fully fused:
The neural tube forms
32
Eventually, the neural tube becomes this.
Neural Tube
33
What layer gives rise to the neural tube/crest?
Ectoderm
34
The neural tube is composed of what?
Differentiated epiblast cells.
35
What is the neural fold composed of?
Differentiated epiblast cells.
36
To what does the neural crest eventually give rise?
PNS.
37
What does the neural tube eventually become?
CNS
38
This is also called the embryonic mesoderm.
Intraembryonic Mesoderm (IEM)
39
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
Intraembryonic Mesoderm (IEM)
40
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.
Extraembryonic Mesoderm (EEM)
41
This releases sonic hedgehog which leads to the induction of the neural plate, neural folds, and the neural groove.
Notochord (AKA Axial Mesoderm)
42
This is formed by the medial migration of the IEM
Axial mesoderm (Notochord)
43
The area of mesoderm that forms on either side of the neural tube.
Paraxial mesoderm
44
This layer of mesoderm differentiates into somites that will eventually form the support structures of the spine.
Paraxial Mesoderm
45
This "nephrogenic" layer of the mesoderm eventually gives rise to the urogenital system.
Imtermediate mesoderm
46
Layer of mesoderm that will eventually give rise to the linings of the body cavities.
Lateral plate of the mesoderm
47
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.
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
What is located in front of the notochord and therefore is the most rostral migration of the IEM?
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
What happens if there is a persistent neuropore on the rostral end?
Brain formation is affected, resulting in anaencephaly (no brain) or exencephaly (brain outside the head)
50
What happens if there is a persistent neuropore on the caudal end?
Spina bifida - occulta --> benign - cystica --> spinal cord that doesn't form all the way
51
What is true endoderm formed by?
Epiblast
52
Formation of the CNS is induced by:
Diffusible signals of the notochord
53
What layer of the lateral plate mesoderm is on the dorsal half?
Somatic (parietal) layer
54
What layer of the lateral plate mesoderm is on the ventral half?
Splanchnic (visceral) layer
55
The splanchnic layer of the lateral plate mesoderm gives rise to the:
visceral linings of body cavities *Ventral = Visceral
56
The somatic layers of the lateral plate mesoderm give rise to the:
parietal linings of the body cavities
57
True or false: Spina Bifida can only occur on the most caudal portion of the spinal cord.
FALSE. It can occur anywhere along the spinal cord.
58
These are formed when the paraxial mesoderm differentiate; will eventually give rise to the axial skeleton and associated musculature and adjacent dermis.
Somites
59
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.
Intraembryonic coelom
60
Vessel-forming cells that rise from the splanchnic prochordal mesoderm.
Angiogenic cells
61
Angiogenesis
Sprouting new blood vessels from existing vessels
62
Vasculogenesis
Formation of new blood vessels
63
Two hollow tubes formed from the splanchnic (ventral) prochordal mesoderm; eventually form the lining of the heart.
Endocardial heart tubes
64
Formed from rostral prochordal mesoderm; will eventually form the diaphragm
Septum transversum
65
What are four major derivatives of the ectoderm?
- 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
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)
Induction
67
The four main types of induction:
1. Diffusion 2. Deposition 3. Contact-mediated 4. Reciprocal Induction
68
What does cavitation of the lateral plate of the mesoderm form?
The intraembryonic coelom (aka the "primitive body cavity")
69
What is the "primitive body cavity"?
The intraembryonic coelom
70
What does the intraembryonic coelom eventually form?
The lining of the body cavities (via the somatic and splanchnic mesoderms)
71
When the primitive body cavity (the IEC) forms, which cavity will it communicate with?
Chorionic cavity
72
The septum transversum originally forms in front of the IEC and will eventually give rise to what?
The diaphragm.
73
Ventral prochordal mesoderm =
splanchnic
74
The neural tube is covered by this.
Ectoderm.
75
What is gastrulation?
The conversion of the bilaminar embryo to a trilaminar embryo
76
What is the first step in conversion of the bilaminar embryo to trilaminar embryo?
The formation of the primitive streak.
77
What is the clinical significance of the primitive streak?
It actively produces cells that become the IEM and EEM layers
78
What does the neural tube eventually become?
CNS
79
What are the likely origins of Neuroenteric cysts?
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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