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Histology & Embryology > 3rd week of development (exam 2) > Flashcards

3rd week of development (exam 2) Flashcards

1
Q

What week of development is this?
-rapid development
-appearance of primitive streak
-development of notochord (develops into NS, 1st system developed)
-differentiation of 3 germ layers “germination”

A

3rd week of development

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2
Q

The 3rd week of development coincides with the week after the 1st missed period, which is ____ weeks after the 1st day of the last normal menstrual period

A

5

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3
Q

What is the 1st major event in 3rd week of development?

A

gastrulation

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4
Q

How does gastrulation begin?

A

the formation of a longitudinal midline (groove) structure, called the primitive streak

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5
Q

Where does the primitive streak begin and end?

A

starts in the epiblast as a small depression and then ends at the caudal end of the embryonic disc (embryo)

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6
Q

What is gastrulation?

A

a formative process where the 3 germ layers (precursors of all embryonic tissues) and the axial orientation are established in embryo

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7
Q

Gastrulation is the beginning of _________________ (development of body form) and is the most significant event occurring during the 3rd week. The embryo is referred to as a gastrula

A

morphogenesis

note: morphology is the study of shapes and structures

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8
Q

The first morphological sign of gastrulation is the formation of the….

A

primitive streak

note: the primitive streak defines for the first time with all major body axes. These consist of the caudal (or head-tail) axis, and the dorsal-ventral (or back-belly) axis and the left-right axis

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9
Q

On about day 15 of development, a thickening containing a midline groove forms along the midsagittal plane of the embryonic disc, which has now assumed as an….

A

oval shape

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10
Q

The thickening of cells, called the _________________, elongates to occupy about 1/2 of the length of the embryonic disc, and the groove is called the _____________________ (indentation), becomes deeper and more defined

A

primitive streak, primitive groove

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11
Q

The cranial end of the primitive streak is expanded into a structure called the _______________. It contains a depression called the _________________

A

primitive node, primitive pit

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12
Q

The primitive streak forms at the caudal midline of the ________________. Thus, the cranial-caudal axis can be identified. Formation of the primitive streak also heralds the beginning of gastrulation

A

embryonic disc

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13
Q

The primitive streak, occupies ______% of the length of the embryonic disc

A

50

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14
Q

During gastrulation, epiblast cells move toward the primitive streak, enter the primitive streak, and then migrate away from the primitive streak as individual cells. This is called…..

A

ingression

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15
Q

On day _____, epiblast cells lateral to the primitive streak begin to move into the primitive streak, where they undergo an epithelial-to-mesenchymal transition and loose cell contact

A

16

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16
Q

During gastrulation, epiblast cells move toward the primitive streak, enter the primitive streak, and then migrate away from the primitive streak as individual cells. This is called ingression. On day 16, epiblast cells lateral to the primitive streak begin to move into the primitive streak, where they undergo an epithelial-to-mesenchymal transition and loose cell contact. The collective movement of cells through the primitive streak and into the interior of the embryo form the 3 primary germ layers constitutes…..

A

gastrulation

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17
Q

The 1st ingressing epiblast cells invade the hypoblast and displace its cells so that the hypoblast eventually is completely replaced by a new layer of cells. This is called the…..

A

definitive endoderm (this happens medially to laterally)

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18
Q

Some epiblast cells migrating through the primitive streak diverge into the space between epiblast and nascent definitive endoderm to form a 3rd germ layer - the …..

A

intraembryonic mesoderm

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19
Q

Some epiblast cells migrating through the primitive streak diverge into the space between epiblast and nascent definitive endoderm to form a 3rd germ layer- the intraembryonic mesoderm (inside embryo). These cells migrate bilaterally from the primitive streak initially and form a loose mat of cells between epiblast and endoderm. The mat reorganizes to form 4 main subdivisions of intraembryonic mesoderm. What are these 4 subdivisions called?

A

1) cardiogenic mesoderm
2) paraxial mesoderm
3) intermediate mesoderm (also called nephrotome)
4) lateral plate mesoderm

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20
Q

The 5th population of mesodermal cells migrate cranially from the primitive node at the midline to form a thick-walled midline tube called the….

A

notochordal process (will become notochord soon)

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21
Q

During gastrulation, epiblast will replace hypoblast to become….

Test q

A

endoderm (and epiblast will also replace itself to become ectoderm)

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22
Q

2 faint depressions form in the ectoderm: one at the cranial end of the embryo and the other at the caudal end behind the primitive streak. The ectoderm (top layer) in these areas fuses tightly with the underlying endoderm (bottom layer), excluding the mesoderm and forming bilaminar membranes. The cranial membrane is called the _________________ membrane, and the caudal membrane is the ____________ membrane.

test q!

A

oropharyngeal, cloacal

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23
Q

The oropharyngeal and cloacal membranes later become the blind ends of the….

A

gut tube

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24
Q

T/F: once formation of the definitive endoderm and intraembryonic mesoderm is complete, the epiblast cells no longer move

A

true!

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25
Q

The remaining epiblast after forming the germ layers is now the _____________, which quickly differentiates into the central neural plate and the peripheral surface ectoderm

A

ectoderm

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26
Q

Eventually, the process of gastrulation is complete. At that time- formation of the 3 definitive germ layers of the trilaminar embryonic disc- ectoderm, mesoderm, and endoderm will be complete throughout the length of the disc. ALL 3 germ layers derive from ___________ during gastrulation (referred as gastrula)

A

epiblast

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27
Q

Morphogenetic changes (shape-generating events) occur in each of the germ layers to form the primitive organs rudiments. These are often referred to as…

A

ectodermal, mesodermal, and endodermal derivatives (will eventually become organs with other tissues- remember multiple tissues make an organ)

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28
Q

Formation of the notochord begins with a cranial midline extension form the primitive node, a hollow tube- the…

A

notochordal process

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29
Q

When the notochordal process is completely formed, several transformations take place to convert it from a hollow tube, to a flattened plate, to a….

A

solid rod

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30
Q

The floor of the hollow tube fuses with the underlying endoderm and the 2 layers break down leaving a flattened notochordal _________

A

plate

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31
Q

The floor of the hollow tube fuses with the underlying endoderm and the 2 layers break down leaving a flattened notochordal plate. The notochordal plate them completely detaches from the endoderm, its free ends fuse as it rolls into the containing space between the ectoderm and endoderm, changing into a solid rod called the….

A

notochord (notochord formation takes about 4-5 days)

32
Q

What is the major inductor of embryological development?

A

the notochord

33
Q

Later in development, rudiments of the vertebral bodies coalesce around the….

A

notochord

34
Q

The notochord forms the ______________ at the center of the vertebral discs. This is true in the embryo, fetus, and in young children, but is replaced in adults. The notochord plays many important inductive and patterning roles in early development

A

nucleus pulposus

35
Q

The developing notochord induces the overlying embryonic ectoderm to thicken and form the….

A

neural plate

36
Q

The paraxial mesoderm flanks the….

A

notochord

37
Q

In the future head region, the mesoderm forms bands of cells that remain ________________ as the head mesoderm

A

unsegmented/uniform

38
Q

The mesoderm becomes more dispersed with development to loosely fill the developing head as the head mesenchyme. The head mesenchyme is derived from both head mesoderm and….

A

ectodermal neural crest cells

39
Q

The head mesoderm eventually give rise to the….

A

striated muscles of the face, jaw, and throat

40
Q

The head mesoderm eventually give rise to the striated muscles of the face, jaw, and throat. These muscles differentiate within the segmental _________________________, which develop on either side of the pharynx

A

pharyngeal arches

41
Q

In the future trunk region, the paraxial mesoderm also forms bands of cells, these bands soon segment into ____________, block-like condensations of mesoderm

A

somites

42
Q

What is the hallmark of making vertebrae?

A

somites

43
Q

In addition to the notochord, some cells derived form the primitive node form the….

A

paraxial mesoderm

44
Q

In addition to the notochord, some cells derived form the primitive node form the paraxial mesoderm. Close to the primitive node, this cell population appears as a thick, longitudinal column of cells. Each column is continuous laterally with the _____________ mesoderm, which gradually thins into a layer of ___________ mesoderm

A

intermediate, lateral

45
Q

Toward the end of the 3rd week, the paraxial mesoderm differentiates, condenses, and begins to divide into paired cuboidal bodies, the somites, which form in a craniocaudal sequences. These blocks of mesoderm are located on….

A

each side of the developing neural tube

46
Q

The size and shape of the somites are determined by….

A

cell-cell interactions

47
Q

By the end of the 5th week, ___________ pairs of somites are present

A

42-44 (on L/R side)

48
Q

The first pair of somites forms/condenses on about day _____ at the head-trunk border. The remainder form in cranial-caudal progression at a rate of about ______ a day

A

20, 3-4 (pairs)

49
Q

What do somites give rise to?

A

-most of the axial skeleton including the vertebral column and part of the occipital bone of the skull
-the voluntary musculature of the neck, body walls, and limbs
-the dermis of the body

50
Q

T/F: formation and segregation of somites are of major importance in organization of the body structure

A

TRUE

51
Q

When somites first from mesoderm, they exist as a ______ of mesoderm

A

ball

52
Q

Cells in the ventral and medial walls of the somite lose their epithelial characteristics and move their position to surround the neural tube and notochord. Collectively, these cells form the ______________ that will differentiate into the vertebrae and ribs

A

sclerotome

53
Q

Cells at the dorsomedial and ventrolateral regions differentiate into muscle precursor cells- ?

A

myotome

54
Q

Cells that remain between sclerotome and myotome will form the….

A

dermatome

55
Q

In addition to the notochord and paraxial mesoderm, both of which form in the head and trunk, 2 other subdivisions of mesoderm form in the trunk only:

A

intermediate and lateral plate mesoderm

56
Q

The notochord forms and then what? List each mesoderm in order

A

-notochord
-paraxial mesoderm
-intermediate mesoderm
-lateral plate mesoderm (splanchnic and somatic mesoderm)

all of these are in a “line” above the endoderm from medially to laterally

so notochord in center, paraxial on left/right of notochord, and so on

57
Q

Immediately lateral to somites is the intermediate mesoderm. This produces parts of what systems?

A

urinary and genital system

58
Q

Lateral to the intermediate mesoderm is a flattened sheet called the…

A

lateral plate mesoderm

59
Q

The lateral plate mesoderm splits into 2 layers. What are they?

A

1) ventral layer associated w/ the endoderm also known as splanchnic mesoderm which becomes visceral structures
2) dorsal layer associated with the ectoderm known as somatic mesoderm forms the inner lining of the body wall

60
Q

The splanchnic layer forms the __________, and the somatic layer forms part of the lining of the pericardial cavity

A

heart wall

61
Q

When does the CNS start to form?

A

week 3 of development

62
Q

The ectoderm just above the primitive node thickens to form a _______________. The ectodermal cells thicken to become neuroepithelial cells (________________). The neural plate forms first at the cranial end of the embryo and then differentiates in a cranial to caudal direction

A

neural plate, neuroectoderm

63
Q

The neuroectoderm of the neural plate gives rise to the….

A

CNS

64
Q

On approximately the 18th day of development, the neural plate invaginates along its central axis to form a longitudinal median neural groove. As the groove dips down/gets deeper, the side have neural folds. The folds are more prominent first at the cranial end. The neural folds move together and fuse, converting the neural plate into the….

A

neural tube

65
Q

What is A?

A
66
Q

What is B?

A
67
Q

What is C?

A
68
Q

What is D?

A
69
Q

What is E?

A
70
Q

What is F?

A
71
Q

What is A?

A
72
Q

What is B?

A
73
Q

What is C?

A
74
Q

What is D?

A
75
Q

What is E?

A

Histology & Embryology (21 decks)

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