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Embryology > Chapter 6 > Flashcards

Chapter 6 Flashcards

1
Q
A
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2
Q

The _____, or period of organogenesis, occurs from the third to the eighth weeks of development and is the time when each of the three germ layers, ectoderm, mesoderm, and endoderm, gives rise to a number of specific tissues and organs

A

embryonic period

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3
Q

The embryonic period, or period of ____, occurs from the third to the eighth weeks of development and is the time when each of the three germ layers, ectoderm, mesoderm, and endoderm, gives rise to a number of specific tissues and organs

A

organogenesis

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4
Q

The embryonic period, or period of organogenesis, occurs from the ____ of development and is the time when each of the three germ layers, ectoderm, mesoderm, and endoderm, gives rise to a number of specific tissues and organs

A

third to the eighth weeks

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5
Q

The embryonic period, or period of organogenesis, occurs from the third to the eighth weeks of development and is the time when each of the three germ layers, ___, ____, and _____, gives rise to a number of specific tissues and organs

A

ectoderm, mesoderm, and endoderm

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6
Q

The third to eighth weeks are also cited as the time when the majority of birth defects are induced; prior to this time, any insult to the embryo results in its death and spontaneous abortion. Although this tenet holds true for many insults to normal development, it is important to note that ___ begins late in the first week at the blastocyst stage and that a great variety of birth defects can be attributed to disruptions in cell signaling during specification of the cranial-caudal and left-right axes

A

axis formation

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7
Q

The third to eighth weeks are also cited as the time when the majority of birth defects are induced; prior to this time, any insult to the embryo results in its death and spontaneous abortion. Although this tenet holds true for many insults to normal development, it is important to note that axis formation begins late in the ____ at the blastocyst stage and that a great variety of birth defects can be attributed to disruptions in cell signaling during specification of the cranial-caudal and left-right axes

A

first week

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8
Q

Appearance of the notochord and prechordal mesoderm induces the overlying ectoderm to thicken and form the ____

A

neural plate

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9
Q

Cells of the plate make up the ____, and their induction represents the initial event in the process of neurulation

A

neuroectoderm

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10
Q

Cells of the plate make up the neuroectoderm, and their induction represents the initial event in the process of _____

A

neurulation

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11
Q

Upregulation of fibroblast growth factor (FGF) signaling together with inhibition of the activity of ____, a transforming growth factor-B (TGF-B) family member responsible for ventralizing ectoderm and mesoderm, causes induction of the neural plate

A

bone morphogenetic protein 4 (BMP4)

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11
Q

Upregulation of _____ signaling together with inhibition of the activity of bone morphogenetic protein 4 (BMP4), a transforming growth factor-B (TGF-B) family member responsible for ventralizing ectoderm and mesoderm, causes induction of the neural plate

A

fibroblast growth factor (FGF)

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12
Q

Upregulation of fibroblast growth factor (FGF) signaling together with inhibition of the activity of bone morphogenetic protein 4 (BMP4), a _____ family member responsible for ventralizing ectoderm and mesoderm, causes induction of the neural plate

A

transforming growth factor-B (TGF-B)

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13
Q

FGF signaling probably promotes a neural pathway by an unknown mechanism while it represses BMP transcription and upregulates expression of ___ and ___, which inhibit BMP activity

A

CHORDIN and NOGGIN

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14
Q

Secretion of three other molecules, ____, ____, and _____, inactivates BMP

A

noggin, chordin, and follistatin

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15
Q

Induction of caudal neural plate structures (hindbrain and spinal cord) depends on two secreted proteins, ___ and ___. In addition, retinoic acid (RA) appears to play a role in organizing the cranial-to-caudal axis because it can cause the respecification of cranial segments into more caudal ones by regulating expression of homeobox genes

A

WNT3a and FGF

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15
Q

Induction of caudal neural plate structures (hindbrain and spinal cord) depends on two secreted proteins, WNT3a and FGF. In addition, ____ appears to play a role in organizing the cranial-to-caudal axis because it can cause the respecification of cranial segments into more caudal ones by regulating expression of homeobox genes

A

retinoic acid (RA)

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16
Q

Induction of caudal neural plate structures (hindbrain and spinal cord) depends on two secreted proteins, WNT3a and FGF. In addition, retinoic acid (RA) appears to play a role in organizing the cranial-to-caudal axis because it can cause the respecification of cranial segments into more caudal ones by regulating expression of _____

A

homeobox genes

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17
Q

As the neural plate lengthens, its lateral edges elevate to form ____, and the depressed midregion forms the neural groove

A

neural folds

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18
Q

As the neural plate lengthens, its lateral edges elevate to form neural folds, and the depressed midregion forms the ____. As a result, the neural tube is formed.

A

neural groove

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19
Q

As the neural plate lengthens, its lateral edges elevate to form neural folds, and the depressed midregion forms the neural groove. As a result, the ____ is formed.

A

neural tube

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20
Q

Until fusion is complete, the cephalic and caudal ends of the neural tube communicate with the amniotic cavity by way of the ____ and posterior (caudal) neuropores, respectively

A

anterior (cranial)

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21
Q

Until fusion is complete, the cephalic and caudal ends of the neural tube communicate with the amniotic cavity by way of the anterior (cranial) and ____, respectively

A

posterior (caudal) neuropores

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22
Q

Neurulation is then complete, and the central nervous system is represented by a closed
tubular structure with a narrow caudal portion, the ___, and a much broader cephalic portion characterized by a number of dilations, the brain vesicles

A

spinal cord

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23
Q

Neurulation is then complete, and the central nervous system is represented by a closed
tubular structure with a narrow caudal portion, the spinal cord, and a much broader cephalic portion characterized by a number of dilations, the _____

A

brain vesicles

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24
Q

This cell population, the _____, undergoes an epithelial-to-mesenchymal transition as it leaves the neuroectoderm by active migration and displacement to enter the underlying mesoderm.

A

neural crest cells

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25
Q

This cell population, the neural crest cells, undergoes an _____ as it leaves the neuroectoderm by active migration and displacement to enter the underlying mesoderm.

A

epithelial-to-mesenchymal transition

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26
Q

(____ refers to cells derived from the epiblast and extraembryonic tissues. Mesenchyme refers to loosely organized embryonic connective tissue regardless of origin.)

A

Mesoderm

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27
Q

(Mesoderm refers to cells derived from the epiblast and extraembryonic tissues. ___ refers to loosely organized embryonic connective tissue regardless of origin.)

A

Mesenchyme

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28
Q

Crest cells from the trunk region leave the neuroectoderm ____ of the neural tube and migrate along one of two pathways:
(1) a dorsal pathway through the dermis, where they will enter the ectoderm through holes in the basal lamina to form melanocytes in the skin and hair follicles, and (2) a ventral pathway through the anterior half of each somite to become sensory ganglia, sympathetic and enteric neurons, Schwann cells, and cells of the adrenal medulla

A

after closure

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29
Q

Crest cells from the trunk region leave the neuroectoderm after closure of the neural tube and migrate along one of two pathways:
(1) a dorsal pathway through the dermis, where they will enter the ectoderm through holes in the basal lamina to form ___ in the skin and hair follicles
(2) a ventral pathway through the anterior half of each somite to become sensory ganglia, sympathetic and enteric neurons, Schwann cells, and cells of the adrenal medulla

A

melanocytes

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30
Q

Crest cells from the trunk region leave the neuroectoderm after closure of the neural tube and migrate along one of two pathways:
(1) a dorsal pathway through the dermis, where they will enter the ectoderm through holes in the basal lamina to form melanocytes in the skin and hair follicles, and (2) a ventral pathway through the anterior half of each somite to become ____, ____, ____, and ____

A

sensory ganglia, sympathetic and enteric neurons, Schwann cells, and cells of the adrenal medulla

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31
Q

NCC also form and migrate from cranial neural folds, leaving the neural tube ___ in this region

A

before closure

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32
Q

These cells contribute to the ___ as well as neurons for cranial ganglia, glial cells, melanocytes, and other cell types

A

craniofacial skeleton

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33
Q

These cells contribute to the craniofacial skeleton as well as ____, ____, _____, and other cell types

A

neurons for cranial ganglia, glial cells, melanocytes

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34
Q

NCC are so fundamentally important and contribute to so many organs and tissues that they are sometimes referred to as the ____

A

fourth germ layer

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35
Q

Give the Different neural crest derivatives

A

Connective tissue and bones of the face and skull
Cranial nerve ganglia
C cells of the thyroid gland
Conotruncal septum in the heart
Odontoblasts
Dermis in face and neck
Spinal [dorsal root] ganglia
Sympathetic chain and preaortic ganglia
Parasympathetic ganglia of the gastrointestinal tract
Adrenal medulla
Schwann cells
Glial cells
Meninges [forebrain]
Melanocytes
Smooth muscle cells to blood vessels of the
face and forebrain

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35
Q

They are also involved in at least ____ of all birth defects and many cancers, such as melanomas, neuroblastomas, and others

A

one-third

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36
Q

By the time the neural tube is closed, two bilateral _____, the otic placodes and the lens placodes, become visible in the cephalic region of the embryo

A

ectodermal thickenings

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37
Q

By the time the neural tube is closed, two bilateral ectodermal thickenings, the ____ and the lens placodes, become visible in the cephalic region of the embryo

A

otic placodes

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38
Q

By the time the neural tube is closed, two bilateral ectodermal thickenings, the otic placodes and the _____, become visible in the cephalic region of the embryo

A

lens placodes

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39
Q

During further development, the otic placodes invaginate and form the ___, which will develop into structures needed for hearing and maintenance of equilibrium

A

otic vesicles

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40
Q

At approximately the same time, the ___ these placodes also invaginate and, during the fifth week, form the lenses of the eyes

A

lens placodes

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41
Q

At approximately the same time, the lens placodes appear. These placodes also invaginate and, during the fifth week, form the ____ of the eyes

A

lenses

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42
Q

___ result when neural tube closure fails to occur

A

Neural tube defects [NTDs]

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43
Q

If the neural tube fails to close in the cranial region, then most of the brain fails to form, and the defect is called ___

A

anencephaly

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44
Q

If closure fails anywhere from the cervical region caudally, then the defect is called ___

A

spina bifida

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45
Q

The ___ genes are part of the planar cell polarity pathway that regulates convergent extension, the process that lengthens the neural tube and is necessary for normal closure to occur

A

VANGL

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46
Q

Regardless of the region or country where
NTDs occur, and rates have been reduced significantly following ___ administration

A

folic acid

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47
Q

It is estimated that 50% to 70% of NTDs can be prevented if women take ___ of folic acid daily [the dose present in most multivitamins] beginning 3 months prior to conception and continuing throughout pregnancy

A

400 pg

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48
Q

If a woman has had a child with an NTD or if there is a history of such defects in her family, it is recommended that she take 400 pg of folic acid daily and then ___ per day starting 1 month before she tries to become pregnant and continuing through the first 3 months of pregnancy.

A

4,000 pg

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48
Q

By approximately the 17th day, however, cells close to the midline proliferate and form a thickened plate of tissue known as __

A

paraxial mesoderm

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49
Q

More laterally, the mesoderm layer remains thin and is known as the ___

A

lateral plate

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49
Q

Together, these layers line a newly formed cavity, the ___, which is continuous with the extraembryonic cavity on each side of the embryo.

A

intraembryonic cavity

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50
Q

With the appearance and coalescence of intercellular cavities in the lateral plate, this tissue is divided into two layers:
1. A layer continuous with mesoderm covering the amnion, known as the _____
2. A layer continuous with mesoderm covering the yolk sac, known as the ___

A

somatic or parietal mesoderm layer
splanchnic or visceral mesoderm layer

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51
Q

These segments, known as ___, first appear in the cephalic region of the embryo, and their formation proceeds cephalocaudally.

A

somitomeres

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51
Q

___ connects paraxial and lateral plate mesoderm

A

Intermediate mesoderm

52
Q

In the head region, somitomeres form in association with segmentation of the neural plate into ____ and contribute to mesenchyme in the head

A

neuromeres

53
Q

Formation of segmented somites from un-segmented presomitic (paraxial) mesoderm depends on a____ established by cyclic expression of a number of genes

A

segmentation clock

53
Q

The cyclic genes include members of the ___ and ___ signaling pathways that are expressed in an oscillating pattern in presomitic mesoderm

A

NOTCH and WNT

54
Q

Boundaries for each somite are regulated by retinoic acid (RA) and a combination of ___ and ___

A

FGF8 and WNT3a

54
Q

Boundaries for each somite are regulated by ___ and a combination of FGF8 and WNT3a

A

retinoic acid (RA)

55
Q

RA is expressed at high concentrations cranially and decreases in concentration caudally, whereas the combination of ___ and ___ proteins is expressed at higher concentrations caudally and lower ones cranially

A

FGF8 and WNT3a

56
Q

Number of somites at 20 days

A

1-4

56
Q

Number of somites at 21 days

A

4-7

57
Q

Number of somites at 22 days

A

7-10

57
Q

Number of somites at 24 days

A

13-17

57
Q

Number of somites at 23 days

A

10-13

58
Q

Number of somites at 25 days

A

17-20

58
Q

Number of somites at 26 days

A

20-23

59
Q

Number of somites at 27 days

A

23-26

60
Q

Number of somites at 28 days

A

26-29

61
Q

Number of somites at 30 days

A

34-35

62
Q

When somites first form from presomitic mesoderm, they exist as a ball of mesoderm (fibroblast-like) cells. These cells then undergo a process of ___ and arrange themselves in a donut shape around a small lumen

A

epithelization

63
Q

By the beginning of the fourth week, cells in the ventral and medial walls of the somite lose their epithelial characteristics, become mesenchymal (fibroblast-like) again, and shift their position to surround the neural tube and notochord. Collectively, these cells form the ___ that will differentiate into the vertebrae and ribs

A

sclerotome

64
Q

The secreted protein products of the ____ genes and ___, produced by the notochord and floor plate of the neural tube, induce the ventromedial portion of the somite to become sclerotome

A

NOGGIN - sonic hedgehog (SHH)

64
Q

Hence, each somite forms its own ___ (the tendon cartilage and bone component), its own ___ (providing the segmental muscle component), and its own ___, which forms the dermis of the back

A

sclerotome - myotome - dermatome

65
Q

Once induced, sclerotome cells express the transcription factor ___, which initiates the cascade of cartilage- and bone-forming genes for vertebral formation

A

PAX1

66
Q

Expression of ___, regulated by __ proteins from the dorsal neural tube, marks
the dermomyotome region of the somite

A

PAX3 - WNT

67
Q

WNT proteins from the dorsal neural tube also target the dorsomedial portion of the somite, causing it to initiate expression of the muscle-specific gene ___ and to form primaxial muscle precursors

A

MYF5

68
Q

The midportion of the dorsal epithelium of the somite is directed by ____, secreted by the dorsal region of the neural tube, to form dermis

A

neurotrophin 3 (NT-3)

69
Q

In cervical and upper thoracic regions, it forms segmental cell clusters (future __), whereas more caudally, it forms an unsegmented mass of tissue, the nephrogenic cord

A

nephrotomes

70
Q

In cervical and upper thoracic regions, it forms segmental cell clusters (future nephrotomes), whereas more caudally, it forms an unsegmented mass of tissue, the ___

A

nephrogenic cord

71
Q

___ splits into parietal (somatic) and Visceral (splanchnic) layers, which line the intraembryonic cavity and surround the organs, respectively

A

Lateral plate mesoderm

71
Q

Lateral plate mesoderm splits into ___ and ___, which line the intraembryonic cavity and surround the organs, respectively

A

parietal (somatic) and Visceral (splanchnic) layers

71
Q

Mesoderm cells of the parietal layer surrounding the intraembryonic cavity form thin membranes, the ____ or ____, which will line the peritoneal, pleural, and pericardial cavities and secrete serous fluid

A

mesothelial membranes, or serous membranes

72
Q

Blood cells and blood vessels also arise from
mesoderm. Blood vessels form in two ways: ____, whereby vessels arise from blood islands, and ____, which entails sprouting from existing vessels

A

vasculogenesis - angiogenesis

73
Q

These islands arise from mesoderm cells that are induced to form ___, a common precursor for vessel and blood cell formation

A

hemangioblasts

73
Q

The definitive ____ are derived from mesoderm surrounding the aorta in a site near the developing mesonephric kidney called the aorta-gonad-mesonephros region (AGM)

A

hematopoietic stem cells

73
Q

The definitive hematopoietic stem cells are derived from mesoderm surrounding the aorta in a site near the developing mesonephric kidney called the ____

A

aorta-gonad-mesonephros region (AGM)

74
Q

___ induces blood island development from competent mesoderm cells that form hemangioblasts

A

FGF2

75
Q

Hemangioblasts are directed to form blood cells and vessels by ____, which is secreted by surrounding mesoderm cells

A

vascular endothelial growth factor (VEGF)

76
Q

The signal to express VEGF may involve HOXBS, which upregulates the VEGF receptor ___

A

FLKl

77
Q

Hemangioblasts in the center of blood islands form ____, the precursors of all blood cells, whereas peripheral hemangioblasts differentiate into angioblasts, the precursors to blood vessels

A

hematopoietic stem cells

78
Q

Hemangioblasts in the center of blood islands form hematopoietic stem cells, the precursors of all blood cells, whereas peripheral hemangioblasts differentiate into ___, the precursors to blood vessels

A

angioblasts

79
Q

Maturation and modeling of the vasculature are regulated by other growth factors, including ____ and ___, until the adult pattern
is established

A

platelet-derived growth factor (PDGF) and TGF-B

80
Q

In turn, VEGF expression induces the ____ (a transmembrane receptor pathway), which specifies arterial development through expression of ____ (ephrins are ligands that bind to Eph receptors in a pathway involving tyrosine kinase signaling)

A

NOTCH pathway - EPHRINBZ

81
Q

In turn, VEGF expression induces the NOTCH pathway (a transmembrane receptor pathway), which specifies arterial development through expression of EPHRINBZ (ephrins are ligands that bind to ____ in a pathway involving ____)

A

Eph receptors - tyrosine kinase signaling

81
Q

_____ are abnormally dense collections of capillary blood vessels that form the most common tumors of infancy, occurring in approximately 10% of all births

A

Capillary hemangiomas

82
Q

NOTCH signaling also upregulates expression of _____, a vein-specific gene, but how this gene and others specify venous development is not clear

A

EPHB4

83
Q

On the other hand, _____, a homeodomain-containing transcription factor, appears to be the master gene for lymphatic vessel differentiation

A

PROXI

84
Q

Failure of the lateral body folds to close the body wall results in ____

A

ventral body wall defects

85
Q

The tube is divided into three regions:
the ____, ___ and ___

A

foregut, midgut, and hindgut

86
Q

The midgut communicates with the yolk sac by way of a broad stalk, the ___

A

Vitelline (yolk sac) duct

87
Q

At its cephalic end, the foregut is temporarily bounded by an ectodermal—endodermal membrane called the ____

A

oropharyngeal membrane

88
Q

This membrane separates the ___, the primitive oral cavity derived from ectoderm, from the pharynx, a part of the foregut derived from endoderm

A

stomodeum

89
Q

The hindgut also terminates temporarily at an ectodermal—endodermal membrane, the _____

A

cloacal membrane

90
Q

This membrane separates the upper part of the anal canal, derived from endoderm, from the lower part, called the ____, which is formed by an invaginating pit lined by ectoderm

A

proctodeum

91
Q

Another important result of cephalocaudal growth and lateral folding is partial incorporation of the allantois into the body of the embryo, where it forms the ___

A

cloaca

92
Q

_____ genes are known for their homeodomain, a DNA-binding motif, the homeobox

A

Homeobox

92
Q

During further development, endoderm gives rise to the following:
- The epithelial lining of the respiratory tract
- The ____ of the thyroid, parathyroids, liver, and pancreas
- The reticular stroma of the tonsils and the thymus
- The epithelial lining of the urinary bladder and the urethra
- The epithelial lining of the tympanic cavity and auditory tube

A

parenchyma

93
Q

Homeobox genes are known for their ___, a DNA-binding motif, the homeobox

A

homeodomain

94
Q

Homeobox genes are known for their homeodomain, a DNA-binding motif, the ___

A

homeobox

95
Q

Many homeobox genes are collected into ____, although other genes also contain the homeodomain

A

homeotic clusters

96
Q

An important cluster of genes specifying the craniocaudal axis is the homeotic gene complex ____ in Drosophila

A

Hom-C

97
Q

These genes are conserved in humans, existing as four copies—___, ____, ____, and ___, — which are arranged and expressed like those in Drosophila

A

HOXA, HOXB, HOXC, and HOXD

97
Q

These genes, which contain the ___ and ___ classes of homeotic genes, are organized on a single chromosome as a functional unit

A

Antennapedia and Bithorax

98
Q

Genes with the same number, but belonging to different clusters, form a ___ group, such as HOXA4, HOXB4, HOXC4, and HOXD4

A

paralogous

99
Q

The pattern of expression of these genes, along with evidence from ____ experiments in which mice are created that lack one or more of these genes, supports the hypothesis that they play a role in cranial-to-caudal patterning of the derivatives of all three germ layers

A

knockout

100
Q

Because counting somites becomes difficult during the second month of development, the age of the embryo is then indicated as the ____ and expressed in millimeters

A

crown-rump length (CRL)

101
Q

The former are located dorsal to the pericardial swelling at the level of the fourth cervical to the first thoracic somites, which explains their innervation by the ____

A

brachial plexus

102
Q

These grooves, known as ___, appear in the hand region first and shortly afterward in the foot, as the upper limb is slightly more advanced in development than the lower limb

A

rays

102
Q

Crown - rump length is 10-14mm in what week?

A

6

102
Q

Crown - rump length is 5-8mm in what week?

A

5

103
Q

Crown - rump length is 17-22mm in what week?

A

7

104
Q

Crown - rump length is 28-30mm in what week?

A

8

105
Q

Most major organs and organ systems are formed during the ____. This period, which is critical for normal development, is therefore called the period of____ or ___

A

third to eighth weeks - organogenesis or embryogenesis

106
Q

The ____ gives rise to the organs and structures that maintain contact with the outside world:
- Central nervous system
- Peripheral nervous system
- Sensory epithelium of ear, nose, and eye
- Skin, including hair and nails
- Pituitary, mammary, and sweat glands and
- enamel of the teeth

A

ectodermal germ layer

107
Q

Characteristic feature: Apperance of primitive streak - what days of embryonic period?

A

14-15

108
Q

Characteristic feature: Notochordal process appears; hemopoietic cells in yolk sac - what days of embryonic period?

A

16-28

109
Q

Characteristic feature: Intraembryonic mesoderm spreads under cranial ectoderm; primitive streak continues; umbilical vessels and cranial neural folds begin to form. - what days of embryonic period?

A

19-20

110
Q

Characteristic feature: Cranial neural folds elevated and deep neural groove established; embryo begins to bend - what days of embryonic period?

A

20-21

111
Q

Characteristic feature: Fusion of neural folds begins in cervical region; cranial and caudal neuropores open widely; visceral arches 1 and 2 present; heart tube begins to fold. - what days of embryonic period?

A

22-23

112
Q

Characteristic feature: Cephalocaudal folding under way; cranial neuropore closing or closed; optic vesicles formed; otic placodes appear - what days of embryonic period?

A

24-25

113
Q

Characteristic feature: Caudal neuropore closing or closed; upper limb buds appear; three pairs of visceral arches - what days of embryonic period?

A

26-27

114
Q

Characteristic feature: Fourth visceral arch formed; hind limb buds appear; otic vesicle and lens placode - what days of embryonic period?

A

28-30

115
Q

Characteristic feature: Forelimbs paddle-shaped; nasal pits formed; embryo tightly C-shaped - what days of embryonic period?

A

31-35

116
Q

Characteristic feature: Digital rays in hand and foot plates; brain vesicles prominent; external auricle forms from auricular hillocks; umbilical herniation initiated - what days of embryonic period?

A

36-42

117
Q

Characteristic feature: Pigmentation of retina visible; digital rays separate; nipples and eyelids formed; maxillary swelling fuse with medial nasal swellings as upper lip forms; prominent umbilical herniation - what days of embryonic period?

A

43-49

118
Q

Characteristic feature: Limmbs long, bent at elbows, knees; fingers, toes free; face more humanlike; tail disappears; umbilical herniation persists to end of third month - what days of embryonic period?

A

50-56

Embryology (21 decks)

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