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EMBRYOLOGY > The Embryonic Period > Flashcards

The Embryonic Period Flashcards

1
Q

Embryonic period

A

Period of organogénesis

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2
Q

The embryonic period occurs from the __ of development.

A

Third to the eighth weeks

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3
Q

It 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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4
Q

It is formed when the 💡notochord and 💡prechordal mesoderm induces the overlying ectoderm to thicken.

A

Neural plate

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5
Q

It is the 💡cells that make up the neural plate.

A

Neuroectoderm

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6
Q

It promotes a neural pathway by an unknown mechanism while it represses 💡BMP transcription and upregulates expression of 💡💡CHORDIN and 💡NOGGIN

A

Fibroblast growth factor (FGF)

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7
Q

They are up regulated by the 💡FGF, which inhibit 💡BMP activity.

They 💡neuralize ectoderm by inhibiting BMP and cause 💡mesoderm to become 💡notochord and 💡paraxial mesoderm (dorsalizes mesoderm).

They induce only 💡forebrain and 💡midbrain types of tissues.

A

CHORDIN and NOGGIN (+ Follistatin)

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8
Q

It 💡permeates the mesoderm and ectoderm of the gastrulating embryo, ectoderm is induced to form epidermis, and mesoderm forms intermediate and lateral plate mesoderm.

A

Bone Morphogenetic Protein 4 (BMP4)

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9
Q

These are secreted proteins that induces 💡caudal neural plate structures (hindbrain and spinal cord)

A

WNT3a and FGF

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10
Q

It play a role in organizing the 💡cranial-to-caudal axis because it can cause 💡respecification of cranial segments into more caudal ones by regulating expression of 💡homeobox genes

A

Retinoic acid (RA)

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11
Q

It is the process whereby the 💡neural plate forms the 💡neural tube.

Formation of 💡neural folds and 💡neural groove.

A

Neurulation

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12
Q

What is the key events in neurulation?

A

Lengthening of the neural plate and body axis

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13
Q

It is a phenomenon whereby there is a 💡lateral to medial movement of cells in the plane of the ectoderm and mesoderm.

The process is regulated by signaling through the 💡planar cell polarity pathway and is essential for 💡neural tube development.

A

Convergent extension

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14
Q

Fusion of neural folds begins in the __ and proceeds cranially and caudally

A

Cervical region (fifth somite)

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15
Q

It is the result of the 💡fusion of neural folds as they approach each other in the midline

A

Neural tube

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16
Q

The cephalic and caudal ends of the neural tube communicate with the amniotic cavity by way of the __ and __.

A

Anterior and posterior neuropores

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17
Q

Closure of the cranial neuropore occurs at approximately at what day?

A

Day 25 (18- to 20-somite stage)

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18
Q

The posterior neuropore closes at what day?

A

day 28 (25-somite stage)

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19
Q

When neurulation is completed, the CNS is represented by __, the spinal cord, and a much broader cephalic portion is characterized by a number of dilations which is called __?

A

Closed tubular structure with a narrow caudal portion

Brain vesicles

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20
Q

As the neural folds elevate and fuse, cells at the lateral border or crest of the neuroectoderm begin to dissociate from their neighbors.

They also form and migrate from cranial neural folds, leaving the neural tube before closure in this region

A

Neural Crest Cells

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21
Q

As neural crest cells leaves the neuroectoderm by active migration and displacement to enter the underlying mesoderm they undergo what kind of transition?

A

Epithelial-to-mesenchymal transition

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22
Q

It refers to 💡cells derived from the 💡epiblast and 💡extraembryonic tissues.

A

Mesoderm

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23
Q

It refers to 💡loosely organized embryonic connective tissue regardless of origin.

A

Mesenchyme

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24
Q

Crest cells from the trunk region leave the neuroectoderm after closure of the neural tube and migrate along one of two pathways:

A

(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
(2) A ventral pathway through the anterior half of each so- mite to become sensory ganglia, sympathetic and enteric neurons, Schwann cells, and cells of the adrenal medulla

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25
Q

Neural crest cells contribute to the:

A

Craniofacial skeleton as well as neurons for cranial ganglia, glial cells, melanocytes

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26
Q

Fourth germ layer

A

Neural Crest Cells

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27
Q

The ectodermal germ layer gives rise to organs and structures that maintain contact with the outside world:

A

■ The central nervous system
■ The peripheral nervous system
■ The sensory epithelium of the ear, nose, and eye
■ The epidermis, including the hair and nails

In addition, it gives rise to the following:
■ The subcutaneous glands
■ The mammary glands
■ The pituitary gland
■ Enamel of the teeth
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28
Q

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

A

Paraxial mesoderm

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29
Q

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

A

Lateral plate.

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30
Q

A layer continuous with mesoderm covering the 💡amnion, known as the?

A

Somatic or parietal mesoderm layer

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31
Q

A layer continuous with mesoderm covering the 💡yolk sac, known as the?

A

Splanchnic or visceral mesoderm layer

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32
Q

Together, these layers (somatic/splanchnic mesoderm layer) 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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33
Q

It 💡connects 💡paraxial and 💡lateral plate mesoderm

A

Intermediate mesoderm

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34
Q

It is a 💡paraxial mesoderm that is 💡organized into segments.

They first appear in the 💡cephalic region of the embryo, and their formation proceeds cephalocaudally.

A

Somitomeres

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35
Q

💡Somitomeres in the 💡head region form in association with segmentation of the 💡neural plate.

A

Neuromeres

36
Q

It is a process where 💡somites [exist as a ball of mesoderm (fibroblast- like) cells] 💡arrange themselves in a donut shape around a small lumen

A

Epithelization

37
Q

💡Part of somite that will become the 💡tendón cartilage and bone component

A

Sclerotome

38
Q

💡Part of somite that provides the segmental 💡muscle component

A

Myotome

39
Q

💡Part of somite which forms the 💡dermis of the back.

A

Dermatome

40
Q

They are produced by the 💡notochord and 💡floor plate of the neural tube, induce the 💡ventromedial portion of the somite to become 💡sclerotome.

A

NOGGIN genes and sonic hedgehog (SHH)

41
Q

It initiates the 💡cascade of cartilage- and bone-forming genes for 💡vertebral formation.

A

PAXl

42
Q

Regulates Expression of 💡PAX3 from the dorsal neural tube, marks the 💡dermomyotome región of the somite.

A

WNT proteins

43
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 to form 💡primaxial muscle precursors.

A

MYF5

44
Q

It is a 💡muscle-specific gene that directs the formation of 💡primaxial and 💡abaxial muscle precursors.

A

MYOD

45
Q

It is secreted by the 💡dorsal region of the neural tube that directs the 💡midportion of the dorsal epithelium to form 💡dermis.

A

Neurotrophin 3 (NT-3)

46
Q

It 💡temporarily connects 💡paraxial mesoderm with the 💡lateral plate differentiates into 💡urogenital structures.

A

Intermediate mesoderm

47
Q

💡Intermediate mesoderm that forms 💡segmental cell clusters in 💡cervical and 💡upper thoracic regions

A

Nephrotomes

48
Q

💡Intermediate mesoderm that forms an 💡unsegmented mass of tissue caudally.

A

Nephrogenic cord

49
Q

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

A

Lateral Plate Mesoderm

50
Q

These are 💡thin membranes formed by mesoderm cells of the parietal layer surrounding the intraembryonic cavity

They will line the 💡peritoneal, 💡pleural, and 💡pericardial cavities and secrete 💡serous fluid

A

Mesothelial membranes, or serous membranes

51
Q

Blood vessels form in two ways:

A

Vasculogenesis

Angiogenesis

52
Q

It a process of blood vessels formation whereby vessels arise from 💡blood island

A

Vasculogenesis

53
Q

It a process of blood vessels formation which entails 💡sprouting from existing vessels

A

Angiogenesis

54
Q

It is a 💡common precursor for 💡vessel and 💡blood cell formation.

A

Hemangioblasts

55
Q

It is a 💡site near the developing 💡mesonephric kidney

A

Aorta-gonad-mesonephros region (AGM)

56
Q

It induces 💡blood island development from competent mesoderm cells that form hemangioblasts.

A

FGF2

57
Q

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

A

Vascular endothelial growth factor (VEGF)

58
Q

It upregulates the 💡VEGF receptor FLKl

A

HOXB5

59
Q

Hemangioblasts in the center of blood islands form the 💡precursors of all blood cells

A

Hematopoietic stem cells

60
Q

It is 💡differentiated peripheral hemangioblasts

The 💡precursors to blood vessels.

A

Angioblasts

61
Q

💡Maturation and 💡modeling of the vasculature are regulated by other growth

A

Platelet-derived growth factor (PDGF) and TGF-beta

62
Q

It is the 💡main organ system derived from the 💡endodermal germ layer.

A

Gastrointestinal tract

63
Q

This germ layer 💡covers the ventral surface of the embryo and forms the 💡roof of the yolk sac

A

ENDODERMAL GERM LAYER

64
Q

The tube is divided into three regions:

A

Foregut, midgut, and hindgut

65
Q

It is a region of the tube which communicates with the yolk sac by way of a 💡broad stalk, the 💡vitelline (yolk sac) duct.

A

Midgut

66
Q

It is a region of the tube where at its 💡cephalic end is 💡temporarily bounded by an 💡ectodermal-endodermal membrane called the 💡oropharyngeal membrane

A

Foregut

67
Q

It separates the 💡stomodeum, the 💡primitive oral cavity derived from ectoderm, from the 💡pharynx, a part of the 💡foregut derived from endoderm.

In the fourth week, it ruptures, establishing an open connection between the 💡oral cavity and the 💡primitive gut

A

Oropharyngeal membrane

68
Q

It is a 💡region of the tube that also 💡terminates temporarily at an 💡ectodermal-endodermal membrane, the 💡cloacal membrane.

A

Hindgut

69
Q

This membrane separates the 💡upper part of the anal canal, derived from endoderm, from the 💡lower part, called the 💡proctodeum,

The membrane 💡breaks down in the seventh week to 💡create the opening for the anus.

A

Cloacal membrane

70
Q

It is formed by an 💡invaginating pit lined by ectoderm.

This membrane breaks down in the seventh week to create the 💡opening for the anus.

A

Proctodeum

71
Q

During further development, endoderm gives rise to the following:

A

■ The epithelial lining of the respiratory tract
■ The parenchyma of the thyroid, parathyroid, 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

72
Q

These genes are known for their 💡homeodomain.

They code for transcription factors that activate cascades of genes regulating phenomena such as segmentation and axis formation.

A

Homeobox genes

73
Q

It is a 💡DNA-binding motif, the homeobox.

A

Homeodomain

74
Q

It 💡collects homeobox genes

A

Homeotic clusters

75
Q

It is a 💡homeotic gene complex from Drosophila which is important cluster of genes specifying the 💡craniocaudal axis.

A

Hom-C

76
Q

It indicates the 💡age of the embryo because counting somites becomes difficult during the second month of development and expressed in millimeters.

It is the measurement from the 💡vertex of the skull to the midpoint be- tween the apices of the 💡buttocks.

A

Crown-rump length (CRL)

77
Q

Radial grooves

They 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

78
Q

It result when neural tube closure fails to occur.

A

Neural tube defects (NTDs)

79
Q

If the neural tube fails to dose in the cranial región, then most of the brain fails to form, and the defect is called?

A

Anencephaly

80
Q

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

A

Spina bifida

81
Q

The most common site for spina bifida to occur is in the?

A

Lumbosacral region

82
Q

These 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

83
Q

It is highly expressed in the lesions and may be one factor promoting abnormal vessel growth.

A

INSULIN-LIKE GROWTH FACTOR 2

84
Q

Most major organs and organ systems are formed during the __.

the time when most gross structuralbirth defects are induced.

A

Third to eighth weeks

85
Q 
Crown-Rump Length (mm):
5-8
10-14
17-22
28-30
A 
Approximate Age (wk):
5
6
7
8

EMBRYOLOGY (7 decks)

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