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anatomy 1-9 > L5: embryonic & fetal periods > Flashcards

L5: embryonic & fetal periods Flashcards

1
Q

How long is the embryonic period?

A

Weeks 3 – 8 (embryonic period)

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2
Q

When should the Organogenesis be completed

A

Weeks 3 – 8 (embryonic period)

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3
Q

What does The Mesoderm differentiates to ?

A

Paraxial,
Intermediate,
Lateral

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4
Q

What is Extraembryonic cavity that form In the 2nd week?

A

1- YolkSac

2- Chorionic Cavity

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5
Q

What does Extraembryonic splits into?

A
  1. Splanchnic layer

2. Somatic layer

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6
Q

What is the role of the notochord?

A

1- Form body axes
2- Expresses a lot of genes
3- Regulates mesoderm dorsalizing

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7
Q

What will the The lateral Mesoderm split into?

A

1- One within the endoderm (splanchnic or visceral,will be in association with the developing gut)

2- one within the amniotic cavity (somatic)

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8
Q

What does Gastrulation establishe?

A

establishes the three germ layers, namely

Ectoderm,
endoderm,
mesoderm.

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9
Q

What is the importance of the germ layers?

A

form different tissues and organs (organogenesis)

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10
Q

what do we have at the End of the embryonic period?

A

1- Main organ systems are formed

2- External body form is recognizable Notochord induces (an inducer) the ectoderm to form the neural plate

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11
Q

What does the notochord do once it’s formed?

A

begins to signal to the ectoderm above it to differentiate these cells especially in the cephalic region to change into neuroectoderm (to fold)

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12
Q

What makes the neuroectoderm?

A

Cells of the neural plate make up the neuroectoderm

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13
Q

What happens to the neural plate during neurulation?

A

Begins to expand toward the primitive streak

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14
Q

What is the role of the primitive node during neurulation?

A

Organizer expresses specific genes to from the notochord

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15
Q

Where does the neural plate expands to ?

A

Toward the primitive streak

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16
Q

What are the Somites?

A

part of the mesoderm

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17
Q

when does somites start to appear?

A

During neurulation day 20

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18
Q

Somites will differentiate to form?

A

1- Sclerotome > bones&vertebra

2- Myotome > muscles

3- Dermatome > skin

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19
Q

When is the neural folds formed?

A

By the end of the 3rd week

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20
Q

What forms the neural plate

A

• the lateral edges of the neural plate

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21
Q

What forms the the neural groove?

A

The depressed mid-region

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22
Q

How is the neural groove formed

A

• Gradually the neural folds approach each other in the midline, where they fuse

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23
Q

Where does Fusion begins?

A

at cervical region (5th somite) and proceeds cranially and caudally, forming the neural tube

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24
Q

Simile acts a landmark for what

A

to tell us which stage of development we are

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25
Q

How does The neural tube close?

A

The neural tube begins to close like a zipper cephalocaudally

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26
Q

How do the cephalic and caudal ends of the neural tube communicate?

A

until fusion is complete > with the amniotic cavity with the anterior (cranial) and posterior (caudal) neuropores, respectively

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27
Q

when does the Closure of anterior neuropore occur?

A

Closure of anterior neuropore occurs about day 25

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28
Q

when does the Closure of posterior neuropore occur?

A

day28

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29
Q

What happens if anterior pore fails to close

A

Anencephaly

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30
Q

What happens If Posterior pore fails to close

A

spina bifida.

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31
Q

What are the differences that occur between the 25 and 28 day?

A

1- Increase in size

2- Umbilical cord formation

3- Closure-of neuropores

4- Otic placode give rise to eyes and ears

5- Limb ridges appear

6- Increase in somite number

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32
Q

What is the role of Broader cephalic portion of the neural tube?( 25 and 28 day)

A

forms the brain

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33
Q

What is the role of narrow caudal portion of the neural tube?( 25 and 28 day)

A

• the narrow caudal portion forms the spinal cord

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34
Q

What are the Derivatives of the ectodermal germ layer ?

A

1- The central nervous system

2- the peripheral nervous system

3- The sensory epithelium of the ear,nose and eye

4- The epidermis and its appendages

5- Subcutaneous glands

6- The mammary glands

7- The pituitary gland

8- Enamel of the teeth

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35
Q

When Formation and migration of Neural crest cells occur?

A

• This is happening during neural tube closure

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36
Q

How does the formation of neural crest cell happen

A
  1. At the dorsal part ,cells begin to detach and migrate from neural tube and as they detach, they change their profile from epithelial to mesenchymal
  2. they will give rise to structures that are associated to the CNS
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37
Q

What are dorsal root ganglion

A

A sensory gateway/door that collects info and it send to the brain

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38
Q

Who forms dorsal root ganglion

A

Neural crest cells

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39
Q

What are sympathetic ganglion

A

Autonomic part and is derived from neural crest cells developing suprarenal ganglion

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40
Q

preaortic ganglion

A

Control vasodilation and vasoconstriction

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41
Q

Interact ganglion

A

Going to GI tract, excelling GI tract to inc or dec digestion

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42
Q

What are the Neural crests formed from?

A

• edges of neural folds

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43
Q

What genes are important for neural crest formation?

A

• BMPs and FGFs

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44
Q

What secretes BMPs and FGFs?

A

secreted from ectoderm

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45
Q

BMPs and FGFs regulate the whole process, why?

A

Because they play role in ventralizing the mesoderm

so this is part of the mesoderm cells as well at this point in time, they are derived from the developing neural tube, they have the ability to shift their profile to become neural crest cell and go to that mesoderm layer and innervate the structure that they are going develop to

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46
Q

Why is Neural crest cells (neuroectodermal) transform from epithelial to mesenchymal form?

A

So they can migrate.

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47
Q

Where do neural crest cells migrate to

A

These cells migrate and enter the mesoderm

48
Q

How do neural crest cells able to migrate

A

An Interaction with ectoderm is required

49
Q

What are the Neural crest derivatives?

A

1- Connective tissue and bones of the skull

2- Cranial and spinal nerve ganglia

3- Septum of the heart

4- Sympathetic chain and sympathetic and parasympathetic ganglia

5- Schwann cells

6- Adrenal medulla

7- Glial cells

8- Melanocytes-in skin and other organs > pigment in skin and daughter organs

9- Odontoblasts-Teeth

50
Q

What are the possible Neural tube defects?

A
  1. Anencephaly

2. B & C- Spina bifida

51
Q

What causes Neural tube defects?

A

• Neural tube fails to close

52
Q

Where does failure to close the Neural tube Occur in anencephaly?

A

• If it happens at the cranial region, then most of the brain fails

53
Q

spina bifida?

A
  • Below the cervical region failed closure results in spina bifida
  • Spina bifida cases commonly occur in the lumbosacral region
54
Q

How can can we prevent Neural tube defects?

A

• Folic acid

55
Q

What does the mesodermal germ layer start to form?

A

• initially the mesodermal germ layer form a thin sheet of loosely woven tissue on each side of the midline

56
Q

what induces the mesoderm to divide into 3 parts?

A

Notochord

57
Q

When does cells close to the midline?

A

On 17th day, cells close to the midline

58
Q

what is the lateral plate?

A

• On 19th day, more laterally the mesoderm layer remains thin and is known as lateral plate

59
Q

What does the Intermediate mesoderm connect?

A

connects paraxial and lateral plate mesoderm

60
Q

What divide the lateral plate into two layers?

A

• Cavities develop in the lateral plate

61
Q

What are the divide layers of the lateral plate?

A

• it is divided into two layers: somatic (parietal)&splanchnic (visceral)layers

62
Q

What are the derivatives of the Somatic mesoderm?

A

• Somatic mesoderm forms dermis of the skin in the body wall & limbs and bones and connective tissue

63
Q

What are the derivatives of the Splanchnic mesoderm?

A

Splanchnic mesoderm forms the muscles of the gut

64
Q

What are the derivatives of the Intermediate mesoderm?

A

Intermediate mesoderm contributes to the formation of the urinary and reproductive
Systems (gonads) > Except bladder and urethra

65
Q

Blood cells and blood vessels arise from

A

mesoderm

66
Q

What is somitomeres?

A

paraxial mesoderm begins to be organized as segments

67
Q

when does start to appear somitomeres?

A

beginning of the 3rd week

68
Q

where do somitomeres first appear?

A

first appear in the cephalic region and their formation proceeds cephalocaudally

69
Q

what do we mean with somites?

A

When Somitomeres further organize they form somites

70
Q

How many somites develop By the end of 5th?

A

By the end of 5th week 42-44 somites develop

71
Q

What is the location of somites?

A
  • occipital,
  • 8 cervical,
  • 12 thoracic,
  • 5 lumbar,
  • 5 sacral
  • 8-10 coccygeal pairs
72
Q

What is the fate of the 1st occipital and last 5-7 coccygeal somites?

A

The 1st occipital and last 5-7 coccygeal somites later disappear

73
Q

Most ventral somite is known as

A

Sclerotome

74
Q

Dorsal medial & ventral lateral are known as

A

Myotome

75
Q

Middorsal

A

dermatome

76
Q

Where are mesoderm cells arranged?

A

around the center of each somite

77
Q

What are the derivates of somites?

A
  • The somites form the axial skeleton (vertebrae, skull, sternum, ribs)
  • body wall muscles
  • dermis of the skin
78
Q

What is the Transcription factor required for the ventral lateral part of the somite? > muscle cells

A

MYOD

79
Q

What regulates MYOD expression?

A
  • WNT from the ectoderm

* lateral plate mesoderm will secrete BMP4 to express MYOD as well

80
Q

What is the Transcription factor required for the middorsal part of the somite? > dermis

and What regulates that expression?

A

PAX3

  • NT- 3
81
Q

Where does NT- 3 come from?

A

coming from dorsal side of N.T

82
Q

What is the Transcription factor required for the dorsal medial part? > muscle cells

A

MYF

83
Q

What regulates MYF expression?

A

WNT coming from the dorsal side of N.T in addition to SHH from notochord and ventral
part of N.t

84
Q

What transcription factor is required in order differentiate somite’s into sclerotome?

A

PAX1

85
Q

What induces PAX1 expression?

A

SHH and Noggin

86
Q

Where is the SHH and Noggin coming from?

A

Ventral part of the neural tube and notochord

87
Q

Describe the visceral mesoderm layer ?

A

This layer is attached to the endoderm and incorporated within the developing fetus

88
Q

What does the endoderm germ layer covers?

A

the ventral surface of the embryo > forms the roof of the yolk sac

89
Q

what happens Between the 17th and 28th days?

A

growth of the brain vesicles and lengthening of the neural tube

90
Q

growth of the brain vesicles and lengthening of the neural tube leads to what

A

causes both the head and tail regions to move ventrally forming cranial and caudal body
folds and the embryo curves into the fetal position > the embryo lies within the amniotic
cavity

91
Q

why does the umbilical region the ventral body wall does not close completely

A

to leave a connection between the yolk sac and the gut

92
Q

What are the Derivatives of the endodermal germ layer?

A
  • the epithelium of primitive gut and the respiratory tract
  • thyroid, parathyroid, liver, pancreas, tonsils and thymus
  • urinary bladder and urethra , tympanic cavity and auditory tube.
93
Q

When does the membrane breaks?

A

During the 4th week

94
Q

How is the the foregut separated from the stomodeum?

A

At the cranial end the foregut is separated from the stomodeum (primitive mouth) by the
oropharyngeal membrane

95
Q

How is the hindgut separated from exterior?

A

At the caudal end, the cloacal membrane separates the hindgut from exterior

96
Q

When does the the cloacal membrane breaks?

A

breaks during 7th week à these two events establish continuity with exterior (amniotic
cavity)

97
Q

Gonads develop from

A

the intermediate mesoderm

98
Q

Bladder and

urethra develop from

A

endoderm

99
Q

Why do external appearance changes occur?

A

due to increase in head size and formation of the limbs, face, ears, nose and eyes (End of 8th week)

100
Q

When does the limbs appear?

A
  • 5th week- limbs appear

* first the upper limbs and then the lower limbs

101
Q

what happens in 2nd month?

A

increase in head size, face, limbs, ears, nose and eyes

102
Q

When are Most organs and organ systems formed?

A

during the embryonic period

103
Q

Why is the embryonic period considered as critical period for development?

A

Because Most organs and organ systems formed

104
Q

Embryonic period ends in

A

8th week > (2-8)

105
Q

When does the Fetal period begin?

A

From 9th week to birth

106
Q

What is the main characteristic of the Fetal period?

A

All systems are in place and completed development but now are maturing and increasing in size

107
Q

what happens to the head during the fetal period

A

Slowdown of head growth compared to rest of the body 3rd Month

108
Q

Second half of intra-uterine life

A

4th and 5th months

109
Q

Why is the skin of the fetus is reddish?

A

Due to high level of angiogenesis (high vascularity)

110
Q

Why are babies that are Born at 6 month-may not survive?

A

The lung development is not complete and alveolar collapse will happen

111
Q

Time of birth

A

266 days/38 weeks after fertilization

112
Q

Doctor calculates the date of delivery as

A

280 days/40 weeks after last period

113
Q

what can misguide the doctor

A

Implantation bleeding

Irregular menstrual period

114
Q

The size of the fetus has to be determined to

A

manage delivery and growth of fetus

115
Q

is intra-embryonic mesoderm inside the baby?

A

Yes Intra-embryonic mesoderm will give rise to Paraxial Intermediate Lateral

116
Q

When lateral splits it will give rise to

A

lining of the gut and membranes around body wall

anatomy 1-9 (9 decks)

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