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Human Development (BSC5314) > Week 3 Development > Flashcards

Week 3 Development Flashcards

0
Q

Is pregnancy detectable in the 3rd week?

A

yes, by ultrasound

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1
Q

What does the 3rd week of development coincide with?

A
  • coincides with 1st week after missed menstrual period
  • embryo is already 2 weeks old
  • 5 weeks after last normal menstrual period (LNMP)
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2
Q

Where is the epiblast?

A

adjacent to amniotic cavity

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3
Q

where is the hypoblast?

A

adjacent to umbilical vesicle

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4
Q

Where is the prechordal plate?

A

thickened circular area of columnar hypoblast cells

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5
Q

The prechordal plate will eventually form what?

A
  • organizes development of the head region

- future site of the mouth

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6
Q

What is the outcome of gastrulation?

A

establishes axial orientation in embryo

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7
Q

What does morphogenesis mean?

A

development of the body form begins now

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8
Q

Where does the primitive streak appear?

A

thickened median linear band on the dorsal and caudal surface of the epiblast (first sign of gastrulation)

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9
Q

What is causing the primitive streak to form?

A

forms as epiblast cells proliferate and migrate to the median plane

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10
Q

What orientation landmarks are established in the primitive streak?

A

primitive node, primitive pit, primitive groove

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11
Q

Where is the primitive node?

A

Accumulated epiblast cells at the cranial end of the primitive streak

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12
Q

Where is the primitive pit?

A

small depression in the primitive node

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13
Q

Where is the primitive groove?

A
  • narrow depression oriented lengthwise within the primitive streak
  • the pit and groove form as epiblast cells migrate inward through the primitive streak
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14
Q

How is embryonic endoderm formed?

A

as a result of epiblasts migrating inward through the primitive streak some epiblast cells displace the original hypoblast cells

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15
Q

What is the embryonic mesoderm?

A

as a result of epiblasts migrating inward through the primitive streak some epiblast cells take up position between the epiblast and the original hypoblast
- become mesoblasts which will form the embryonic mesoderm

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16
Q

What is mesenchyme?

A

a rudimentary connective tissue

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17
Q

Where does mesenchyme migrate?

A

migrate laterally to reach extraembryonic mesoderm of umbilical vesicle & amnion

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18
Q

How does mesenchyme relate to extraembryonic mesoderm?

A

as a result of epiblasts migrating inward through the primitive streak some epiblast cells from embryonic mesoderm and others form mesenchym

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19
Q

Where is the cardiogenic area?

- What will develop here?

A

mesenchyme will migrate cranially on either side of the prechordal plate into cardiogenic area
- site where the heart begins developing

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20
Q

What cell types develop from mesenchyme?

A

highly migratory cells which become fibroblasts, chondroblasts, osteobasts
- mesenchyme can also form ectoderm and endoderm

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21
Q

What is embryonic ectoderm?

A

the remaining epiblast cells which migrated inward through the primitive streak become the embryonic ectoderm

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22
Q

When does mesoderm production diminish?

A

early week 4

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23
Q

When does the primitive streak degenerate?

A

disappears by end of week 4

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24
Q

When is gastrulation completed?

A

end of 4th week

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25
Q

What are the results of gastrulation?

A

embryo having 3 layers:

  • ectoderm
  • mesoderm
  • endoderm
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26
Q

What does the ectoderm give rise to?

A
  • epidermis and appendages
  • nervous system and pituitary gland
  • sensory epithelia of the eye, ear and nose
  • connective tissues of the head (via neural crest cells)
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27
Q

What does endoderm give rise to?

A
  • epithelial linings of respiratory and GI tracts
  • epithelial lining of the urinary bladder and urethra
  • glandular cells of the liver, pancreas and salivary glands
  • tonsils, thymus, thyroid and parathyroid glands
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28
Q

What does mesoderm give rise to?

A
  • striated muscle
  • smooth muscle
  • heart
  • blood vessels
  • blood cells
  • ducts and organs in the urinary and reproductive systems
  • connective tissues in the body and extremities (including bone and cartilage)
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29
Q

Is a sacrococcygeal teratoma benign or mallignant?

- common?

A

usually benign that develops from remnants of primitive streak
- most common tumor in newborns (1/35000; 80% female)

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30
Q

What is the notochord process?

A

median cellular cord of mesenchymal cells migrating cranially from primitive node

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31
Q

Where is the notochord located?

A

lengthens in the mesodermal plane until it reaches the prechordal plate

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32
Q

What is the prechordal plate?

A

columnar endodermal cells in contact with the overlying ectoderm
- no intervening mesoderm located here

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33
Q

What is the oropharyngeal membrane?

A

future site of mouth

- prechordal plate is a precursor

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34
Q

What is the cloacal membrane?

- whats unique about its construction?

A

circular area caudal to the primitive streak (future site of anus)
- endoderm and ectoderm in contact here

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35
Q

By middle of week 3, embryonic mesoderm separates endoderm from ectoderm everywhere except where?

A
  • oropharyngeal membrane (cranially)
  • cloacal membrane (caudally)
  • along the notochord process (which is mesenchyme)
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36
Q

What does the notochordal process become?

A

a rod-lie structure called the notochord

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37
Q

What are the functions of the notochord?

A
  • defines the longitudinal axis of the embryo
  • provides some rigidity to the embryo
  • provides signals necessary for development of the CNS
  • provides signals necessary for development of axial musculoskeletal structures
  • contributes to development of intervertebral discs
    • adult derivative persists s nucleus pulposus of IVD
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38
Q

What is the process of neurolation?

A

neural tube formation

39
Q

When does neurolation occur?

A

begins in week 3, completed by end of week 4

40
Q

What is a neurula?

A

name for the embryo during this time period

41
Q

What is the neural plate?

A

thickened midline ectodermal cells (neuroectoderm)

42
Q

How does the neural plate form?

A

form as a response to underlying notochord induction

43
Q

Where is the neural plate located?

A

eventually extends cranially, beyond the end of the notochord

44
Q

What does the neural plate give rise to?

A

responsible fro giving rise to brain and spinal cord (CNS)

45
Q

What are the neural groove and neural folds?

A
  • most prominent cranially where the brain will develop

- develop from neural plate on approximately day 18

46
Q

How does the neural tube form?

A

forms by closure of the neural folds

47
Q

Where does the neural tube close initially?

- separates from ectoderm

A
  • closure begins in cervical region and progresses from there cranially and caudally
  • separates from and is covered by surface exctoderm
48
Q

Where is the cranial neuropore?

-where does it close?

A
  • cranial opening in neural tube

- closes on approximately day 25

49
Q

Where is the caudal neuropore?

- when does it close?

A
  • caudal opening in neural tube

- closes on approximately day 27

50
Q

Where do neural crest cells originate?

A

migratory cells originating from the “crest” of the neural folds

51
Q

Where do neural crest cells migrate?

A

initially migrate to the dorsolateral region adjacent to the neural tube
- in this position they give rise to sensory ganglia for spinal and cranial nerves

52
Q

What do neural crest cells give rise to?

A
  • sensory neurons
  • Postganglionic autonomic neurons
  • Schwann cells
  • Melanocytes
  • Suprarenal medulla cells
  • CT in head
53
Q

What is the basis for neural tube defects

A

disturbances to development in week 3 may result in severe abnormalities in the brain and spinal cord

54
Q

Why do neural tube defects occur?

A

due to failure of the neural tube to fuse and close into a neural tube

- often attributed to a teratogenic drug
- may also be linked to problems arising during embryo folding
55
Q

What is meroencephaly?

A

partially absence of brain (most common and very severe defect)

56
Q

What is anencephaly?

A

complete absence of brain (misnomer)

57
Q

Where is paraxial mesoderm?

A

located immediately adjacent to notochord

58
Q

How was paraxial mesoderm formed?

A

derived from mesoderm cells migrating through lateral part of primitive node and cranial part of primitive streak

59
Q

What structures will paraxial mesoderm form?

A

will form somites

60
Q

Where do somites first form?

A
  • paired cuboidal structures formed from paraxial mesoderm

- form in craniocaudal sequence on either side of notochord and neural tube

61
Q

Where do somites first appear?

A

first appear in future occipital region of embryo (late in week 3)

62
Q

how many somites pairs form?

A

42-44 pairs will be present by end of week 5

63
Q

At what rate do somites develop?

A

somites develop at a rate approximately 3 pair/day

64
Q

Whats a criteria used in aging embryos?

A

number of somites present

65
Q

What is a segmentation clock?

A

regulated pattern of somite development depends on cyclic gene expression

66
Q

What somites are formed?

A
  • 4 occipital (first on disappears)
  • 8 cervical
  • 12 thoracic
  • 5 lumbar
  • 5 sacral
  • 8-10 coccygeal (last 5-7 disappear)
67
Q

What do somites give rise to?

A
  • give rise to most axial and appendicular musculature and axial skeleton
  • give rise to adjacent dermis of skin
68
Q

Where is the intermediate mesoderm located?

A

mid region of primitive streak

69
Q

What is the intermediate mesoderm derived from?

A

derived from mesoderm cells migrating through mid region of primitive streak

70
Q

What will intermediate mesoderm form?

A

will form urogenital structures

71
Q

Where is the lateral plate mesoderm located?

A

continuous with extraembryonic mesoderm (located within chorion)

72
Q

Where is the lateral plate mesoderm derived from?

A

derived from mesoderm cells migrating through caudal part of primitive streak

73
Q

What will the lateral plate mesoderm form?

A

forms the body wall structures

74
Q

Where does the Intraembryonic coelom for initially?

A

forms initially as spaces develop within the lateral plate mesoderm

75
Q

What is continuous with the Intraembryonic coelom

A

As the spaces coalesce they form the intraembryonic coelom

- initially continuous with extraembryonic coelom (chorionic cavity)

76
Q

What will the Intraembryonic coelom eventually become?

A

divides the lateral plate mesoderm into 2 layers:

  • somatic or parietal layer
  • splanchnic or visceral layer
77
Q

Where is the somatic or parietal layer?

A

located adjacent to the ectoderm and continuous with the extraembryonic somatic mesoderm covering the amnion

78
Q

What is somatopleure?

A

comprised of parietal lateral plate mesoderm and overlying ectoderm

79
Q

What will somatopleure form?

A

embryonic body wall

80
Q

Where is the splanchnic or visceral layer?

A

located adjacent to the endoderm and continuous with the extraembryonic splanchnic mesoderm surrounding the umbilical vesicle

81
Q

What is the splanchnopleure?

A

comprised of visceral lateral plate mesoderm and underlying endoderm

82
Q

What will splanchnopleure form?

A

embryonic gut

83
Q

Through week 2, embryo nutrition is sustained via what?

A

diffusion

84
Q

In week 3 in early cardiovascular system development, what begins forming?

A

blood vessels

85
Q

What is vasculogenesis?

A

formation of new blood vessels by precursor cells in mesoderm

86
Q

What is angiogenesis?

A

formation of new blood vessels by budding/branching of preexisting vessels

87
Q

What are angioblasts?

A

mesenchymal cells that form blood vessels

88
Q

Where do angioblasts cluster?

A

they cluster to form blood islands in the extraembryonic splanchnic mesoderm
- small cavities appear within these blood islands

89
Q

How do endothelial cells form?

A

angioblasts near the cavities within blood islands flatten to form endothelial cells

90
Q

How do erythrocytes form?

A

blood cells develop from endothelial cells in vessels adjacent to the umbilical vesicle
- embryonic hematopoiesis begins later (in week 5)

91
Q

Where is the cardiogenic area?

A

mesenchyme around and cranial to the oropharyngeal membrane

92
Q

How is a primordial heart tube formed?

A

paired longitudinal endocardial tubes fuse

93
Q

What do the heart tube join with?

A

blood vessels in embryo, connecting stalk, chorion and umbilical vesicle to form a rudimentary cardiovascular system

94
Q

When does the hear begin beating?

A

by the end of week 3

95
Q

Which organ system is the first to start functioning?

A

cardiovascular system

Human Development (BSC5314) (34 decks)

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