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ESA1 - Tissues Of The Body > Early Embryonic Development 2 > Flashcards

Early Embryonic Development 2 Flashcards

1
Q

When does the process of gastrulation occur?

A

Week 3

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2
Q

Define ‘gastrulation’

A

Establishment of the 3 germ layers forming the trilaminar disc, whereby all the tissues of the body originate

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3
Q

What defines the start of gastrulation?

A

Formation of the PRIMITIVE STREAK

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4
Q

Where does the primitive streak appear?

A

Dorsal surface at the caudal end of the epiblast

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5
Q

Where is the primitive node located?

A

Cranial end of the primitive streak

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6
Q

Where is the primitive pit located?

A

Centre of the primitive node, which is at the cranial end of the primitive streak

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7
Q

Which direction does the primitive streak develop in?

A

CRANIAL TO CAUDAL

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8
Q

Describe the formation of the trilaminar disc

A
  • Cells of the epiblast layer MIGRATE and INVAGINATE at the primitive streak
  • Forms a cell layer within the bilaminar disc, DISPLACING THE HYPOBLAST and forming 3 germ layers
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9
Q

Describe the migration of the cells forming the mesoderm

A
  • Cells invaginate from epiblast layer and migrate through the primitive streak
  • Cells spread LATERALLY and CEPHALAD towards the head
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10
Q

Why does the mesoderm contain 2 gaps within the cell layer?

A
  • 2 gaps; one cranial and one causal

- Will go on to form the future MOUTH (cranial) and ANUS (caudal)

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11
Q

What is the role of the notochord?

A
  • Forms the basis of the axial skeleton (defines the MIDLINE)
  • Drives the formation of the nervous system by the process of NEURALATION
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12
Q

Describe the formation of the notochord

A
  • PRENOTOCHORDAL CELLS of the epiblast migrate through cranial part of primitive PIT
  • Form a SOLID ROD OF CELLS running down the MIDLINE with an important signalling role
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13
Q

Describe the axes that are set during weeks 3-8

A
  • CRANIAL and CAUDAL (head to tail)
  • DORSAL and VENTRAL (back and belly)
  • LEFT and RIGHT
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14
Q

How is the setting of the axes controlled?

A

Molecular signals from the primitive node ensure correct dorsal/ventral and left/right development

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15
Q

What phenomenon marks the start of the embryonic period?

A

GASTRULATION

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16
Q

What does the trilaminar disc consist of?

A
  • ECTODERM
  • MESODERM
  • ENDODERM
17
Q

How does the primitive node direct certain cells to the left and right sides?

A
  • CILIATED CELLS OF THE PRIMITIVE NODE waft cells in the LEFT HAND direction
  • SIDE SPECIFIC SIGNALLING CASCADES are initiated
  • When the cilia stop moving, the cells move to the RIGHT
18
Q

What is situs inversus?

A
  • COMPLETE MIRROR IMAGE VISCERA

- Results from immotile cilia so correct left/right positions cannot be defined

19
Q

What is the difference between monozygotic and dizygotic twins?

A

MONOZYGOTIC twins are formed from a single fertilised oocyte whereas DIZYGOTIC twins are formed from two separate fertilised ooctyes

20
Q

Describe two methods by which monozygotic twins are formed

A
  • Splitting of embryo after first cleavage and each embryo forms its own placenta (NON IDENTICAL)
  • Duplication of inner cell mass whereby two embryos share the same placenta (IDENTICAL)
21
Q

Describe how conjoined twins are formed

A
  • SPLITTING OCCURS LATE with duplication of the primitive streak
  • Both embryos form in the same amniotic cavity and share the same placenta
  • Sometimes SEPARATION IS NOT COMPLETE
22
Q

What is ‘teratogenesis’?

A

The process through which normal embryonic development is interrupted (most sensitive during weeks 3-8)

23
Q

Why is the pre-embryonic period not susceptible to teratogenesis?

A

Any interruption during implantation of the embryo would result in a MISCARRIAGE

24
Q

Describe when congenital defects may occur during development

A

Teratogenesis VARIES as each organ has a specific window during the development of the embryo in which its development may be affected

25
Q

Give 3 examples of possible teratogenic agents that may cause developmental defects in the embryo

A
  • THALIDOMIDE
  • Alcohol/specific therapeutic drugs
  • Rubella
26
Q

When does the embryonic period occur?

A

Weeks 3-8

ESA1 - Tissues Of The Body (19 decks)

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