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ESA1 > ToB Embryology 2 - Gastrulation > Flashcards

ToB Embryology 2 - Gastrulation Flashcards

1
Q

Which embryonic period is the most perilous for the developing child?

A

Embryonic (weeks 3-8)

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2
Q

What is week 3 known as, and why?

A

‘Week of threes’

  • Three cavities have formed (amniotic, chorionic and yolk sac)
  • Three germ layers produced (Ectoderm, mesoderm and endoderm)
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3
Q

Define gastrulation (in human embryos):

A

The process by which the bilaminar disc (epiblast and hypoblast layers) is converted into the trilaminar disc (ectoderm, mesoderm and endoderm)

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4
Q

What marks the start of gastrulation?

A

The appearance of the primitive streak

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5
Q

What drives and coordinates gastrulation?

A

The primitive streak

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6
Q

How does the appearance of the surface of the epiblast layer differ from the end of the second week to the end of the third week?

A

At the end of the second week it is a uniform disk, but by the end of the third week there is a primitive streak which forms on the dorsal surface.

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7
Q

Describe the appearance of the primitive streak:

A
  • Narrow groove
  • Bulging edges
  • Forms node at the cranial end of the streak
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8
Q

Where is the primitive pit located?

A

It forms at the center of the primitive node, located at the cranial end of the primitive streak

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9
Q

How can you tell the cranial end from the caudal end of the embryo during gastrulation?

A

The primitive node first appears at the caudal end of the embryo, and grows towards the cranial end, forming the primitive node at its cranial end.

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10
Q

During what process can you first tell the cranial end from the caudal end of the embryo?

A

Gastrulation

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11
Q

What type of cells form the trilaminar disc?

A

Epiblast cells

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12
Q

How do the epiblast cells form the 3 layers?

A

The epiblast cells begin to migrate and differentiate, gathering around the primitive streak.
They then push through the epiblast layer, creating a new layer between the epiblast layer and the hypoblast layer, the endoderm.
After that more cells migrate out of the epiblast layer, to form the mesoderm.

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13
Q

Which layer does the hypoblast layer become in the trilaminar disc?

A

The hypoblast layer does not contribute any cells to the trilaminar disc.

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14
Q

Name the 3 layers of the trilaminar disc:

A

1) Ectoderm
2) Mesoderm
3) Endoderm

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15
Q

Why isn’t the trilaminar disc consistent across the cell?

A

There is no mesoderm at 2 places in the trilaminar disc, producing avascular tissue which will form openings at the mouth and anus

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16
Q

What structure is the basis of the axial skeleton, and drives the formation of the nervous system?

A

Notochord

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17
Q

What is the basic 2 functions of the notochord?

A

1) Basis for axial skeleton

2) Drives the formation of the nervous system

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18
Q

What is the origin of the cells which form the notochord?

A

Epiblast cells

19
Q

How do some epiblast cells form the notochord?

A

Prenotochordal cells migrate through the cranial part of the primitive pit, and form a solid rod of cells

20
Q

Describe the appearance of the notochord in the trilaminar disc:

A

A solid rod of cells forming the midline of the disc, in the middle of the mesoderm layer

21
Q

What does the notochord become in a adult human?

A

The inner core of the vertebral discs - ‘nucleus pulposus’

22
Q

What are the 6 main directional anatomical terms (of adult)?

A

1) Superior/cranial
2) Inferior/caudal
3) Anterior/ventral
4) Posterior/dorsal
5) Right
6) Left

23
Q

What sets the axes of the adult human?

A

The notochord in the developing embryo

24
Q

What is the difference in the meaning of ‘anterior’ when describing an embryo vs an adult?

A

Anterior in the embryo refers to the ‘head end’, or rostral,

Anterior in the adult refers to the front, or belly

25
Q

Name the 2 main structures which are formed from the ectoderm:

A

1) Epidermis

2) Nervous system

26
Q

Name 2 types of tissues which derive from the mesoderm:

A

1) Muscular tissue

2) Connective tissue - bone/cartilage/blood/lymph/adipose

27
Q

What is the main role of cells which derive from the endoderm?

A

Epithelial cells which line:

  • GI tract
  • respiratory system
  • urinary system
  • many glands
28
Q

Which layer of the trilaminar disc gives rise to the largest variety of tissues?

A

Mesoderm layer

29
Q

How does the primitive node denote left-right asymmetry of the embryo?

A

Ciliated cells at the primitive node beat in such a way, to send signalling molecules to the left or right, promoting differentiation in a particular area of the developing embryo.

30
Q

What usually causes complete mirror-image of the viscera (situs inversus)? (ie internal organs mirror image to usual placement)

A

Immotile cilia at the primitive node.

31
Q

Why does the gastrulation process complete faster at the cranial end compared to the caudal end of the developing embryo?

A

Because development proceeds ‘cephalocaudally’ (from cranial end to caudal end)

32
Q

What does the term ‘monozygotic twins’ mean?

A

A single fertilised oocyte has given rise to two infants

33
Q

What does the term ‘dizygotic twins’ mean?

A

Two fertilised oocytes produce two infants, during the same pregnancy

34
Q

What type of twins are identical?

A

Monozygotic

35
Q

What are the 2 types of twins?

A

1) Monozygotic

2) Dizygotic

36
Q

What are the 2 ways that monozygotic twins may be produced?

A

1) Initial cleavage after fertilisation causes the zygote to completely split, forming 2 embryos, with separate membranes and placenta’s
2) Two inner cell masses form in one blastocyst, forming 2 embryos with the same membranes and placenta

37
Q

What process may produce conjoined twins?

A

When two inner cell masses form in one blastocyst, as the 2 embryos will form from the same membranes, which may not complete separation before birth

38
Q

Will conjoined twins always be identical, and why (not)?

A

Yes, as they form from the same zygote, sharing the placenta and amniotic sac

39
Q

Define teratogenesis:

A

The process by which normal embryonic development is disrupted, leading to congenital malformations.

40
Q

Which period of embryonic development is most sensitive to teratogenesis?

A

Embryonic (weeks 3-8)

41
Q

What is a teratogen?

A

An agent or factor which causes malformation of an embryo, by interfering with development

42
Q

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

A

If teratogenesis occurs here, death of the embryo and abortion occurs.

43
Q

Name 3 main teratogens:

A

1) Thalidomide
2) Alcohol
3) Rubella

ESA1 (22 decks)

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