11. Embryology 2 Flashcards

1
Q

What happens in the embryonic period?

A

All major structures (limbs) and systems are formed

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2
Q

When and where does the primitive streak appear?

A

In week 3

Appears on dorsal surface of epiblast

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3
Q

What are the 2 main steps in gastrulation?

A

Migration and invagination

Displacement of hypoblast and creation of third layer

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4
Q

What happens in migration and invagination?

A

Epiblast cells push through epithelial layer

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5
Q

What happens in displacement of hypoblast?

A

3rd layer is formed
Becomes trilaminar disc
Holes from in mesoderm which will layer become mouth and anus

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6
Q

What are the 3 layers that are created in gastrulation?

A

Ectoderm
Mesoderm
Endoderm

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7
Q

What does the ectoderm form into?

A

Organs and structures that maintain contact with outside world
E.g. nervous system, epidermis

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8
Q

What does the mesoderm form into?

A

Supporting tissues

E.g. muscle, cartilage, bone, vascular system

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9
Q

What does the endoderm form into?

A

Internal structures

E.g. epithelial lining of GI tract, respiratory tract, parenchyma of glands

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10
Q

When does gastrulation occur?

A

Week 3 of development

Start of embryonic period

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11
Q

What happens in gastrulation?

A

Bilaminar disc converted to trilaminar disc

3 germ layers: ectoderm, mesoderm, endoderm

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12
Q

How does gastrulation occur?

A

Primitive streak forms in caudal epiblast, leads to migration and invagination of epiblast cells

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13
Q

Why does gastrulation occur?

A

Ensure correct placement of precursor tissues to allow subsequent morphogenesis

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14
Q

What is the notochord and when is it formed?

A

Solid rod of cells running in midline with important signalling role
Formed in neurulation

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15
Q

What does the notochord do?

A

Releases chemicals so ectoderm can respond, responds by thickening

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16
Q

What are somites?

A

Organisation of parasail mesoderm into segments
First pair appear at day 20 in occipital region
Appear 3 pairs/day until 42-44 pairs present

17
Q

How many somites are there in total at the end?

A

31, therefore 31 pairs of spinal nerves

18
Q

What happens in organised degeneration of somites?

A

Ventral wall of somite breaks down leaving to formation of sclerotome
Further organisation of dorsal portion forms combined dermomyotome

19
Q

What happens to the myotome?

A

Proliferates and migrates

Dermatologist disperses

20
Q

What does the dermatome later form?

A

Skin section, dermis

21
Q

What does the myotome late form?

A

Muscle section, muscles

22
Q

What does the sclerotome later form?

A

Hard tissue section, bones

23
Q

What does the organisation of mesoderm into somites give rise to?

A

Repeating structures

E.g. vertebrae,ribs, intercostal muscles, spinal cord segments

24
Q

What is the order of folding?

A

Head fold
Tail fold
Lateral folding

25
What does folding achieve?
Creates ventral body Pulls amniotic membrane around disc Embryo becomes suspended in amniotic sac Pulls connecting stalk ventrally
26
What has happened by the end of week 4?
Nervous system started to form Segments appeared, assigning specific tasks to specific cells Embryo folded, putting everything in right place