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ESA 1 - RJS > Embryology > Flashcards

Embryology Flashcards

1
Q

What surrounds the blastomeres after first mitotic divide?

A

Zona pellucida

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2
Q

When does the first mitotic divide occur?

A

30 hours after fertisilation

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3
Q

What is created in day 3?

A

Morula - totipotent cells

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4
Q

What happens to the morula?

A

Compaction occurs to create blastocyst (formation of first cavity)

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5
Q

What are the four components of the blastocyst?

A

Zona pellucida
Outer cell mass - trophoblast
Inner cell mass - embryoblast
Blastocyst cavity

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6
Q

What occurs after the formation of the blastocyst?

A

Hatching from zona pellucida

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7
Q

After implantation begin, what occurs?

A

Formation of bilaminar disc

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8
Q

What does the embryoblast form?

A

Epiblast and hypoblast

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9
Q

What does the trophoblst form?

A

Cytotrophoblast and syncytiotrophoblast

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10
Q

Name the components present after the formation of the bilaminar disc

A

Epiblast, hypoblast - forming bilaminar disc
Cytotrophoblast, synctiotrophoblast
Amniotic cavity
Blastocyst cavity

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11
Q

What occurs after the formation of the bilaminar disc?

A

Formation of primitive yolk sac by hypoblast development

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12
Q

What happens to the primitive yolk sac that is connected to the cytotrophoblast?

A

It is pushed away from the cytotrophoblast

Extraembryonic mesoderm fills its place

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13
Q

What occurs after primitive yolk sac is pushed away from cytotrophoblast?

A

Uteroplacental circulation begins

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14
Q

How does uteroplacental circulation occur?

A

Invasion of maternal sinusoid to syncytiotrophoblast

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15
Q

What occurs after uteroplacental circulation?

A

Formation of secondary yolk sac

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16
Q

How does the secondary yolk sac form?

A

Pinches off from primitive yolk sac

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17
Q

In terms of embryology, what is the present at the end of week 2?

A 
Bilaminar disc composed of epiblast and hypoblast
Amniotic cavity of epiblast cells
Primary yolk sac of hypoblast cells
Secondary yolk sac of hypoblast cells
Chorionic cavity
Connecting stalk
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18
Q

Where is the ideal location of implantation?

A

Posterior uterine wall

19
Q

What is the different between topipotent and pluripotent cells? When does the change occur?

A

Totipotent - capacity to become anything
Pluripotent - capacity to become one of many cell types
Change occurs during compaction

20
Q

What occurs during gastrulation?

A

Process of establishing the 3 germ layers (trilaminar disc)

Sets axes

21
Q

From where does the primitive streak develop?

A

Develops from caudal end of epiblast layer

22
Q

Describe the formation of the primitive streak, node and pit

A

The primitive streak is a narrow groove with bulging edges

The primitive node is at the end with the pit lying between it and the streak

23
Q

What occurs after the formation of the primitive streak, node and pit?

A

Migration and invagination of epiblast layer, spreading laterally and cephalad between epiblast and hypoblast
Displacement of the hypoblast layer with creation of third layer
Trilaminar disc is formed

24
Q

What are the 3 layers of the trimlaminar disc?

A

Ectoderm
Mesoderm
Endoderm

25
Q

Describe the formation of the notochord

A

Prenotochordal cells of the spiblast migrate through the cranial part of the primitive pit to form solid rod of cells

26
Q

Why is the notochord important?

A

Defines midline
Axial skeleton forms around it
Drives neurulation

27
Q

Why is the primitive node important?

A

Emits molecular signals which ensure correct dorso-ventral and left-right orientation

28
Q

What is ultimately derived from the ectoderm?

A

Organs and structures with contact to the outside world (nervous, epidermis)

29
Q

What is ultimately derived from the mesoderm?

A

Supporting tissues (muscles, cartilage, bone & vascular system)

30
Q

What is ultimately derived from the endoderm?

A

Internal structures (GI, respiratory & urinary tract)

31
Q

How is left and right asymmetry formed?

A

Action of cilated cells at node results in leftward flow of signalling molecules - side specific signalling cascades initiated

32
Q

What occurs during the fourth week?

A

Neurulation
Mesoderm differentiation
Folding

33
Q

What is neurulation?

A

Notochord driven induction of ectoderm to form nervous system

34
Q

How does neurulation occur?

A

Notochord signals for overlying ectoderm to thicken to form neural plate
Edges elevate out of plane of disc and then curl towards each other to form neural tube

35
Q

What is the first step in mesoderm diffrentiation?

A

Mesoderm organises into paraxial mesoderm, lateral mesoderm (somatic mesoderm, splanchnic mesoderm) and intermediate mesoderm

36
Q

What does the paraxial mesoderm form?

A

Somites which develop craniocaudal - 31 pairs

37
Q

Describe organised degeneration of the somite

A

Degeneration of the ventral wall of somite forms sclerotome
Further organisation occurs to form combined dermomyotome
Myotome proliferates and migrates and dermatome disperses

38
Q

What do the dermatome, myotome and sclerotome give rise to?

A

Dermatome - Skin section (dermis)
Myotome - Muscle section (muscle)
Sclerotome - Hard tissue (bone)

39
Q

What do somites ultimately give rise to?

A

Repeating structures e.g. vertebrae, ribs, intercostal muscles, spinal cord segments
Also guides innervation

40
Q

What does the paraxial mesoderm ultimately give rise to?

A

Axial skeleton, dermis, muscles

41
Q

What does the intermediate mesoderm ultimately give rise to?

A

Urogenital system

42
Q

What does the lateral mesoderm ultimately give rise to?

A

Somatic - connective tissues of limbs

Splanchnic - Smooth masculature, connective tissue and vascularture of gut

43
Q

How does the embryo fold?

A

Driven by lateral plate mesoderm pulling downwards and encompassing all the primitive yolk sac creating the embryo suspended within aminotic sac

ESA 1 - RJS (6 decks)

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