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Early embryology Flashcards

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1
Q

What creates a zygote?

A

Fertilisation between female oocyte and male sperm

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2
Q

What happens to zygote?(think expansion)

A

Mitotic cell divisions (cleavage) making daughter cells (blastomeres)

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3
Q

What are blastomeres?

A

Daughter cells formed during cleavage of zygote

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4
Q

What surrounds the oocyte?

A

Thick glycoprotein layer called the zona pellucida

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5
Q

What does sperm bind to?

A

Zona glycoprotein, ZP3, is responsible for sperm binding

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6
Q

How do sperm degrade the ZP?

A

Once bound to ZP3 they undergo an acrosome reaction which produces enzymes that can degrade the ZP.

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7
Q

At what cell stage of cleavage do cells lose their totipotency?

A

16 cell

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8
Q

What stages of the cell cycle do not occur in cleavage?

A

G1/G2

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9
Q

What is the cell mass called at the 16 cell stage?

A

Morula

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10
Q

What is compaction, what does it do?

A

TJs form between the cells, blastomeres align, separates inner cells from outer cells

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11
Q

What is the inner cell mass and the outer cell mass called?

A

Inner cell mass - embryoblast

Outer cell mass - trophoblast

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12
Q

What does inner cell mass do?

A

Form embryo proper

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13
Q

What does outer cell mass form?

A

Contributes to placenta

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14
Q

What causes Inner cell mass to be displaced to one side (what’s this side called)?

A

Fluid accumulation collecting in blastocele cavity - flattens inner cell mass into embryonic pole/embryoblast

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15
Q

What is the blastocele?

A

A fluid cavity that forms in the intracellular spaces of the inner cell mass

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16
Q

When is implantation?

A

Day 6

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17
Q

What happens to uterus after implantation?

A

Endometrial cells adjacent to implanted blastocyst undergo decidual reaction

Uterine lining becomes swollen and vascular - trigger secretion of GFs, glycogen and mucus

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18
Q

What is the decidual reaction?

A

Causes uterine lining adjacent to implanted embryo to become swollen and vascular - trigger secretion of GFs, glycogen and mucus

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19
Q

What happens to the trophoblast layers after implantation?

A

Trophoblast differentiates into two layers, invade uterine wall

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20
Q

What are the two populations of trophoblast?

A

Inner layer of mononuclear cells (cytotrophoblast)

Highly invasive outer layer with no cell boundaries (syncytiotrophoblasts)

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21
Q

What sort of trophoblastic cells make hCG?

A

Syncytiotrophoblast

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22
Q

What does hCG do?

A

Maintain corpus luteum

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23
Q

What combine to form placenta?

A

Trophoblasts and uterine tissue

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24
Q

When is implantation complete?

A

Day 13

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25
What is an ectopic pregnancy (where do most occur)?
Implant outside of uterus (mostly in uterine tube)
26
What do trophoblasts do after invading uterine wall (i.e. ECM)?
Break down ECM between endometrial cells
27
What is the cellular difference between cytotrophoblast and syncytiotrophoblast?
Cytotrophoblast is mitotic Syncytiotrophoblast is multinucleate
28
Describe what happens to inner cell mass during implantation?
Differentiate into epiblast and hypoblast
29
What is hypoblast adjacent to?
Blastocele/blastocyst cavity
30
What cell shapes are the epiblast vs hypoblast?
Hypoblast (cuboidal) Epiblast (columnar)
31
Where does amniotic cavity form?
Epiblast, splits it into two layers
32
What happens to epiblast layer after it's split by amniotic cavity?
Epiblast layer adjacent to cyotrophoblasts will form amnion
33
What does amnion do?
Lines amniotic cavity and eventually envelops embryo
34
What compromises bilaminar germ disc?
External epiblast | Hypoblast
35
When does the bilaminar germ disc form?
Week 2
36
What do cells from hypoblast do?
Migrate to form extraembeyonic endoderm and mesoderm (not part of embryo)
37
What do extraembryonic endoderm and extraembryonic mesoderm do?
Migrate from hypoblast to line blastocele cavity which converts cavity to primary yolk sac then secondary yolk sac
38
How does the blood supply to the syncytiotrophobast originate?
Vesicles present in the syncytiotrophoblast fuse forming large lacunae Lacunae become continuous with maternal capillaries (which when dilated become known as sinusoids), maternal blood then enters the lacunae.
39
As placenta develops how does cytotrophoblast develop?
Cytotrophoblast develops increasing levels of villi invaginating into the syncytiotrophoblast
40
Extra-embyronic mesoderm lining cytotrophoblast and amnion is?
Extra embryonic somatic mesoderm
41
Extra-embyronic mesoderm lining covering yolk sac is?
Extra-embyronic splanchnic mesoderm
42
Compare speeds of bilaminar disc comparted to trophoblast?
Growth of bilaminar disc slow compared to trophoblast
43
Cavities form in the extraembryonic mesoderm, they?
Develop/join form chorionic/extraembryonic cavity
44
What does extraembryonic cavity surround, what's the exception?
Prim yolk sac and amniotic cavity except where germ disc connected to trophoblast by connecting stalk
45
Which 2 cavities form in week 2?
Amniotic and yolk sac cavities
46
How does umbilical cord form?
Embryo attached to its trophoblastic shell by connecting stalk, stalk develops into umbilical cord
47
What does gastrulation achieve?
3 germ layers established and basic body plan emerges.
48
When does gastrulation occur?
3rd week
49
How does gastrulation start?
Formation of midline structure primitive streak in epiblast
50
What end of bilaminar embryo disc is prim streak found?
Caudal end
51
What does primitive streak define?
Rostral caudal axis Left right axis Dorsal ventral axis
52
Where does primitive node develop relative to prim streak?
Rostral end of prim streak
53
What does primitive node do?
Neural inducing and organising properties.
54
Where do epiblast cells move (through) in gastrulation?
Primitive streak
55
What do first and second wave of epiblastic cells form?
First wave: displace hypoblast creates embryonic endoderm 2nd wave: spreads between endoderm and epiblast forms embryonic mesoderm
56
How is embryonic ectoderm formed from epiblast?
Epiblast cells that don't go through streak
57
What structures does ectoderm form?
Skin and CNS
58
What does non neural ectoderm form?
Skin, tooth enamel, nails
59
What does mesoderm form?
Skeletal and connective tissue, blood and muscle
60
What are the 2 types of mesoderm?
Axial mesoderm and paraxial mesoderm
61
What does notochord do?
Pattern other structures
62
What stage of development does the notochord form in?
Gastrulation
63
What cells form the notochord?
Endoderm and hypoblast
64
How is the notochord formed?
Cells of the notochordal plate (hypoblast and endoderm) detach from the endoderm forming a solid cord of cells.
65
What does the notochord eventually become?
Nucleus palposus of the spine
66
What does paraxial mesoderm form in trunk?
37 pairs of somites
67
What does paraxial mesoderm form in head?
Somitomeres - contribute to head mesenchyme (i.e. muscles of face and bones of skull)
68
What does paraxial mesoderm do either side of notochord?
Condenses into segments
69
What are somites?
Paired balls of paraxial mesoderm
70
What do somites differentiate into?
Sclerotome | Dermamyotome (dermatome and myotome)
71
What part of somite is sclerotome formed from?
Ventromedial parts of somite
72
What do sclerotome cells do (where do they move and form)?
``` Move medially forming: Vertebral body (surrounding notochord) ``` Verebral arch (surrounds neural tube) Annulus fibrosis Ribs
73
What does dermatome contribute to?
Dermis (fat and connective tissue of neck and back)
74
What does myotome differentiate to?
Muscle
75
What does intermediate mesoderm do?
Differentiate into urogenital structures
76
What does lateral plate mesoderm line?
Divide to line intraembryonic coelom
77
What does lateral plate mesoderm form?
Somatic/parietal mesoderm Splanchnic /visceral mesoderm
78
What is somatic/parietal mesoderm adjacent to?
Ectoderm
79
What does splanchnic/visceral mesoderm do?
Forms gut wall and vascular system
80
What is splanchnic mesoderm adjacent to?
Endoderm
81
What does somatic/parietal mesoderm form?
Dermis and limbs
82
Where is mesoderm absent in body (2 points) i.e. endoderm direct contact with ectoderm?
Buccopharngeal membrane (rostrally) and cloacal membrane (caudal)
83
What do buccopharyngeal membrane and cloacal membrane mark?
End of gut tube
84
Each somite forms its own...
Sclerotome, myotome and dermatome
85
Each myotome and dermatome retains its...
Innervation from its segment of origin regardless of where they migrate
86
What does endoderm form?
Gut tube, liver, lungs
87
How does notochord pattern neural tube?
Shh, pattern along dorsal ventral axis
88
What is a teratogen?
Substance that causes malformation in embryo/fetus
89
What is a critical period?
Period of development during which organ/system is susceptible to genetic/environmental factors
90
When generally is the most sensitive period for teratogenic effects?
3-8 weeks
91
Does a teratogen always have an effect on embryonic development, why?
No, teratogen may be administered before/after critical sensitive period
92
What is situs inversus?
Position of major organs is reversed
93
What axis of embryonic disc grows in gastrulation?
Rostral caudal axis
94
What direction do cells migrate to form primitive streak?
Rostrally
95
In what direction does primitive streak shorten/regress?
Towards caudal end
96
How does sclerotome fuse to form vertebrae?
The lower half of one sclerotome fuses with the upper half of the adjacent one to form each vertebral body.
97
Embryonic germ layer from which the notochord is derived
Epiblast
98
What can the notochord be classed as?
Mesoderm (axial)
99
Embryonic ectoderm gives rise to the...
Brain
100
Does the trophoblast become anything to do with the foetus?
No

Embryology (10 decks)

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