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Development and Ageing > Early Foetal Development > Flashcards

Early Foetal Development Flashcards

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1
Q

fertilisation age

A

measured from the time of fertilization (assumed to be +1 day from last ovulation)
difficult to know time of fertilization exactly (unless IVF)

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2
Q

gestational age

A

calculated from the time of the beginning of the last menstrual period (LMP)
Determined by fertilization date (+14 days) if known, or early obstetric ultrasound and comparison to embryo size charts.

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3
Q

carnegie stage

A

23 stages of embryo development based on embryo features not time
Allows comparison of developmental rates between species
Covers the window of 0-60 days fertilization age in humans

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4
Q

embryogenic stage is in what trimester?

A

first

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5
Q

When is the embryogenic stage?

A

14-16 days post fertilisation

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6
Q

What happens in the embryogenic stage?

A

establishing the early embryo from the fertilized oocyte
Determining two populations of cells: pluripotent embryonic cells (contribute to fetus)
Extraembryonic cells (contribute to the support structures eg placenta)

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7
Q

embryonic stage is in what trimester?

A

first

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8
Q

when is the embryonic stage?

A

16-50 days post fertilisation

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9
Q

What happens in the embryonic stage?

A

Establishment of the germ layers and differentiation of tissue types
Establishment of the body plan

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10
Q

fetal stage is in what trimester?

A

second and third

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11
Q

when is the fetal stage?

A

8 to 38 weeks

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12
Q

What happens in the fetal stage?

A

Major organ systems now present
Migration of some organ systems to final location
Extensive growth and acquisition of fetal viability (survival outside the womb)

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13
Q

outline the journey from fertilisation to developing into blastocyst

A

ovulated oocyte > zygote > cleavage stage embryos (2-8 cells) > morula (16+ cells) > blastocyst (200-300 cells)

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14
Q

The genes of the embryo are not transcribed until?

A

4-8 cell stage

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15
Q

The embryo is dependent on what to get through the first divisions?

A

maternal mRNAs and proteins

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16
Q

What occurs in the maternal-to-zygotic transition?

A

transcription of embryonic genes, increased protein synthesis, organelle maturation

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17
Q

Compaction starts the?

A

formation of the first two cell types

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18
Q

When does compaction occur?

A

3-4 days post fertilisation

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19
Q

What is compaction?

A

outer cells become pressed against the zona, change from spherical to wedge shaped, outer cell connect via tight gap ix/desmosomes, become polarised, form diffusion barrier

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20
Q

Blastocyst formation establishes what two cell types?

A

pluripotent embryonic cells that contribute to final organism, extra embryonic cells that contribute to the structures that support development

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21
Q

What is the zona pellucida?

A

hard protein shell inhibiting polyspermy and protects the early embryo

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22
Q

What is the blastocoel?

A

fluid filled cavity formed osmotically by trophoblast pumping Na+ ions into cavoty

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23
Q

What is the trophoectoderm?

A

where the extra embryonic cells are

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24
Q

What process does the blastocyst go through to implant?

A

hatching (day 5-6), must escape zona pellucida

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25
How does the blastocyst escape the zona pellucida?
enzymatic digestion | cellular contraction
26
Morula is separated into?
inner cell mass | trophoectoderm
27
trophoblast cells fuse to form?
syncitiotrophoblast
28
What does syncitiotrophoblast invasion cause?
destroys local maternal cells in the endometrium > creates interface between the embryo and the maternal blood supply
29
Why do cytotrophoblast cells remain individual?
to provide a source of syncitiotrophoblast cells
30
Inner cells mass further separates into?
epiblast | hypoblast
31
What is the epiblast?
where the fetal tissues are derived
32
What is the hypoblast?
this forms the yolk sac (extraembryonic structure)
33
What is the final stage before gastrulation?
bi-laminar embryonic disc formation
34
When does bi-laminar embryonic disc formation occur?
day 12+
35
some cells become separated from the epiblast to form what?
amniotic cavity
36
syncitiotrophoblast secretes what important hormone? why is it important?
hCG > important for pregnancy testing
37
What is gastrulation?
differentiation of bi laminar disc into three germ layers
38
When does gastrulation happen?
day 15
39
the development of what determines the axis of the embryo?
primitive streak
40
The primitive streak expands at _____ to create the ________.
``` cranial end primitive node (contains depression called primitive pit > primitive groove) ```
41
After formation of the primitive groove, outline the process that occurs?
invagination >epiblast cells migrate to primitive streak > invasion of hypoblast > displacement of the cells > replaced by definitive endoderm
42
After formation of the definitive endoderm, the remaining cells of the epiblast are referred to as?
ectoderm (most exterior distal layer)
43
Germ layer between endoderm and ectoderm is called?
mesoderm
44
What organs are derived from the endoderm?
``` GI tract liver pancreas lung thyroid ```
45
What organs are derived from the ectoderm?
CNS and neural crest skin epithelia tooth enamel
46
What organs are derived from the mesoderm?
blood (endothelial, RBC, WBC) muscle (smooth, skeletal, cardiac) gonads, kidneys, adrenal cortex, bone, cartilage
47
When does notochord formation occur?
day 13+
48
What is notochord?
rod-like tube structure formed of cartilage-like cells
49
Where is the notochord found?
along the embryo midline under the ectoderm
50
The notochord acts as?
a key organizing centre for neurulation and mesoderm development
51
What is the neural plate?
thickened ectoderm
52
What is neurulation?
forming the neural tube and CNS
53
Outline what happens in neurulation.
neural plate invaginates > forms groove > creates two ridges (neural folds) > neural crest cells specified in folds > folds fuse > overlaid with ectoderm > migration of neural crest cells from folds
54
The neural folds run along what?
cranio-caudal axis
55
The neural tube is initially open at each end. When does the head end close?
day 23
56
The neural tube is initially open at each end. When does the tail end close?
day 27
57
Closure of the head end of the neural tube precedes the formation of?
brain structures
58
List examples of neural tube defects.
anencephaly | spina bifida
59
What is anencephaly?
(absence of most of the skull and brain) arises from failure to close at the head end
60
What is spina bifida?
(open neural tube at birth, usually lower spine due to failure to close tail end– varying severity
61
Neural crest cells
Ectoderm-derived, plastic and migrate extensively during development
62
List types of neural crest migration
cranial NC cardiac NC trunk NC vagral and sacral NC
63
cranial neural crest cells specify to?
cranial neurones, glia, lower jaw, middle ear bones (ossicles), facial cartilage
64
cardiac neural crest cells specify to?
aortic arch/pulmonary artery septum, large arteries wall musculoconnective tissue
65
trunk neural crest cells specify to?
dorsal root ganglia, sympathetic ganglia, adrenal medulla, aortic nerve clusters, melanocytes
66
vagral and sacral neural crest cells specify to?
parasympathetic ganglia and enteric nervous system ganglia
67
Defects of neural crest migration/ specification lead to birth defects including?
pigmentation disorders deafness cardiac and facial defects and failure to innervate the gut
68
what is somitogenesis?
formation of somites
69
what are somites?
arise from paired blocks of paraxial mesoderm flanking the neural tube and notochord
70
outline somitogenesis
Blocks of paraxial mesoderm condense and bud off in somite pairs > One of each either side of the neural tube > commences at the head end + progresses down
71
how many somite pairs in humans/rate of budding?
44 pairs | 1 pair/90 minutes
72
Somites form what two types of embryonic tissue?
sclerotome | dermomyotome
73
sclerotome forms?
vertebrae and rib cartilage
74
dermomyotome sub divides to form?
dermatome | myotome
75
dermatome gives rise to?
dermis of the skin | some fat + connective tissues of neck and trunk
76
myotome gives rise to?
muscles of the embryo
77
when does formation of the gut tube occur?
day 16+
78
the primitive gut arises from what types of folding?
ventral folding | lateral folding
79
the folding _____________ to form the primitive gut.
pinches off part of the yolk sac
80
primitive gut is patterned into?
foregut midgut hindgut
81
foregut derivatives
oesophagus, stomach, upper duodenum, liver, gallbladder, pancreas
82
midgut derivatives
lower duodenum and remainder of small intestine, ascending colon and first two-thirds of transverse colon
83
hindgut derivatives
last third of the transverse colon, descending colon, rectum and upper anal canal
84
heart begins pumping blood around?
day 22 (detectable about 6 weeks gestational age)
85
when do lungs arise? split into two?
4th week end of 4th week continues to branch throughout development
86
how do gonads arise?
bipotential structures (gonadal/genital ridges) > specify into male/female genitals
87
how do XY embryos develop gonads?
presence of SRY gene on Y chromosome > gonadal cells become Sertoli cells > triggers testis development, Leydig cell formation, testosterone production
88
how do XX embryos develop gonads?
absence of SRY gene > gonadal cells adopt granulosa cell fate + ovary development
89
ovary development requires reinforcement by?
FOXL2

Development and Ageing (9 decks)

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