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Development and Ageing > Early Foetal Development > Flashcards

Early Foetal Development Flashcards

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
Q

How does the blastocyst escape the zona pellucida?

A

enzymatic digestion

cellular contraction

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26
Q

Morula is separated into?

A

inner cell mass

trophoectoderm

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27
Q

trophoblast cells fuse to form?

A

syncitiotrophoblast

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28
Q

What does syncitiotrophoblast invasion cause?

A

destroys local maternal cells in the endometrium > creates interface between the embryo and the maternal blood supply

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29
Q

Why do cytotrophoblast cells remain individual?

A

to provide a source of syncitiotrophoblast cells

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30
Q

Inner cells mass further separates into?

A

epiblast

hypoblast

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31
Q

What is the epiblast?

A

where the fetal tissues are derived

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32
Q

What is the hypoblast?

A

this forms the yolk sac (extraembryonic structure)

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33
Q

What is the final stage before gastrulation?

A

bi-laminar embryonic disc formation

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34
Q

When does bi-laminar embryonic disc formation occur?

A

day 12+

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35
Q

some cells become separated from the epiblast to form what?

A

amniotic cavity

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36
Q

syncitiotrophoblast secretes what important hormone? why is it important?

A

hCG > important for pregnancy testing

37
Q

What is gastrulation?

A

differentiation of bi laminar disc into three germ layers

38
Q

When does gastrulation happen?

A

day 15

39
Q

the development of what determines the axis of the embryo?

A

primitive streak

40
Q

The primitive streak expands at _____ to create the ________.

A 
cranial end
primitive node (contains depression called primitive pit > primitive groove)
41
Q

After formation of the primitive groove, outline the process that occurs?

A

invagination >epiblast cells migrate to primitive streak > invasion of hypoblast > displacement of the cells > replaced by definitive endoderm

42
Q

After formation of the definitive endoderm, the remaining cells of the epiblast are referred to as?

A

ectoderm (most exterior distal layer)

43
Q

Germ layer between endoderm and ectoderm is called?

A

mesoderm

44
Q

What organs are derived from the endoderm?

A 
GI tract
liver
pancreas
lung
thyroid
45
Q

What organs are derived from the ectoderm?

A

CNS and neural crest
skin epithelia
tooth enamel

46
Q

What organs are derived from the mesoderm?

A

blood (endothelial, RBC, WBC)
muscle (smooth, skeletal, cardiac)
gonads, kidneys, adrenal cortex, bone, cartilage

47
Q

When does notochord formation occur?

A

day 13+

48
Q

What is notochord?

A

rod-like tube structure formed of cartilage-like cells

49
Q

Where is the notochord found?

A

along the embryo midline under the ectoderm

50
Q

The notochord acts as?

A

a key organizing centre for neurulation and mesoderm development

51
Q

What is the neural plate?

A

thickened ectoderm

52
Q

What is neurulation?

A

forming the neural tube and CNS

53
Q

Outline what happens in neurulation.

A

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
Q

The neural folds run along what?

A

cranio-caudal axis

55
Q

The neural tube is initially open at each end. When does the head end close?

A

day 23

56
Q

The neural tube is initially open at each end. When does the tail end close?

A

day 27

57
Q

Closure of the head end of the neural tube precedes the formation of?

A

brain structures

58
Q

List examples of neural tube defects.

A

anencephaly

spina bifida

59
Q

What is anencephaly?

A

(absence of most of the skull and brain) arises from failure to close at the head end

60
Q

What is spina bifida?

A

(open neural tube at birth, usually lower spine due to failure to close tail end– varying severity

61
Q

Neural crest cells

A

Ectoderm-derived, plastic and migrate extensively during development

62
Q

List types of neural crest migration

A

cranial NC
cardiac NC
trunk NC
vagral and sacral NC

63
Q

cranial neural crest cells specify to?

A

cranial neurones, glia, lower jaw, middle ear bones (ossicles), facial cartilage

64
Q

cardiac neural crest cells specify to?

A

aortic arch/pulmonary artery septum, large arteries wall musculoconnective tissue

65
Q

trunk neural crest cells specify to?

A

dorsal root ganglia, sympathetic ganglia, adrenal medulla, aortic nerve clusters, melanocytes

66
Q

vagral and sacral neural crest cells specify to?

A

parasympathetic ganglia and enteric nervous system ganglia

67
Q

Defects of neural crest migration/ specification lead to birth defects including?

A

pigmentation disorders
deafness
cardiac and facial defects and failure to innervate the gut

68
Q

what is somitogenesis?

A

formation of somites

69
Q

what are somites?

A

arise from paired blocks of paraxial mesoderm flanking the neural tube and notochord

70
Q

outline somitogenesis

A

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
Q

how many somite pairs in humans/rate of budding?

A

44 pairs

1 pair/90 minutes

72
Q

Somites form what two types of embryonic tissue?

A

sclerotome

dermomyotome

73
Q

sclerotome forms?

A

vertebrae and rib cartilage

74
Q

dermomyotome sub divides to form?

A

dermatome

myotome

75
Q

dermatome gives rise to?

A

dermis of the skin

some fat + connective tissues of neck and trunk

76
Q

myotome gives rise to?

A

muscles of the embryo

77
Q

when does formation of the gut tube occur?

A

day 16+

78
Q

the primitive gut arises from what types of folding?

A

ventral folding

lateral folding

79
Q

the folding _____________ to form the primitive gut.

A

pinches off part of the yolk sac

80
Q

primitive gut is patterned into?

A

foregut
midgut
hindgut

81
Q

foregut derivatives

A

oesophagus, stomach, upper duodenum, liver, gallbladder, pancreas

82
Q

midgut derivatives

A

lower duodenum and remainder of small intestine, ascending colon and first two-thirds of transverse colon

83
Q

hindgut derivatives

A

last third of the transverse colon, descending colon, rectum and upper anal canal

84
Q

heart begins pumping blood around?

A

day 22 (detectable about 6 weeks gestational age)

85
Q

when do lungs arise? split into two?

A

4th week
end of 4th week
continues to branch throughout development

86
Q

how do gonads arise?

A

bipotential structures (gonadal/genital ridges) > specify into male/female genitals

87
Q

how do XY embryos develop gonads?

A

presence of SRY gene on Y chromosome > gonadal cells become Sertoli cells > triggers testis development, Leydig cell formation, testosterone production

88
Q

how do XX embryos develop gonads?

A

absence of SRY gene > gonadal cells adopt granulosa cell fate + ovary development

89
Q

ovary development requires reinforcement by?

A

FOXL2

Development and Ageing (9 decks)

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