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brs 1: development & aging domain > 1.2: Early fetal development > Flashcards

1.2: Early fetal development Flashcards

1
Q

Fertilisation age (conceptual age)

A

Measured from time of fertilisation
Difficult to know exact time - 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 fertilisation date (+14 days ) if known, or early obstetric ultrasound and comparison to embryo size charts

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3
Q

Carnegie stage

A

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

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4
Q

How many stages of embryo development are there and what determines them

A

23 stages
Dependent on embryo features not time - carnegie stage

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5
Q

Stages of embryo-fetal development

A

Embryogenic stage 14-16 days post fertilisation
Embryonic stage 16-50 days post fertilisation
Foetal stage 50-270 days post fertilisation

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6
Q

What occurs during the Embryogenic stage

A

Establishing the early embryo from fertilised oocyte - embryo genesis
Determining two populations of cells : pluripotent embryonic cells, extraembryonic cells

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7
Q

What do pluripotent embryonic cells contribute to

A

Foetus

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8
Q

What do Extraembryonic cells contribute to

A

Support structures e.g. placenta

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9
Q

When does the Embryonic stage occur

A

16-50 days post fertilisation

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10
Q

What occurs in the Embryonic stage

A

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

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11
Q

Fetal stage occurs

A

50-270 days post-fertilisation (8-38 weeks)

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12
Q

What happens in the fetal stage

A

Major organ systems present
Migration of some organ systems to final location
Extensive growth and acquisition of fetal viability - survival outside of womb

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13
Q

First trimester is composed of

A

Embryogenic stage
Embryonic stage

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14
Q

Second and third trimester is composed of

A

Fetal stage

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15
Q

4 Stages of the first few days of life following fertilisation

A

Zygote (1 cell)
Cleavage stage embryos (2-8 cells) : mitotic divisions
Morula (16+ cells) : further mitiotic divisions
Blastocyst (200-300 cells)

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16
Q

What are the genes like in an embryo until the 4-8 cell stage

A

Genes not transcribed
Embryo dependent on maternal mRNSa and proteins to get through first divisions
MRNA and proteins synthesised and stored during oocyte development

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17
Q

What can failure to synthesise, store or interpret mRNAs and proteins during oogenesis lead to

A

May impair embryonic development

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18
Q

Maternal-to-zygotic transition (4-8 cell stage)

A

MZT - embryonic genome activation
Transcription of embryonic genes (zygotic genome activation- not maternal genome)

Increases protein synthesis
Organelle maturation (mitochondria, Golgi)

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19
Q

What starts the formation of the first two cell types

A

Compaction

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20
Q

What change of shape occurs around the 8-cell stage or later

A

Change from spherical to wedge-shaped

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21
Q

What happens to outer cells around the 8-cell stage or later

A

Outer cells become pressed against zona
connect each other through tight gap junctions and desmosomes
Forms barrier to diffusion between inner and outer embryo
Outer cells become polarised

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22
Q

What does blastocyst formation establish

A

Two cell types

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23
Q

The blastocoel of a blastocyst is

A

Fluid-filled cavity formed osmotically by trophoblast pumping Na+ ions into cavity

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24
Q

The zona pellucida of the blastocyst is

A

Hard protein shell inhibiting polyspermy and protecting early embryo

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25
Q

Characteristics of the inner cell mass of a blastocyst

A

Pluripotent embryonic cells that contribute to final organism

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26
Q

Characteristics of the trophoectoderm

A

Extra-embryonic cells that contribute to the extraembryonic structures that support development

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27
Q

What happens to the blastocyst during hatching (day 5-6)

A

To implant, the blastocyst must escape zona pellucida
Enzymatic digestion
Cellular contractions

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28
Q

Separation of embryonic cell lineages I

A

Morula separates into :
1) inner cell mass (embryonic)
2) trophectoderm (extra-embryonic)

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29
Q

In peri-implantation (day 7-9) Trophoectoderm lineage separates further :

A

Trophoblast cells fuse to form syncitiotrophoblast
Syncitiotrophoblast invasion destroys local maternal cells in the endometrium
Creates interface between embryo and maternal blood supply
Cytotrophoblast cells remain individual to provide source of syncitiotrophoblast cells

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30
Q

In peri-implantation (day 7-9) inner cell mass separates further into:

A

Epiblast: from which foetal tissues will be derived
Hypoblast: which will form the yolk sac (extraembryonic structure)

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31
Q

Separation of embryonic cell lineages 2 : embryonic branch

A

Epiblast and Hypoblast

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32
Q

Separation of embryonic cell lineages 2: extra-embryonic branch

A

Cytotrophoblast, syncitiotrophoblast

33
Q

What is the bi-laminar embryonic disc

A

(Two-layer) embryonic disc is the final stage before gastrulation

34
Q

What happens during the bi-laminar embryonic disc formation (day 12-14)

A

Some cells separated from the Epiblast by the formation of new cavity - amniotic cavity
These amnion cells contribute to extra-embryonic membranes.
This leaves two-layer disc of Epiblast and hypoblast, sandwiched between cavities.
Embryo is now ready for gastrulation

35
Q

What does a Syncitiotrophoblast secrete

A

hCG

36
Q

Extra-embryonic cells differentiate further into

A

Syncitiotrophoblast
Cytotrophoblast

37
Q

Inner cell mass forms

A

Bilaminar disc

38
Q

Formation of the primitive streak defines

A

Head-tail and left-right axes of embryo

39
Q

Invagination of cells into primitive streak forms 3 germ layers:

A

Endoderm cells (first through the streak)
Ectoderm remains on the upper (ventral) surface
Mesoderm sandwiched between ends and ectoderm

40
Q

What 5 organs form the endoderm Germ layer

A

GI tract
Liver
Pancreas
Lung
Thyroid

41
Q

What 4 organs form the ectoderm germ layer

A

CNS
Neutral crest
Skin epithelia
Tooth enamel

42
Q

What 7 organs form the mesoderm germ layer

A

Blood
Muscle
Gonads
Kidneys
Adrenal cortex
Bone
Cartilage

43
Q

What is the notochord

A

Rod-like tube structure formed of cartilage-like cells
Forms along the embryo midline, under the ectoderm
Key organising centre for neurulation and mesoderm development

44
Q

What occurs on days 13-17

A

formation of body plan:
- notochord formation
-neurulation
-somitogenesis
-formation of gut tube

45
Q

What is neurulation

A

Formation of the neural tube and CNS

46
Q

Process of neurulation and neural tube formation

A

1) notochord signals direct neural plate ectoderm to invaginate forming neural groove
2) creates two ridges running along the cranio-caudal axis
3) neural crest cells specified in neural folds
4) neural folds move together over neural groove and fuse forming a hollow tube
5) neural tube overlaid with with epidermis (ectoderm)
6) migration of the neural crest cells form folds

47
Q

At what day does the neural tube close at the head end

A

23
Precedes formation of brain structures

48
Q

At what day does the neural tube close at the tail end

A

27

49
Q

What two developmental defects does failure of neural tube closure cause

A

Anencephaly - absence of most of the skull and brain ; arises from failure close to head end

Spina bifida- open neural tube at birth, usually lower spine due to failure to close tail end

Pigmentation defects, deafness, cardiac and facial defects, gut innervation defects

50
Q

Neural crest cells characteristics

A

Ectoderm-derived, plastic and migrate extensively during development

51
Q

4 neural crest cells

A

Cranial NC
Cardiac NC
Trunk NC
Vagral and Sacral NC

52
Q

Cranial NC give rise to

A

Cranial neurones, glia, lower jaw, middle ear bones, facial cartilage

53
Q

Cardiac NC give rise to

A

Aortic arch, large arteries walls musculoconnective tissue

54
Q

Trunk NC give rise to

A

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

55
Q

Vagral and Sacral NC give rise to

A

Parasympathetic ganglia and enteric nervous system ganglia

56
Q

What do defects of neural crest migration lead to

A

Diverse birth defects; including pigmentation disorders, deafness, cardiac and facial defects, failure to inner age the gut

57
Q

Somitogenesis is

A

Formation of somites

-divide into two :
Sclerotome - bones and rib cartilage
Deermomyotome - dermatome (dermis of skin), myotome (muscles)

58
Q

Somites arise from

A

Paired blocks of paraxial mesoderm flanking the neural tube and notochord
paraxial mesoderm -> condense and bud off into somite pairs
Begins at head end and progresses down 1/90mins in humans (44 total)

59
Q

How do somites form

A

Blocks of paraxial mesoderm condense and bud off in somite pairs
One of each pair either side of the neural tube
Somitogenesis commences at the head end and progresses down the long axis of the embryo
Rate of budding or appearance of somite pairs is species-specific as is the number of pairs

60
Q

Rate of budding in humans

A

1 pair / 80min, 44pairs

61
Q

What two types of embryonic tissue do somites form

A

Sclerotome
Dermomyotome

62
Q

What does Sclerotome tissue form

A

Vertebrae
Rib cartilage

63
Q

What does dermomyotome tissue divide into

A

Dermatology
Myotome

64
Q

What does dermatome give rise to

A

Dermis of the skin, some fat and connective tissues of neck and trunk

65
Q

What does the myotome tissue form

A

Muscles of embryo

66
Q

When is the gut tube formed

A

Day 16+

67
Q

What two types of folding in the embryo give rise to the primitive gut

A

Ventral folding - where the head and tail ends curl together
Lateral folding - where two sides of the embryo roll

68
Q

How is the primitive gut formed

A

Foldings in the gut pinch off part of the yolk sac
Then patterned into foregut, midgut,and hindgut

69
Q

Derivatives of the foregut

A

Esophagus, stomach, upper duodenum, liver, gallbladder, pancreas

70
Q

Derivatives of the midgut

A

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

71
Q

Derivatives of hindgut

A

Last third of transverse colon, descending colon, rectum and upper anal canal

72
Q

How is the heart formed in an embryo

A

Begins as a tube of mesoderm around day 19,
Beating and pumping blood commences day 22
Foetal heartbeat detectable from 6weeks gestational age

73
Q

How do lungs arrive in early embryo

A

Arise from lung bud, and endodermal structure adjacent to foregut - 4th week of development
Lung bud splits into two at end of 4th week, progressively branches through development

74
Q

How do gonads arise in early embryo

A

Form from mesoderm as bipotential structures - genital ridges

75
Q

In XY embryos

A

Presence of SRY gene on Y detects gonadal cells to become Sertoli cells, triggering development of testes, Leydig cell formation and testosterone production

76
Q

In XX embryos

A

Absence of SRY gene leads to gonads adopting a granulosa cell fate and ovary development, requires reinforcement by FOXL2

77
Q

Compaction

A

outer cells begin to flatten out
inner cells attach firmly to each other
tight junctions form between cells

78
Q

Gastrulation

A

forming layers -primitive groove
gives orientation

brs 1: development & aging domain (4 decks)

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