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BRS 1: Development & Aging Domain > 1.2: Early fetal development > Flashcards

1.2: Early fetal development Flashcards

(78 cards)

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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
Characteristics of the inner cell mass of a blastocyst
Pluripotent embryonic cells that contribute to final organism
26
Characteristics of the trophoectoderm
Extra-embryonic cells that contribute to the extraembryonic structures that support development
27
What happens to the blastocyst during hatching (day 5-6)
To implant, the blastocyst must escape zona pellucida Enzymatic digestion Cellular contractions
28
Separation of embryonic cell lineages I
Morula separates into : 1) inner cell mass (embryonic) 2) trophectoderm (extra-embryonic)
29
In peri-implantation (day 7-9) Trophoectoderm lineage separates further :
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
30
In peri-implantation (day 7-9) inner cell mass separates further into:
Epiblast: from which foetal tissues will be derived Hypoblast: which will form the yolk sac (extraembryonic structure)
31
Separation of embryonic cell lineages 2 : embryonic branch
Epiblast and Hypoblast
32
Separation of embryonic cell lineages 2: extra-embryonic branch
Cytotrophoblast, syncitiotrophoblast
33
What is the bi-laminar embryonic disc
(Two-layer) embryonic disc is the final stage before gastrulation
34
What happens during the bi-laminar embryonic disc formation (day 12-14)
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
What does a Syncitiotrophoblast secrete
hCG
36
Extra-embryonic cells differentiate further into
Syncitiotrophoblast Cytotrophoblast
37
Inner cell mass forms
Bilaminar disc
38
Formation of the primitive streak defines
Head-tail and left-right axes of embryo
39
Invagination of cells into primitive streak forms 3 germ layers:
Endoderm cells (first through the streak) Ectoderm remains on the upper (ventral) surface Mesoderm sandwiched between ends and ectoderm
40
What 5 organs form the endoderm Germ layer
GI tract Liver Pancreas Lung Thyroid
41
What 4 organs form the ectoderm germ layer
CNS Neutral crest Skin epithelia Tooth enamel
42
What 7 organs form the mesoderm germ layer
Blood Muscle Gonads Kidneys Adrenal cortex Bone Cartilage
43
What is the notochord
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
What occurs on days 13-17
formation of body plan: - notochord formation -neurulation -somitogenesis -formation of gut tube
45
What is neurulation
Formation of the neural tube and CNS
46
Process of neurulation and neural tube formation
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
At what day does the neural tube close at the head end
23 Precedes formation of brain structures
48
At what day does the neural tube close at the tail end
27
49
What two developmental defects does failure of neural tube closure cause
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
Neural crest cells characteristics
Ectoderm-derived, plastic and migrate extensively during development
51
4 neural crest cells
Cranial NC Cardiac NC Trunk NC Vagral and Sacral NC
52
Cranial NC give rise to
Cranial neurones, glia, lower jaw, middle ear bones, facial cartilage
53
Cardiac NC give rise to
Aortic arch, large arteries walls musculoconnective tissue
54
Trunk NC give rise to
Dorsal root ganglia, sympathetic ganglia, adrenal medulla, aortic nerve clusters, melanocytes
55
Vagral and Sacral NC give rise to
Parasympathetic ganglia and enteric nervous system ganglia
56
What do defects of neural crest migration lead to
Diverse birth defects; including pigmentation disorders, deafness, cardiac and facial defects, failure to inner age the gut
57
Somitogenesis is
Formation of somites -divide into two : Sclerotome - bones and rib cartilage Deermomyotome - dermatome (dermis of skin), myotome (muscles)
58
Somites arise from
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
How do somites form
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
Rate of budding in humans
1 pair / 80min, 44pairs
61
What two types of embryonic tissue do somites form
Sclerotome Dermomyotome
62
What does Sclerotome tissue form
Vertebrae Rib cartilage
63
What does dermomyotome tissue divide into
Dermatology Myotome
64
What does dermatome give rise to
Dermis of the skin, some fat and connective tissues of neck and trunk
65
What does the myotome tissue form
Muscles of embryo
66
When is the gut tube formed
Day 16+
67
What two types of folding in the embryo give rise to the primitive gut
Ventral folding - where the head and tail ends curl together Lateral folding - where two sides of the embryo roll
68
How is the primitive gut formed
Foldings in the gut pinch off part of the yolk sac Then patterned into foregut, midgut,and hindgut
69
Derivatives of the foregut
Esophagus, stomach, upper duodenum, liver, gallbladder, pancreas
70
Derivatives of the midgut
Lower duodenum, remainder of small intestine, ascending colon, first two-thirds of transverse colon
71
Derivatives of hindgut
Last third of transverse colon, descending colon, rectum and upper anal canal
72
How is the heart formed in an embryo
Begins as a tube of mesoderm around day 19, Beating and pumping blood commences day 22 Foetal heartbeat detectable from 6weeks gestational age
73
How do lungs arrive in early embryo
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
How do gonads arise in early embryo
Form from mesoderm as bipotential structures - genital ridges
75
In XY embryos
Presence of SRY gene on Y detects gonadal cells to become Sertoli cells, triggering development of testes, Leydig cell formation and testosterone production
76
In XX embryos
Absence of SRY gene leads to gonads adopting a granulosa cell fate and ovary development, requires reinforcement by FOXL2
77
Compaction
outer cells begin to flatten out inner cells attach firmly to each other tight junctions form between cells
78
Gastrulation
forming layers -primitive groove gives orientation

BRS 1: Development & Aging Domain (4 decks)

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