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BRS DEVELOPMENT AND AGEING > 1a Early Fetal Development > Flashcards

1a Early Fetal Development Flashcards

1
Q

What is the fertilization age?

A

The amount of time which has elapsed since fertilizaton

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2
Q

Why is fertilization age difficult to measure?

A

Time can elapse between intercourse and fertilization

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3
Q

In what instance can an exact fertilization age be established?

A

IVF

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4
Q

What is the gestational age?

A

The fertilization day + 14 days

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5
Q

How many stages of embryo development are there in the carnegie scale?

A

23

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6
Q

What does the Carnegie scale show?

A

Embryo features not time

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7
Q

Which time measurement can be used for comparing between species?

A

Carnegie

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8
Q

What window of time does the Carnegie scale show?

A

60 days

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9
Q

How many days post fertilization does the embryogenic stage last?

A

14 to 16 days

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10
Q

What is the name of the stage 16-50 days post fertilization?

A

Embryonic stage

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11
Q

What occurs in the embryogenic stage?

A

Established the early embryo from the fertilized oocyte, ad determination of two separate cell populations - he pluripotent cells and extra-embryonic cells

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12
Q

Which two types of cells are developed in the embryogenic stage?

A

Pluripotent embryonic cells and extra-embryonic

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13
Q

What happens in the embryonic stage of development?

A

Establishment of germ layers and differentiation of tissue types

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14
Q

When does the embryo to foetus transition occur?

A

During the first trimester

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15
Q

In what stage is the body plan established?

A

Embryonic stage

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16
Q

What happens to the organs in the fetal stage?

A

Migration of some organ systems to their final location

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17
Q

What is meant by fetal viability?

A

The ability of the foetus to survive outside the womb

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18
Q

What is the time period of the fetal stage?

A

50-270 days

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19
Q

Which stages of embryo-fetal development are in the first trimester?

A

Embryogenic and embryonic

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20
Q

What is the name given to the fertilized oocyte?

A

Zygote

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21
Q

When the embryo goes from 2 to 8 cells, what is this called?

A

Cleavage stage embryos

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22
Q

When is the embryo considered a morula?

A

When it has 16+ cells

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23
Q

What characterizes a blastocyst?

A

200 to 300 cells

And a fluid filled cavity

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24
Q

What is the embryo dependent on to get through the first few stages of development?

A

Maternal mRNAs and proteins

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25
Q

At what point do the embryos own genes get transcribed?

A

The 4 to 8 cell stage

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26
Q

What is the transcription of the embryonic genes called?

A

Zygotes genome activation

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27
Q

What happens in the zygote genome activation stage?

A

Increased protein synthesis

Organelle maturation

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28
Q

Which organelles mature during zygote genome activation?

A

Mitochondria and golgi

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29
Q

What is the maternal to zygote transition?

A

This is the transition between the embryo being dependent on mothers mRNAs and proteins, to transcribing its own genes

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30
Q

When are maternal mRNA and proteins synthesized and stored?

A

During oocyte develoment

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31
Q

What is compaction?

A

When the cells bind tight to each other and pull in

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32
Q

What starts the formation of the first two cell types?

A

Compaction

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33
Q

When does compaction occur?

A

Around the 8 cell stage or later

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34
Q

What happens when the outer cells become pressed against the zona pellucida?

A

They become pressed against the zona and consequently change shape from rounded to wedge shapes

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35
Q

How do the outer cells connect to each other?

A

Through desmosomes and tight junctions

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36
Q

What is the name given to the outer layer during blastocyst formation?

A

Trophectoderm

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37
Q

What type of cells does the inner cell mass contain?

A

Pluripotent stem cells

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38
Q

What are trophectoderm cells?

A

Extra-embryonic cells that contribute to the extra-embryonic structures like the placenta

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39
Q

What is the purpose of zona pellucida?

A

A hard shell protein to prevent polyspermy and protect the early embryo

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40
Q

What is the blastocoel?

A

A fluid filled cavity in the center of the blastocyst

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41
Q

How does the blastocoel form?

A

The trophoblast pumps Na+ ions into the cavity which water then follows with osmosis

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42
Q

What process occurs during day 5-6 in development?

A

Hatching - this is where the blastocyst breaks free from the zona pellucide

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43
Q

How does the blastocyst escape the zona pellucida?

A

Enzymatic digestion or cellular contractions - weakens the zona pellucida so much to allow the blastocyst to extrude itself out the shell

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44
Q

Where does the blastocyst implant itself following extrusion from the shell?

A

The uterine endometrium

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45
Q

What forms in the first stage of the separation of embryonic cell lineages?

A

Inner cell mass and the trophectoderm

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46
Q

What events happen from day 7 to 9?

A

Peri-implantation events

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47
Q

What does the trophectoderm layer separate into?

A

Syncytiotrophoblast and cytotrophoblast

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48
Q

What does the syncytiotrophoblast do?

A

It invades the uterine endometrium and starts to degrade the capillaries found there

Creates an interface between embryo and maternal blood supply

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49
Q

What does the inner cell mass divide into?

A

The epiblast and the hypoblast

50
Q

What is derived from the epiblast?

A

fetal tissues and organs

51
Q

What is derived from the hypoblast?

A

The yolk sak and other extra-embryonic structures

52
Q

What is the final stage before gastrulation and occurs on day 12?

A

The bilaminar embryonic disc formation

53
Q

How does the amniotic cavity form?

A

Some epiblast cells become separated from the epiblast

54
Q

What is the amnion?

A

An extra-embryonic membrane

55
Q

When is the embryo ready for gastrulation?

A

When the bilaminar disc of the epiblast and hypoblast sandwiched between the amniotic cavity forms

56
Q

What does the syncytiotrophoblast start to produce at the bilaminar disc stage?

A

hCG = human chorionic gondadotrophin

57
Q

What substance is detected during pregnancy tests?

A

The detection of the beta subunit of hCG in the maternal blood and urine

58
Q

What is gastrulation?

A

The process whereby the bilaminar embryonic disc undergoes reorganization to form a trilaminar disc, forming the three primary germ layers

59
Q

What are the three primary germ layers?

A

Ectoderm
Mesoderm
Endoderm

60
Q

What structure forms along the midline of the epiblast around day 15 post fertilisation?

A

Primitive Streak

61
Q

Towards which end of the embryo does the tail of the primitive streak originate from?

A

The caudal end

62
Q

What is formed when the primitive streak expands?

A

The Primitive pit

63
Q

What happens in the process of invagination?

A

Cells of the epiblast migrate towards the streak, detach and slip beneath in into the interior of the embryo

64
Q

What is the first germ layer to be formed?

A

The endoderm

65
Q

How does the endoderm form?

A

When epiblast cells invaginate and displace the hypoblast cells, forming a new layer called the endoderm

66
Q

How does the ectoderm form?

A

The remaining hypoblast cells which haven’t been replaced by epiblast cells then form the ectoderm

67
Q

How does the mesoderm form?

A

When some of the invaginated epiblast cells remain in the space between the endoderm and the ectoderm

68
Q

What happens when the mesoderm forms?

A

The epiblast cells no longer migrate towards the primitive streak

69
Q

When is gastrulation complete?

A

When all three layers have been formed

70
Q

What organ systems does the endoderm give rise to? GILLT

A

GILLT

GI Tract
Lungs
Liver
Trachea

71
Q

What organ systems does the mesoderm give rise to?

A

BMBG

Blood
Muscle
Bone
Gonads, Kidney and Adreal cortex

72
Q

What systems does the ectoderm give rise to?

A

CNS and neural crest
Skin epithelia
Tooth enamel

73
Q

What is the notochord?

A

A rod-like tube structure formed of cartilage-like cells that acts as a key organising center for neuralation and mesoderm development

74
Q

What does the notochord do?

A

Releases growth factor signals that are important for neuralation

75
Q

Where is the notochord relative to the neural plate?

A

The notochord lies below the nueral plate

76
Q

What affect does the notochord have on the neural plate?

A

it sends signals up from the notochord to move up through the embryo and direct the neural plate to invaginate forming the neural groove

77
Q

What is the neural groove?

A

A groove frmed through the formation of two neural ridges (neural folds) that run alongside the cranio-caudal axis

78
Q

What cells are found in the neural folds?

A

Neural creast cells

79
Q

What forms when the neural folds move together and eventually fuse?

A

Neural tube

80
Q

What overlays the neural tube?

A

Epidermis - which is ectoderm derived

81
Q

What are the two hallmarks of the neural crest cells?

A

They are plastic and highly migratory

82
Q

Around what day does the neural tube close at the head end?

A

23

83
Q

Around what day does the neural tube close around the tail end?

A

27

84
Q

What two conditions are common with the closure of the neural tube?

A

Anencephaly

Spina Bifida

85
Q

What causes anencephaly?

A

Failure of the neural tube to close at the head end

86
Q

What is spina bifida and what does it cause?

A

Neural tube defect caused when the neural tube is open at birth as the tail end has not closed

87
Q

What do cranial neural crest cells help to derive?

A

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

88
Q

What do cardial neural crest cells help to derive?

A

aortic arch, pulmonary artery septum, large arteries walls, musculoconnective tissue

89
Q

What do trunk neural crest cells help to derive?

A

Dorsal root ganglion, sympathetic ganglia, adrenal medulla, aortic arch clusters, melanocytes

90
Q

What do vagral and sacral neural crest cells help to derive?

A

Parasympathetic ganglia, and enteric nervous system ganglia

91
Q

What can defects of neural crest migration / specification lead to?

A

Pigmentation disorders, deafness, cardiac and facial defects, failure to innervate gut

92
Q

What is somitogenesis?

A

The formation of somites

93
Q

What are somites?

A

Blocks of mesoderm along the axis of the embryo

94
Q

How do somites form?

A

As development progresses, there is synchronized budding of the paraxial mesoderm from both sides at the same time, forming somites

95
Q

Where does somitogenesis commence?

A

At the head end of the embryo

96
Q

What is the rate of somite budding in humans?

A

1 pair every 90 minutes

97
Q

how many somite pairs do humans have?

A

44 pairs

98
Q

Where are the more defined somites found?

A

Towards the head end

99
Q

What two types of tissues do somites initially form?

A

Dermomyotome and sclerotome

100
Q

What is the sclerotome?

A

The vertabrae and rib cartilage

101
Q

What does the dermamyotome subdivide to form?

A

The dermatome and myotome

102
Q

What does the dermatome give rise to?

A

The dermis of the skin, fat, connective tissues of the neck and trunk

103
Q

What does the myotome give rise to?

A

Muscles of the embryo

104
Q

At what point does formation of the gut occur?

A

Day 16+

105
Q

What arises from the two types of folding in the embryo?

A

the primitive gut

106
Q

What are the two types of folding which occur to give rise to the primitive gut?

A

Ventral - where the head and tail ends curl together

Lateral - Where the two sides of the embryo roll

107
Q

What is the yolk sac derived from?

A

The hypoblast

108
Q

What is formed when part of the yolk sac is pinchd off?

A

The primitive gut

109
Q

What happens to the primitive gut after it is formed?

A

Patterened into the foregut, hindgut and midgut

110
Q

What does the foregut derive?

A

Esophagus, stomach, upper duodenum, liver, gall bladder, pancreas

111
Q

What does the midgut derive?

A

Lower duodenum, remainder of small intestine, ascending colon. first 2/3rds of the transverse colon

112
Q

What does the hindgut derive?

A

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

113
Q

When is the first fetal heart beat detected?

A

6 weeks gestational age

114
Q

How does the heart form?

A

Begins as a tube of mesoderm around day 19

115
Q

What do the lungs arise from?

A

The lung bud in the 4th week of development

116
Q

What do the gonads form from?

A

The mesoderm

117
Q

How does the embryo become a masculine embryo?

A

The presence of the SRY gene directs the gondal cells to become Sertoli cells, which triggers testes development, Leydig formation and testosterone production

118
Q

How do embryos become feminine?

A

Absence of SRY gene leads to gonadal cells adopting a granulosa cell fate and ovary development

119
Q

During compaction, how do the outer cells bind to each other?

A

Outer cells connect to each other through tight gap junctions and desmosomes

120
Q

What characterises a compacted morula?

A

The formation of two individual cell types - trophectoderm and inner cell mass

121
Q

What is the zona pellucida?

A

Hard protein shell inhibiting polyspermy and protects early embryo

BRS DEVELOPMENT AND AGEING (6 decks)

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