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DEVELOPMENT AND AGEING - BRS > Early Fetal Development > Flashcards

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

0-60 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? - 2

A

a) Established the early embryo from the fertilized oocyte
b) 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? - 2

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? - 2

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 from the morula?

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? - 2

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

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50
Q

What is derived from the epiblast?

A

fetal tissues and organs

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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 neurulation

75
Q

Where is the notochord relative to the neural plate?

A

The notochord lies below the neural plate

76
Q

What effect 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 formed 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 crest 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 => absence of skull and brain

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 => lower spine impacted

87
Q

What do cranial neural crest cells help to derive? - 5

A

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

88
Q

What do cardial neural crest cells help to derive? - 4

A

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

89
Q

What do trunk neural crest cells help to derive? - 5

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? - 2

A

Parasympathetic ganglia, and enteric nervous system ganglia

91
Q

What can defects of neural crest migration / specification lead to? -4

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, that give rise to important structures associated with the vertebrate body plan

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
Lateral

107
Q

What is the yolk sac derived from?

A

The hypoblast

108
Q

What is formed when part of the yolk sac is pinched 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? - 6

A

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

111
Q

What does the midgut derive? - 4

A

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

112
Q

What does the hindgut derive? - 4

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, adjacent to the foregut

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 SRY gene => directs gondal cells to become Sertoli cells => 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

122
Q

what is neurulation

A

a process in which the neural plate bends up and later fuses to form the hollow tube that will eventually differentiate into the brain and the spinal cord of the central nervous system

123
Q

what is ventral folding

A

where the head and tail ends curl together

124
Q

what is lateral folding

A

Where the two sides of the embryo roll

125
Q

what is the fertilisation age also known as?

A

conceptual age

126
Q

what does the trophoblast divide into? - 2

A

cytotrophoblast and syncitiotrophoblast

DEVELOPMENT AND AGEING - BRS (3 decks)

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