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BRS Year 2 > Early Embryo Development > Flashcards

Early Embryo Development Flashcards

1
Q

When is fertilisation age measured from?

A

From the time of fertilisation, assumed to be more than one day from the last ovulation

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2
Q

What other name is fertilisation date known as?

A

Conceptualisation date

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3
Q

How practical is fertilisation date?

A

Not very, its also difficult to know the time exactly of ovulation so its not used very commonly

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4
Q

When is gestational age measured from?

A

From the time of the beginning of the last period

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5
Q

How is gestational age determined?

A

Fertilisation date + 14 days if known

Early obstetric ultrasound

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6
Q

How practical is gestational date?

A

More practical, it is used often clinically

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7
Q

What is carnegie age?

A

23 stages of embryo development based on embryo features not time

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8
Q

What window does carnegie age cover?

A

0-60 days fertilisation age (in humans)

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9
Q

What are the 3 major stages of time in embryo foetal development?

A

Embryogenic stage
Embryonic stage
Foetal stage

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10
Q

How many days post fertilisation is the embryogenic stage?

A

14-16 days

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11
Q

How many days post fertilisation is the embryonic stage?

A

16- 50 days

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12
Q

How many days post fertilisation is the foetal stage?

A

50-270 days or 8-38 weeks

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13
Q

What happens in the embryogenic stage?

A

Establishment of the early embryo from the fertilised oocyte

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14
Q

What are the 2 populations of cells in the embryogenic stage and what do they do?

A 
Pluripotent embryonic cells (contribute to fetus)
Extraembryonic cells (contribute to the support structures eg placenta)
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15
Q

What do pluripotent embryonic cells contribute to?

A

The foetus

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16
Q

What so extraembryonic cells contribute to?

A

Support structures eg placenta

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17
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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18
Q

What is present when the foetal stage is reached?

A

Major organ systems

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19
Q

What stages does the first trimester include?

A

Embryogenic and embryonic

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20
Q

What stages does the second trimester include?

A

Foetal stage

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21
Q

When does the transition from embryo to foetus occur?

A

At the end of the first trimester

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22
Q

How many cells is an ovulate oocyte?

A

1

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23
Q

How many cells is a zygote?

A

1

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24
Q

How many cells is a cleavage stage embryo

A

2-8

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25
Q

How many cells is a morula?

A

16

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26
Q

How many cells is a blastocyst?

A

200-300

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27
Q

When is the zona pellucida present?

A

From ovulated oocyte until blastocyst

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28
Q

Does the embryo transcribe its own genes?

A

No, it is dependant on materal mRNAs and proteins to get through the first few divisions until it has 4/8 cells. Failure in the mother to synthesise and store these mRNAs during oogenesis can impair development of the embryo

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29
Q

What happens at the maternal to zygotic transition?

A

Transcription of embryonic genes begins due to zygotic genome activation
Increased protein synthesis
Organelles mature eg mitochondria, Golgi

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30
Q

At what cell stage does compaction occur?

A

When the zygote is around 8 cells

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31
Q

Describe the process of compaction

A

Outer cells become pressed against zona pellucida
Change from spherical to wedge-shaped
Outer cells connect to each other through tight gap junctions and desmosomes
Forms barrier to diffusion between inner and outer embryo
Outer cells become polarized

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32
Q

What are the cell types in the blastocyst? Describe them

A

Inner cell mass are pluripotent embryonic cells that will contribute to the final organism
Trophoectoderm are extra-embryonic cells that contribute to the extraembryonic structures that support development

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33
Q

What is the zona pellucida?

A

Hard protein shell inhibiting polyspermy and protects early embryo

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34
Q

What is the blastoceal?

A

Fluid-filled cavity formed osmotically by trophoblast pumping Na+ ions into cavity and then water following osmotically

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35
Q

What is hatching?

A

Degredation and weakening of the zona pellucida to allow the blastocyst to escape it

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36
Q

Why is hatching required?

A

To allow the blastocyst to implant into the uterus

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37
Q

How is hatching achieved?

A

Enzymatic digestion of the zona pellucida and cellular contractions to allow the blastocyst to escape the seal

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38
Q

What does the morula split into? Describe what each component contributes to

A

Inner cell mass which contributes to embryonic cells

Trophectoderm which contributes to extra embryonic cells

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39
Q

What is formed when trophoblast cells fuse

A

Syncitiotrophoblast

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40
Q

What ability does the syncitiotrophoblast have?

A

It can invade and destroy local maternal cells in the endometrium, the destruction of capillaries allows the embryo to be bathed in blood which is an important interface

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41
Q

What individual cells are a source of syncitiotrophoblast cells?

A

Cytotrophoblasts

42
Q

What does the inner cell mass separate into and what are the roles of these cells?

A

Epiblast from which the foetal tissues will be derived

Hypoblast which will form the yolk sac

43
Q

What is the yolk sac needed for

A

Haematopoiesis and gut development

44
Q

What does the trophoblast give rise to?

A

Cytotrophoblast

Syncitiotrophoblast

45
Q

When does bi laminar embryonic disc formation occur?

A

After day 12

46
Q

What is the final stage before gastrulation?

A

Bi laminar embryonic disc formation

47
Q

Where particularly do changes occur in bi laminar embryonic disc formation?

A

Epiblast and hypoblast

48
Q

What are the 2 layers of a bi laminar embryonic disc made of?

A

Epiblast and hypoblast

49
Q

What secretes hCG and when?

A

Syncitiotrophoblast after 12 days

50
Q

What does the epiblast give rise to?

A

The epiblast and the amnion

51
Q

What is the role of the amnion cells?

A

They contribute to the extra-embryonic membranes

52
Q

Define gastrulation

A

The process by which the bilaminar embryonic disc undergoes reorganisation to form a trilaminar disc

53
Q

When does gastrulation occur?

A

3rd week- day 15

54
Q

Describe the primitive streak and what it defines

A

A thickened structure that forms along a midline of the epiblast near the caudal end of the bilaminar embryonic disc
Defines the cranial end (towards the head) and caudal end (towards the feet) as well as the left and right sides of the embryo

55
Q

When does the primitive streak form?

A

15 days after fertilisation

56
Q

What is the primitive pit?

A

An expansion of the primitive streak at the cranial end creates a primitive node that contains a circular depression called the primitive pit

57
Q

What is formed by the continuation of the primitive pit?

A

Primitive groove

58
Q

What is invagination in relation to gastrulation?

A

Cells migrate towards primitive streak, detach from the epiblast and migrate into the internal part of the embryo

59
Q

What cells form the endoderm?

A

The first cells to carry out invagination and invade the hypoblast

60
Q

At what day has much of the hypoblast been invaded and replaced?

A

Day 16

61
Q

What cells is the mesoderm formed by?

A

The remaining cells in the space between the ectoderm and definitive endoderm

62
Q

What is the definitive endoderm?

A

Layer that the hypoblast cells are completely replaced by

63
Q

What cells is the ectoderm formed by?

A

Remaining cells of the epiblast

64
Q

What 3 layers are formed in gastrulation (from exterior to interior)?

A

Ectoderm
Mesoderm
Endoderm

65
Q

When do epiblast cells stop migrating to the primitive streak?

A

After the mesoderm and ectoderm are formed

66
Q

What does the epiblast give rise to?

A

Ectoderm
Mesoderm
Endoderm

67
Q

What does the endoderm give rise to?

A 
GI tract
Liver
Pancreas
Lung
Thyroid
68
Q

What does the ectoderm give rise to?

A

CNS and neural crest
Skin epithelia
Tooth enamel

69
Q

What does the mesoderm give rise to?

A 
Blood (endothelial cells, RBCs, WBCs)
Muscle (smooth, skeletal and cardiac)
Gonads
Kidneys
Adrenal cortex
Bone
Cartilage
70
Q

What day does notochord formation occur?

A

Day 13

71
Q

What is the role of the notochord?

A

Acts as a key organizing center for neurulation and mesoderm development

72
Q

What type of cells form notochord?

A

Cartilage like cells

73
Q

What is neurulation?

A

Formation of the neural tube and CNS

74
Q

Describe the process of neurulation briefly

A

Notochord signals direct the neural plate ectoderm to invaginate forming a neural groove
This creates two ridges
Neural folds move together over neural groove and ultimately fuse, forming a hollow tube

75
Q

What is the key signalling structure in neurulation?

A

The notochord

76
Q

Which end of the neural tube closes first?

A

The head end closes first then the tail end

77
Q

What can happen once the ends of the neural tubes close

A

The brain structures can be formed

78
Q

What are the main disorders that occur if the neural tubes don’t close

A

Anencephaly

Spina bifida

79
Q

What is anencephaly?

A

A disorder that occurs when the neural tube doesn’t close at the head end

80
Q

What is spina bifida?

A

A disorder that occurs when the neural tube doesn’t close at the tail end, it has varying severity

81
Q

Where are neural crest derived from?

A

From the ectoderm

82
Q

What are some characteristics of neural crest cells?

A

They are plastic and migrate extensively during development

83
Q

What are some defects that arise due to neural crest migration?

A

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

84
Q

What do somites arise from and how?

A

From paired blocks of paraxial mesoderm flanking the neural tube and notochord
Blocks of paraxial mesoderm condense and bud off in somite pairs

85
Q

At what end does somitogenesis occur?

A

Head end

86
Q

In humans what rate does budding of somites occur?

A

1 pair every 90 mins

87
Q

In humans how many pairs of somites are there?

A

44 pairs

88
Q

What 2 types of tissue do somites form?

A

Sclerotome

Dermomyotome

89
Q

What does the sclerotome give rise to?

A

Vertebrae and rib cage

90
Q

What does the dermomyotome split into?

A

Dermatome and myotome

91
Q

What does the dermatome give rise to?

A

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

92
Q

What does the myotome give rise to?

A

Muscles of the embryo

93
Q

What 2 types of folding allow the formation of the primitive gut?

A

Ventral folding: where the head and tail ends curl together

Lateral folding: where the two sides of the embryo roll

94
Q

What are the 3 parts of the gut which develop from the primitive gut?

A

Foregut
Midgut
Hindgut

95
Q

When is foetal heartbeat detectable?

A

Around 6 weeks

96
Q

What does the heart arise from?

A

Tube of mesoderm

97
Q

What gene is specific to the Y chromosome?

A

SRY gene

98
Q

What does the SRY gene do?

A

Directs gonadal cells to become sertoli cells, triggering testis development, leydig cell formation and testosterone production

99
Q

What does absence of the SRY gene do?

A

Leads to gonadal cells adopting a granulosa cell fate and ovary development

100
Q

What reinforcing gene is needed for ovary development etc?

A

FOXL2

BRS Year 2 (110 decks)

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