The Pre-Embryonic Period Flashcards Preview

Z OLD Tissues of the Body > The Pre-Embryonic Period > Flashcards

Flashcards in The Pre-Embryonic Period Deck (129):
1

How does once cell become a multicellular body?

Growth, Morphogenesis, Differentiation

2

What does morphogenesis involve?

Creating lots of cells in the right place at the right time

3

What is the result of morphogenesis?

The development of form and structure

4

Why is differentiation needed?

For specialisation for function

5

What does differentiation allow?

Certain groups of cells to specialise for a common function

6

What are the 3 stages from fertilisation to birth?

- Pre-embryonic 
- Embryonic 
- Fetal

7

When is the pre-embryonic period?

Weeks 1-2

8

When is the embryonic period?

Weeks 3-8

9

Why is the embryonic period such a critical period?

All structures and systems of the body are made

10

When is the foetal period?

Weeks 9-38

11

What happens in the foetal period?

The focus is on growth and physical maturation of systems

12

When are pregnancy weeks calculated from?

LMP, i.e. conception weeks +2

13

How long is a term pregnancy?

40 weeks

14

What happens in the pre-embryonic period?



  • Cleavage

  • Compaction

  • Implantation begins


15

What is happening in cleavage?

Mitotic division

16

Why is cleavage significant?

Because have established a new individual

17

What is formed from cleavage?

Morula

18

What is the morula?

A clump of cells

19

What happens in compaction?

The formation of a blastocyst

20

What is implantation?

The process by which the blastocyst makes contact with the endometrium of the uterus

21

What does implantation begin?

The establishment of the pregnancy

22

Where is the oocyte released from?

The ovary

23

What happens to the oocyte once it’s been released?

It travels along the Fallopian tubes

24

Where is the oocyte fertilised?

Ampulla

25

What fertilises the oocyte?

Sperm

26

What is the ampulla of the fallopian tubes?

The fan bit just above the ovary

27

What is the fertilised oocyte called?

The zygote

28

Where is the ideal site for implantation?

The posterior uterine wall

29

What does the zygote need to do before it can implant?

Continue to travel alone the fallopian tube to get where it needs to be to establish the pregnancy

30

How long is an oocyte viable for?

1 day

31

How long is sperm viable for?

3 days

32

What happens immediately after fertilisation?

Sperm is excluded due to a complex chemical reaction

33

When does cleavage begin?

30 hours after fertilisation

34

What does cleavage result in?

2 blastomeres of equal size

35

What is the zona pellucida?

A glycoprotein ‘shell’

36

What is the result of the presence of the zona pellucida?

The blastomeres are about half the size of the oocyte, as the cell prevents it from expanding

37

What has happened by day 3 post fertilisation?

The morula has formed

38

What feature does each cell have at the morula formation stage?

They are totipotent

39

What is meant by the cells being totipotent?

They have the capacity to become any cell type

40

What happens in assisted reproductive techniques?

The oocytes are fertilised in vitro, and allowed to divide to the 4- or 8- cell stage. The morula is then transferred into the uterus

41

What is PGD?

When a cell is removed from the morula and tested for serious heritable conditions prior to the transfer of the embryo into the mother

42

What is compaction?

Formation of the first cavity

43

What is the first cavity formed?

The blastocyst

44

How is the blastocyst formed?

The cells of the morula are secreting tiny amounts of tissue fluid. Together, collect a sufficient amount that it collects, and one clump of cells pushes to one side, giving a space

45

What does the formation of the blastocyst give?

2 groups of cells

46

What is the inner group of cells called?

Embryoblast

47

What is the outer group of cels called?

Trophoblast

48

What happens to the inner group of cells of the blastocyst?

It goes on to give the embryo

49

What happens to the outer cells of the blastocyst?

They go on to produce the supporting tissues

50

What tissues support the embryo during pregnancy?

#NAME?

51

Why can cells produced by the first divisions after fertilisation become inner or outer cell mass?

Because they are all totipotent, so they have the capacity to become any cell type

52

What are cells after compaction?

Pluripotent

53

What is meant by pluripotent?

Cells have the capacity to become one of many cell types

54

What potential are pluripotent cells said to have?

Multi-lineage potential

55

What do the inner cell mass cells have the capacity to do?

Become any cell in the human body

56

What happens at day 5 post fertilisation?

Hatching

57

What is meant by hatching?

The blastocyst hatches from the zona pellucida

58

Why must the blastocyst hatch?

Up until now, the zona pellucida remains in tact, meaning it becomes quite restrictive, so we must get rid of it

59

What is the result of hatching?

The blastocyst is no longer constrained, and so is free to enlarge

60

What can the blastocyst do once it’s hatched?

Interact with the uterine surface to implant

61

When does implantation begin?

Day 6-7

62

How long does implantation run for?

A very long time- not complete until the end of the first trimester (~3 months)

63

What is the conceptus?

All the products of conception- the embryo and all its tissues

64

How many cells does the conceptus have at implantation?

107

65

How many cells of the conceptus at implantation will make the embryo?

8

66

How many cells of the conceptus at implantation will contribute to the development of foetal membrane?

99

67

Why is it important that foetal membranes are established?

It ensures that we can establish and maintain the pregnancy

68

Where does the conceptus implant?

Onto the uterine epithelium, which lines the uterine stroma

69

What development has priority at the very earliest stages?

Placenta

70

What important process occurs in week 2?

Differentiation

71

Where do two distinct cell layers emerge from?

The outer cell mass

72

What distinct cell layers emerge from the outer cell mass?

- Syncytiotrophoblast 
- Cytotrophoblast

73

What is the syncytiotrophoblast good for?

Transporting

74

What is purpose of the cytotrophoblast?

Allows the syncytiotrophoblast grow and increase in SA

75

What does the inner cell mass develop into?

A bilaminar disc

76

What does the bilaminar disc consist of?

#NAME?

77

In summary, what has happened by the end of the second week?

#NAME?

78

What are the two cavities of the embryo by the end of week two?

#NAME?

79

What is the name of the sac supporting the embryo?

The chorionic cavity

80

What is the amniotic sac formed from?

Spaces within the epiblast

81

What can implantation cause?

A small amount of bleeding

82

Why might implantation cause a small amount of bleeding?

Because it’s in invasive process

83

Why is implantation an invasive process?

The conceptus has to break through the endothelial lining

84

What must happen once the conceptus has broken through the endothelial lining?

The lining must be repaired

85

How is the endothelial lining repaired?

Using a fibrin plug

86

What is meant my implantation being interstitial?

The two tissues have a very close relationship- they are embedded

87

Where does the conceptus implant?

Within the uterine stroma

88

Why does the conceptus implant within the uterine stroma?

Because then it has access to all glands

89

What does implantation establish?

Maternal blood flow within the placenta- the basic structural unit of materno-fetal exchange

90

What change does implantation mark?

The support for embryo changes from histiotrophic to haemotrophic

91

What is meant by histiotrophic?

Support for tissues based on simple diffusion

92

Why must support for the embryo change from histiotrophic?

Because staying with this would drastically limit the size that it could grow

93

What is meant by haemotrophic?

Relying on support from maternal circulatory system

94

Why does the basic structural unit for materno-fetal exchange have to be within the placenta?

To allow for gas exchange, absorption of nutrients and removal of waste products from the foetus

95

Give 4 conditions linked to implantation defects

- Interuterine growth restriction (IUGR)
- Pre-eclampsaia 
- Ectopic pregnancy
- Placenta praevia

96

What kind of defect causes ectopic pregnancy and placenta praevia?

When the conceptus implants at the wrong site

97

Where does the conceptus implant in an ectopic pregnancy?

At a site other than the uterine body, most commonly the Fallopian tubes

98

What are the two types of ectopic pregnancy?

#NAME?

99

What is the problem with ectopic pregnancy?

It can very quickly become a life threatening emergency, as it can cause haemorrhage

100

Where does the conceptus implant in placenta praevia?

In the lower uterine segment

101

What is the problem with placenta praevia?

It can cause haemorrhage in pregnancy

102

Why can placenta praevia cause haemorrhage?

If implantation occurs very near the point of exit, the placenta can grow across, causing the mother to bleed out

103

What does placenta praevia necessitate?

C-section delivery

104

What happens on day 9 post fertilisation?

- Embryonic pole develops 
- Abembryonic pole develops

105

What causes the development of the embryonic pole?

The rapid development of the syncytiotrophoblast

106

What happens once the abembryonic pole has been formed?

The primitive yolk sac is formed

107

What is the significance of the formation of the primitive yolk sac?

You then have an embryo with two cavities

108

What is the yolk sac membrane in contact with?

The cytotrophoblast layer

109

What are present in the syncytiotrophoblast?

Lacunae

110

What are lacunae?

Spaces opening up

111

What is the purpose of lacunae?

They allow for rapid increasing SA

112

What happens on day 11 post fertilisation?

Primitive yolk sac membrane pushed away from the cytotrophoblast layer

113

What pushes the cytotrophoblast layer away from the primitive yolk sac membrane?

An acellular extraembryonic reticulum

114

What later happens to the acellular extraembryonic reticulum?

Its converted into extraembryonic mesoderm by cellular migration

115

What happens on day 12 post fertilisation?

Maternal sinusoids are invaded by syncytiotrophoblast

116

What happens once the maternal sinusoids have been invaded by the syncytiotrophoblast?

The lacunae become continuous with the sinusoids

117

What does maternal sinusoids being invaded by syncytiotrophoblast begin?

Uteroplacental circulation

118

What is the uterine stroma preparing for when the maternal sinusoids are invaded by syncytiotrophoblast?

Support of the embryo

119

What happens day 13 post fertilisation?

Formation of the secondary yolk sac

120

Where does the secondary yolk sac come from?

Pinches off from the primitive yolk sac

121

What happens day 14 post fertilisation?

Spaces within the extra-embryonic mesoderm merge

122

What is formed when spaces within the extra-embryonic mesoderm merge?

The chorionic cavity

123

What suspends the embryo and its cavities?

The connecting stalk

124

What is the connective stalk made up of?

A column of mesoderm and future umbilical cord

125

What can bleeding be confused for at day 14?

Menstrual bleeding

126

What % of zygotes are lost within the first 2-3 weeks?

~50%

127

What % of diagnosed pregnancies miscarry?

15%

128

What % of women suffer from recurrent miscarriages?

1%

129

What is meant by recurrent miscarriages?

Miscarriages in 3 consecutive pregnancies