The Fate of the Mesoderm Flashcards Preview

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Flashcards in The Fate of the Mesoderm Deck (98):
1

What has happened by the end of the third week post fertilisation?

#NAME?

2

What ist he most plastic of the germ layers?

Mesoderm

3

What is meant by the mesoderm being the most plastic?

It gives rise to the biggest number of tissues

4

What is the notochord responsible for?

Releasing signals to surrounding ectoderm

5

What does the notochord undergo?

Neurulation

6

What forms the nervous system?

Notochord-driven induction of the ectoderm

7

What happens to the neural plate?

It folds up to form the tube which develops into the brain and spinal cord

8

What is the tube that develops into the brain and spinal cord called?

The neural tube

9

What is the formation of the neural tube key to?

Normal development of the CNS

10

What can result in problems with neural tube formation?

Spinabifida

11

When does neural tube formation occur?

23 days post fertilisation

12

What is the structure of the notochord during neurulation?

Solid rod of cells running in midline

13

What is the role of the notochord in neurulation?

Signalling

14

Where does the notochord run?

Between ectoderm and endoderm

15

What is the result of the notochord running between the ectoderm and endoderm?

Signals can reach the ectoderm

16

What does the notochord direct?

Conversion of overlying ectoderm to neuroectoderm

17

How does ectoderm become neuroectoderm?

Differentiation

18

What is neuroectoderm?

A type of tissue that goes on to give the CNS

19

What do notochord signals cause?

Overlying ectoderm to thicken

20

What does the thickening of overlying ectoderm lead to?

Slipper-shaped neural plate

21

How is the neural tube formed for the neural plate?

The edges elevate out of the plane of the disk, and curl towards each other

22

What causes the edges of the plate to rise up?

The cells grow faster at the edge

23

What gives rise to the majority of tissues?

Mesoderm

24

What is required for the mesoderm to give rise to the majority of tissue?

Rapid differentiation

25

What does mesoderm have lots of?

Discreet zones

26

What does each zone of the mesoderm have?

Separate tasks

27

What are the 4 types of mesoderm?

- Paraxial 
- Intermediate
- Somatic
- Splanchnic

28

Where is paraxial mesoderm found?

Either side of the axis

29

What is the somatic mesoderm to do with?

Body, and body structures, including skeletal muscle

30

What is the splanchnic mesoderm to do with?

Viscera and organs

31

What exists in additional to the 4 types of mesoderm?

Intraembyronic coalom

32

What is intraembryonic coalom?

Spaces inside the embryo that form a new cavity

33

How is paraxial mesoderm organised?

Into segments

34

When do the first pair of somites appear?

Day 20

35

Where do the first pair of somites appear?

In the occipital region

36

What is the advantage of the first pair of somites being a very predictable presentation?

It can be used to age foetus

37

Where do more somites appear following the first?

The craniocaudal sequence

38

How quickly do more somites appear?

3 pairs a day

39

How many somites pairs are eventually present?

42 to 44

40

What happens to some of the somite pairs?

They disappear

41

What is the ultimate number of somite pairs?

31

42

How do somites appear?

As regular block of mesoderm cells arranged around a small cavity

43

What is the appearance of somites followed by?

‘Organised degradation’

44

What happens in organised degradation?

The ventral wall of somite breaks down

45

What does organised degradation lead to?

The formation of sclerotome

46

What does organised degradation represent?

A loss of a clearly defined block structure, but still kept very ordered

47

What does further organisation of dorsal portion form?

The dorsal dermomyotome

48

How does the dermomyotome differ from the sclerotome?

It is even more organised

49

What does the dorsal dermomyotome contribute to?

Formation of skin and muscular formation

50

What does the myotome do?

Proliferates and migrates

51

What does the dermotome do?

Disperses

52

What does the myotome and dermatome remain affiliated to?

The parent somite

53

What are somite derivatives the beginning of?

Development of musculoskeletal system

54

What is the dermatome?

‘Skin section’

55

What is the myotome?

‘Muscle section’

56

What is the sclerotome?

‘Hard tissue’ section

57

What is the implication of segmentation?

- Organisation of mesoderm into somites give rise to repeating structures 
- Guides innervation

58

What repeating structures rise form somites?

- Vertebrae 
- Ribs 
- Intercostal muscles 
- Spinal cord segments

59

What is the epimere innervated by?

Dorsal branch of spinal nerve for that segment

60

What is the hypomere innervated by?

Vental branch

61

What is the significance of there being 31 somites?

Means there a 31 segments and therefore 31 pairs of spinal nerves

62

Developmentally, what is the dermatome?

The part of the somite that gives rise to the dermis

63

Developmentally, what is the myotome?

Gives rise to the muscle

64

Clinically, what is the dermatome?

A strip of skin supplied by a single spinal nerve

65

Clinically,

A muscle/group of muscles supplied by a single spinal nerve

66

Clinically, what is the dermatome and myotome the basis of?

Examination of musculoskeletal and nervous systems

67

What does mesoderm differentiate into?

- Notochord
- Paraxial 
- Intermediate 
- Somatic 
- Splanchnic

68

What does the paraxial mesoderm develop into?

- The axial skeleton
- Dermis 
- Muscles of A/L body wall 
- Some limb muscles

69

What does the axial skeleton consist of?

Vertebral column and ribs

70

What does the intermediate mesoderm develop into?

Urogenital system

71

What does the urogenital system consist of?

- Kidneys
- Ureters 
- Gonads

72

What does the somatic mesoderm develop into?

Connective tissue of limbs

73

What does the splanchnic mesoderm develop into?

- Smooth musculature 
- Connective tissue 
- Vasculature of gut

74

What will the buccopharyngeal membrane become?

The mouth

75

What will the cardiogenic area become?

The heart

76

Where on the embryonic disc is the cardiogenic zone of mesoderm?

Cranial end

77

What kind of folding does the embryonic disc undergo?

#NAME?

78

What is meant by cephalocaudal folding?

Folding at cranial (head) end and tail

79

What is cephalocaudal folding driven by?

Size of the neural tube

80

What is meant by lateral folding?

Folding of sides

81

What is lateral folding driven by?

Size of developing somite

82

What does folding create?

A pocket, with an opening into the umbilical cord

83

What is the result of of cephalocaudal folding?

A layer of mesoderm between ectoderm and endoderm, with future pericardial cavity next to it

84

What causes an expansion of the ectoderm?

The size of the neural tube

85

What does the expansion of the ectoderm do?

Pushes the head and tail under the layer of ectoderm, endoderm and mesoderm, leading to little pockets of yolk sac being pinched up into the embryonic body

86

What does the expansion of the amniotic sac downwards mean?

The whole embryo is wrapped in the amniotic sac, making sure whatever is facing outwards is ecroderm

87

What is the result of cephalocaudal folding on the heart?

It is now in the right place

88

What happens as the amniotic sac moves down?

- Get two ‘leaves’ at the lateral edges 
- Somites forming in paraxial mesoderm

89

What are the two ‘leaves’ at the lateral edges?

Somatic and splanchnic

90

What happens to the lateral edges of the disk?

They are forced down by growth of somites

91

What opens up between somatic and splanchnic layers?

Increasing space

92

What happens to the somatic and splanchnic ‘leaves’?

They develop downward, eventually meeting

93

What happens when the leaves meet?

They pinch off a bit of yolk sac

94

What is the result of the pinching off of yolk sac?

Results in cavity inside the embryo from the yolk sac

95

What does the cavity from the yolk sac allow for?

Development of systems

96

What does folding achieve?

- Draws together margins of disk 
- Creates ventral body wall
- Pulling amniotic membrane around disc, so embryo becomes suspended in it 
- Pulling connective stalk ventrally 
- Creates the primordium of the gut 
- Puts heart and primordium of diaphragm in right place
- Creates new cavity within embryo

97

Is the creation the ventral body wall an active or automatic process?

Active

98

What is the primordium of the gut created from?

The yolk sac