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z:2017 - Biosci107 1/2 > Gastrulation and Morphogenesis > Flashcards

Gastrulation and Morphogenesis Flashcards

1
Q

What is gastrulation?

A

The process which the bilaminar embryo is transformed into one that has 3 germ layers

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2
Q

What are the three germ layers that form in gastrulation?

A

Ectoderm, mesoderm, endoderm

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3
Q

What do the germ layers form?

A

All the tissue of the baby

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4
Q

What tissue types form from ectoderm?

A

The epithelium of the skin and nervous system

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5
Q

What tissue types form from mesoderm?

A

Bones, muscles and mesenteries (tissue that covers internal organs and attaches organs to cavity walls)

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6
Q

What tissue types form from endoderm?

A

Lining of the gut and large glands such as liver and pancreas

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7
Q

What is the first sign of gastrulation?

A

The formation of a primitive streak

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8
Q

What does the primitive streak define in the embryo?

A

Both the midline and caudal end of the embryo

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9
Q

What is the purpose of forming a primitive streak?

A

It creates symmetry in the organism

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10
Q

How does the primitive streak form?

A

When the cells in the epiblast start migrating downward from the midline at the tail end of the epiblast then down towards the hypoblast. More cells join movement towards midline further from the tail end and the primitive streak elongates rostrally (towards the head)

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11
Q

As the embryo develops, what happens to the primitive streak? Why?

A

It shortens as the tip of the primitive streak moves back towards the tail Fewer cells are actively migrating

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12
Q

What kind of structure is the primitive streak? What makes it visible?

A

It isn’t a structure Cells migrating from epiblast towards hypoblasts makes it visible

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13
Q

As the primitive streak grows and shrinks, what impact does this have on the cells?

A

The cells that are closer to the head undergo gastrulation later on and for a shorter period of time than the cells at the tail end

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14
Q

What is the end of the gastrulation where new cells are migrating downwards called?

A

The node

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15
Q

What do the epiblast cells need to do to migrate?

A

They need to lose all their intercellular connections and form a shape which can allow them to migrate

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16
Q

What do the epiblast cells do as they’re about to migrate?

A

They detach from the epithelium of the amion cells and form a ball shape

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17
Q

What do the epiblasts do as they are migrating?

A

They push down into the hypoblast layer and displace the hypoblast layer

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18
Q

Why is the hypoblast displaced by the epiblast?

A

In order to form the inner lining of the yolk sac

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19
Q

What do the epiblasts that displace the hypoblasts give rise to?

A

The endoderm

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20
Q

Once the epiblasts have migrated into the hypoblast layer, where do the epiblast cells continue to migrate to?

A

They migrate into the space between the epiblasts and endoderm/hypoblast

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21
Q

What germ layer do the epiblasts between the original top layers of epiblast and the endoderm give rise to?

A

The mesoderm

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22
Q

How is the mesoderm arranged as it develops?

A

Starts off as loosely packed then comes together forming well defined structures

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23
Q

What happens to the remaining epiblast on the top layer once gastrulation has finished?

A

It turns into ectoderm

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24
Q

Because the node moves from the tail to head end, how is gastrulation different in the head?

A

It happens later than in the tail

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25
Q

What does the gastrulation process create?

A

A three layered embryo

26
Q

What are mesenchyme?

A

They are the mesoderm in a loosely packed state

27
Q

What is a mesenchymal transformation?

A

When the epiblasts lose their epithelial morphology and form loosely packed mesenchyme cells

28
Q

What structures do the mesenchyme form once it condenses? Where are they in the mesoderm layer?

A

Form: notochord, middle Somites, one on each side of the notochord Intermediate mesoderm, a rod of mesoderm tissue on each side of the somites Lateral plate mesoderm, folded over plates on each side of the intermediate mesoderm

29
Q

How do the mesoderm paths during gastrulation impact the tissue development?

A

The direction the cells take determines what kind of tissue is formed

30
Q

What kind of tissue is formed from mesoderm cells that go forward, i.e. the first stream of cells during gastrulation (towards the head)? What main structure does this form?

A

Axial mesoderm Notochord

31
Q

What kind of tissue is formed from the mesoderm cells that go out in the second stream during gastrulation (e.g. to the side a little bit)? What structure does this form?

A

Medial paraxial mesoderm Forms the medial side of the somites (part of the somite closest to the notochord)

32
Q

What kind of tissue is formed from the mesoderm cells that go out in the third stream during gastrulation (further out from the second team)? What structure does this form?

A

Lateral paraxial mesoderm Forms the lateral side of the somite (part of the somite furtherest from the notochord)

33
Q

What kind of tissue is formed from the mesoderm cells that go out in the fourth stream during gastrulation (go backwards from the node)?

A

Forms the intermediate and lateral plate mesoderm

34
Q

What other process is occurring at the same time as gastrulation?

A

Convergence extension

35
Q

What happens during convergence extension?

A

The embryo becomes longer between the head and tail and thinner on the sides, becoming oblong

36
Q

How is the head determined on the embryo?

A

It is always opposite from the starting position of the primitive streak

37
Q

How are the different cells within an embryo told what kind and how to form the tissues required of the baby?

A

Differentiation signals (tissue type, e.g. muscle, bone…) Global signals (tissue specialisation, e.g. pectoral muscle, compact bone…)

38
Q

What system is used to determine the body plan of the embryo?

A

Tail organiser and head organiser

39
Q

What forms the tail organiser?

A

The node on the primitive streak

40
Q

What forms the head organiser? Hows is this component formed?

A

The anterior visceral endoderm which is when the hypoblast gets pushed to the head end as the primitive streak moves along

41
Q

What do organisers produce?

A

They secrete morphogens

42
Q

What do morphogens do? How can it impact cell function?

A

Determines what the cell does, stimulates expression of hox genes Concentration and timing of cells exposed to it

43
Q

How does cells recognise if they are at the tail or head end of the embryo with morphogens? What do they do with this information?

A

Tail and head organisers produce tail and head morphogens, the amount of morphogens of each kind determines how close the cell is to the head/tail (e.g. if receiving lots of tail but not many head morphogens then it is closer to the tail end etc.) With this positional info they cell can then determine if it should produce more or less head/tail structures

44
Q

What are the two kinds of actions morphogens can have? What do these actions do?

A

Agonist - stimulates something to happen Antagonists - prevents something from happen

45
Q

Generally, what kind of actions do head morphogens do?

A

They are generally antagonist blocking the functions of tail organisers

46
Q

What are functions of hox genes?

A

They are the global signals that indicate what genes are expressed to create specific body parts

47
Q

What tissues does the hox gene influence?

A

It affects all three embryonic tissues: endoderm, mesoderm ectoderm

48
Q

Where are limb buds generated during embryonic development? What are limb buds?

A

At the borders of the hox genes

They are the points on an orgnaism where the limbs will grow from

49
Q

What is transverse folding?

A

The process which the three embryonic layers fold over through the MIDDLE AXIS RUNNING FROM THE HEAD TO THE TAIL to form the structures for the intestines (inside), skin (outside) and muscle (middle)

50
Q

Describe the structure of the embryo before transverse folding

A
51
Q

What happens to the amniotic cavity as the embryo undergoes transverse folding?

A

It folds over the embyro until it covers the entire embryo forming a amniotic sac

52
Q

When does the endoerm close up?

A

It never does, there is always a slight gap where there is contact with the yolk sac

53
Q

What is longitudinal bending?

A

The process where the head and the tail end curve into a C shape

54
Q

What tissue is folding over to form the C shape during longitudinal bending?

A

The neural tube

55
Q

What happens to the endoderm and ectoderm as the embryo undergoes longitudinal bending?

A

The endoderm folds underneath the neural tube and the ectoderm folds over the top of the neural tube

56
Q

What axis does longitudinal bending occur?

A

The rostro-caudal axis

57
Q

What happens as the head and tail move downwards during longitudinal bending? What does this form?

A

The endoderm moves toward the middle forming a tube with blind ends that will eventually become the gut

58
Q

What happens as the head and tail move downwards during transverse folding?

A

The lateral edges of the trilaminar embryo (it has 3 layers, ectoderm, mesoderm and endoderm FYI) move downwards and meet along the midline so the embryo is transformed into a tube (eg folds over into the tube)

59
Q

What is the end result of longitudinal and transverse folding? What is the exception to what has formed?

A

Embryo becomes a closed tube

except for the small opening that connects the inside of the gut to the yolk sac

60
Q

Describe the struture of an embryo cross-section after transverse folding and longitudinal bending

A
61
Q

How long after fertilisation does the embryo begin to resemble the structure of a typical vertebrate?

A

One month

62
Q

What does the ectoderm develop into?

A

the epithelium of the skin

z:2017 - Biosci107 1/2 (18 decks)

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