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PRIS (CLB) > Developmental Biology > Flashcards

Developmental Biology Flashcards

Intro - Embryology

1
Q

What is the definition of developmental biology?

A

The study of the process by which animals grow and develop (the transient stages between egg and birth)

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2
Q

Why do we use model organisms (3 reasons)?

A

1) They are easy to breed
2) They are easy to maintain in the lab
3) They share some human similarities

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3
Q

Why are invertebrates used as models (4 reasons)?

A

1) Easy to manage in large numbers
2) Short life span
3) Easily mutated
4) Genome sequenced

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4
Q

Why are anamniotes (fish & frogs) used as models (5 reasons)?

A

1) Embryos develop externally to the mother
2) Large eggs
3) Transparent - good for observing anatomical development
4) Easy to mutate
5) Sequenced genome

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5
Q

Why are amniotes (mouse & chicken) used as models (4 reasons)?

A

1) Some develop externally to mother
2) Can do mammalian transgenics (insert foreign genes)
3) Closer genome to humans
4) Sequenced genomes

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6
Q

What are the 5 key stages of fertilisation before gastrulation?

A
  1. Fertilisation
  2. Cleavage Stage
  3. The Morula
  4. Blastocyte Stage
  5. Blastocyte hatches
  6. Implantation
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7
Q

In fertilisation, what are the primordial germ cells?

A

The sperm and egg cells.

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8
Q

How do primordial germ cells become regular germ cells?

A

Primordial germ cells (2n) undergo meiosis in order to form haploid (n) cells.

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9
Q

How and when is a zygote formed?

A

Zygote is formed during fertilisation when the sperm enters the oocyte.

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10
Q

At fertilisation, how is polyspermy prevented?

A

The zona pellicida ensures the oocyte becomes impenetrable after fertilisation,

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11
Q

What happens once the zona pellucida becomes impenetrable after fertilisation?

A

Cells begin dividing via mitosis

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12
Q

After fertilisation, cleavage occurs. What happens during cleavage?

A

During cleavage:
- Cells divide and become smaller
- These cells are now called blastomeres
- Each cell touches the zona pellucida

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13
Q

When does the zygote become a morula

A

Zygote becomes a morula once it has reached the 16 cell stage.

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14
Q

What happens once the zygote has become a morula?

A

The cells reorganise themselves. There is an inner core of cells and an outer superficial layer of cells.

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15
Q

What do the inner core and outer superficial layer of cells go on to form after the morula?

A
  • The inner core of cells - forms the embryo proper
  • The outer layer of cells - extra-embryonic membrane
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16
Q

How is a blastocyte formed from a morula?

A

Cells on the outside pump fluid into the embryo to form a blastocyst cavity.
The inner cell mass becomes embryonic stem cells.
The superficial layer of cells become trophoblasts.

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17
Q

What happens during blastocyte hatching?

A

The blastocyte hatches out of the zona pellucida and starts to grow.

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18
Q

What happens during implantation of the blastocyte?

A

The hatched blastocyte implants into the uterine wall for access to nutrition and to excrete waste.

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19
Q

What happens when the trophoblast cells come into contact with the uterus?

A

They start to divide and start to invade the endometrium.

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20
Q

When the trophoblast cells invade the endometrium, they form 2 layers - what are the layers called?

A

1) Cytotrophoblasts (inner, mononucleated cells)
2) Syncynctiotrophoblasts (outer, multinucleated syncynctium)

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21
Q

The inner cell mass forms 2 layers - what are they called?

A
  • The epiblast: Columnar cells adjacent to the syncynctiotrophoblasts
  • The hypoblast: Cuboidal cells facing the blastocyst cavity
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22
Q

What is gastrulation?

A

A process where a single layer gives gives rise to 3 distinct layers.

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23
Q

Vertebrates have 3 germ layers - what are their names?

A

1) Ectoderm (outer layer)
2) Medoderm (middle layer)
3) Endoderm (inner layer)

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24
Q

What part of the blastula embryo is responsible for forming all 3 germ layers

A

The epiblast is responsible for forming all 3 germ layers

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25
Q

Which layers come from where?

A

The mesoderm and the endoderm develop from the epiblast. The cells remaining in the epiblast form the ectoderm.

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26
Q

How does a blastula form a gastrula?

A

Cells in the middle of the epiblast converge to the middle of the disk to form the primitive streak. This begins at the posterior end (tail) an then extends to the anterior end (head)

Cells continually move from the edges to the midline and ingress through the primitive streak.

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27
Q

How does the endoderm form from the epiblast?

A

The endoderm is formed from the first cells that ingress through the primitive streak.
The cells drop down to contact the hypoblast and then form a sheet of cells - the endoderm.

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28
Q

How is the mesoderm formed from the epiblast?

A
  • The mesoderm is formed from the next lot of cells that ingress through the primitive streak
  • These cells form a mass of cells between the endoderm and the epiblast
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29
Q

What is the node and how is it formed?

A

The node is a knot of dividing stem cells formed as the cells condense at the anterior end of the primitive streak.

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30
Q

What happens to epiblast cells that ingress through the node?

A

Epiblast cells that ingress through the node migrate anteriorly to form the sturctures of the head.

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31
Q

What is the regressing node?

A

The regressing node is formed as the node at the end of the primitive streak starts to regress posteriorly.

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32
Q

What happens to cells that ingress through the regressing node?

A

The cells that ingress through the regressing node are pushed down into the mesoderm layer.
The cells that gastrulate through the regressing node only ever form mesoderm cells that go on to form the notochord and somites.

33
Q

What is the definition of primary gastrulation?

A

Primary gastrulation = gastrulation through the primitive streak and through the node.
Can only make enough tissue for the head, body and hindlimb - not enough stem cells to differentiate into the tail.

34
Q

What is the tailbud?

A

A knot of stem cells at the posterior end of the primitive streak.

35
Q

What is the definition of secondary gastrulation?

A

Gastrulation through the tail bud (forms mesoderm cells of the posterior notochord and somites).

36
Q

What parts of the developing embryo are responsible for forming the CNS and PNS?

A
  • CNS (spine and brain) formed from the neural tube
  • PNS (Sensory, enteric, sympathetic, parasympathetic) formed from the neural crest
37
Q

From which germ layer does the neural tube develop?

A

Neural tube develops from the ectoderm

38
Q

What does the neural crest form from?

A

Forms from the dorsal part of the neural tube

39
Q

What is the definition of neurulation?

A

Neurulation = the process by which the neural tube forms from the ectodermal layer.

(Ectoderm formed from the cells that remain in the epiblast during gastrulation)

40
Q

What are the 4 basic steps of neurulation?

A

1) Shaping and folding SLEEP
2) Elevation EAT
3) Convergence COOK
4) Closure CHICKEN

41
Q

What happens during neurulation stage 1, shaping and folding?

A

Shaping: Ectoderm layer thickens towards the edges by changes in shape of cells
Folding: Cells along the midline form a hinge by attaching to the notochord.

The plate is now called the neural groove

42
Q

What happens during neurulation stage 2, elevation?

A

Ectoderm on either side of the neural groove push towards the centre, causing the centre to deepen and the edges to lift up.

43
Q

What happens during stage 3 of neurulation, convergence?

A

The dorsolateral hinge point (DLHP) forms, which makes the neural groove bend at the top.

44
Q

What happens during stage 4 of neurulation, closure?

A

The edges of the neural groove fuse and the ectoderm grows over the top.

PSA: Once the tube is fully closed, and a layer of tissue fully grows over the top, that layer is now called the epidermis.

45
Q

What condition can result from failed closure of the caudal neural tube?

A

Spina Bifida

46
Q

What condition can result from failed closure of the cranial neural tube?

A

Exencephaly

47
Q

Why is folic acid important during embryonic development

A

A lack of folic acid will cause incomplete and incorrect closure of the neural tube.

48
Q

What results from from primary neurulation

A

Cranial neural tube is formed as a result of primary neurulation.

49
Q

How is the caudal neural tube formed?

A

Caudal neural tube is formed from secondary neurulation.

50
Q

How is the medullary chord formed?

A

Medullary chord is formed when mesenchymal cells form a solid rod.

(Mesenchymal cells = stem cells that form from the mesoderm)

51
Q

How does a lumen form in the medullary chord?

A

Lumen form by cavitation (cavities form in the chord and eventually all fuse together)

52
Q

Where do the neural crest cells originate from?

A

Cells originate from the junction of the epidermis and the neural plate (the crest neuroectoderm).

53
Q

What happens when the epidermis contacts the crest neuroectoderm?

A

This induces an epithelial to mesenchymal transition within the crest neuroectoderm.

54
Q

What happens to neural plate cells that break away from the neural plate?

A

They form the neural crest.

55
Q

What derives from the neural crest?

A
  • PNS
  • Pigment Cells
  • Bone, cartilage and connective tissues in the head.
56
Q

What does the ANS allow?

A

It is an unconscious system that allows the flow of information from the CNS to the PNS.

57
Q

What is the axial musculoskeletal system?

A

Axial musculoskeletal system includes the vertebrae and the ribs (central body trunk), the muscles attached to them, and the dermis overlying them.

58
Q

What three main components do somites form?

A
  • Axial skeleton
  • Skeletal muscle
  • Dermis
59
Q

Where are somites located?

A

Somites are located on either side of the neural tube

60
Q

When does the paraxial mesoderm form?

A

Forms during gastrulation.

61
Q

What is the name of the mesenchymal tissue that forms somites?

A

Pre-somatic mesoderm forms somites.

62
Q

What happens at the cranial end of the pre-somatic mesoderm?

A

At the cranial end of the pre-somatic mesoderm, somites form.
At the caudal end cells continue to develop, lengthening the region.

63
Q

How many somites does it take to form one singular vertebra?

A

One pair of somites forms one vertebra.

64
Q

How long does it take for one pair of somites to segment from the pre-somatic mesoderm?

A

90 minutes

65
Q

Segmentation of the pre-somatic mesoderm is dependent on a molecular clock, what is the name of this molecular clock?

A

Molecular clock = a gene called Hairy.

66
Q

What happens at the cranial end of the pre-somatic mesoderm in order for somites to form?

A

Cells at the cranial end of the pre-somatic mesoderm undergo a mesenchymal to epithelial transition to form somites.

67
Q

Where are the most developed somites found?

A

Cranial somites are always more developed than caudal somites

68
Q

What 3 tissues can the somite form?

A

Sclerotome
Myotome
Dermatome

69
Q

What part of the body is formed from the sclerotome?

A

The axial skeleton (vertebrae and ribs)

70
Q

What must be formed from the somite before the myotome and dermatome can form?

A

The dermatomyotome

71
Q

What is formed from the myotome and the dermatome?

A

The myotome forms skeletal muscles (body and limbs)
The dermatome forms the dermis

72
Q

How and where is the epithelial ball (the somite) formed?

A

The pre-somatic mesoderm undergoes a mesenchymal to epithelial transition in caudal, immature somites.

73
Q

How and where is the sclerotome formed?

A

In maturing cranial somites, the ventromedial portion of the somites undergoes an epithelial to mesenchymal transition to form the sclerotome.

74
Q

In the same somite, the dorsal aspect remains epithelial and is called the dermomyotome, what do the dermomyotomal cells then go on to form?

A

Dermomyotomal cells form a new layer - the myotome.

75
Q

How is the dermatome formed?

A

Once all of the myotomal cells have ingressed from the dermomyotome, the cells remaining in the dermomyotome become the dermatome.

76
Q

In what somites does the sclerotome re-segment?

A

In the cranial-most somites.

77
Q

What is the first step of re-segmentation in the sclerotome?

A

A fissure develops in the middle of each somite between the anterior (front) and posterior (back) half.

78
Q

What happens after a fissure had formed between the anterior and posterior halves?

A

The posterior part of one sclerotome fuses with the anterior half of one of the adjacent sclerotome

79
Q

What does the sclerotome encase?

A

Encases the neural tube and sclerotome. It differentiates first into cartilage and then bone, forming vertebrae.

PRIS (CLB) (16 decks)

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