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VETS1060 > Embryology > Flashcards

Embryology Flashcards

(52 cards)

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1
Q

What is embryology?

A

The study of embryonic development

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2
Q

What is the set order of embryonic development? (4)

A
  1. Fertilisation
  2. Cleavage
  3. Gastrulation
  4. Organogenesis
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3
Q

What occurs during the fertilisation stage of embryonic development?

A

Fusion of sperm & egg to form a zygote

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4
Q

What occurs during the cleavage stage of embryonic development?

A

Cell divisions to form blastula/blastocyst

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5
Q

What occurs during the gastrulation stage of embryonic development?

A

Blastula rearranges layers of cells to form the gastrula

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6
Q

What occurs during the organogenesis stage of embryonic development?

A

Rudimentary organs form

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7
Q

In which animals do the 4 stages of fertilisation, cleavage, gastrulation and organogenesis occur

A

ALL animals

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8
Q

Despite their varying body plans, what is the same across all animals?

A
  • Basic mechanisms of development
  • Common set of regulatory genes
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9
Q

What is the equivalent of the Tinman gene from Drosophila in vertebrates and what do these genes do?

A

Homologue; regulates position of heart

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10
Q

What are the 3 key events involved in fertilisation?

A
  1. Contact
  2. Acrosomal reaction
  3. Cortical reaction
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11
Q

Briefly explain what happens in the contact stage of fertilisation?

A

Spermatozoon makes contact with
the protective layer (jelly coat, zona pellucida) surrounding the egg

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12
Q

Briefly explain what happens in the acrosomal reaction stage of fertilisation?

A
  • Release of hydrolytic enzymes from acrosome which digest a hole in jelly coat
  • Molecules on sperm bind to receptors on egg
  • Species specific
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13
Q

Briefly explain what happens in the cortical reaction stage of fertilisation?

A
  • Changes at surface of egg prevent further sperm entering – blocks polyspermy
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14
Q

What about the acrosomal reaction stage of fertilisation is an impediment to interspecies breeding?

A

It is species specific

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15
Q

Describe the acrosomal process of the acrosomal reaction in fertilisation

A
  • Actin filaments pierce the jelly coat
  • Proteins on the tip of the acrosomal process bind to receptors on the egg plasma membrane
  • Lock & key method used, especially important in species with external
    fertilisation in water
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16
Q

How does the acrosomal process of fertilisation blocks other sperm from fusing?

A
  • Binding of proteins on acrosomal process to receptors on egg causes fusion of plasma membranes of spermatozoon & egg
  • Fusion triggers opening of Na+ channels
  • Na+ rapidly diffuses into egg
  • Causes depolarisation which blocks other sperm from fusing
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17
Q

Describe the Cortical Reaction in fertilisation

A
  • A longer-lasting block to polyspermy
  • Cortical granules (vesicles beneath plasma membrane of egg) fuse with plasma membrane of the egg
  • Enzymes are released into perivitelline space
  • Vitelline layer lifts away and hardens to form the fertilisation envelope
  • Receptors are clipped off so there is no further binding
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18
Q

What is the perivitelline space?

A

The space between the plasma membrane & outer
vitelline layer called?

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19
Q

Describe the cleavage step of fertilisation

A
  • Succession of rapid cell divisions
  • One large fertilised egg (zygote) becomes many smaller cells called blastomeres
  • First 5-7 divisions produce a hollow ball of cells
  • Blastula (blastocyst in mammals)
  • Ball of cells surrounds a fluid-filled space called the blastocoel
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20
Q

What are the two types of cleavage patterns?

A
  1. Holoblastic
  2. Meroblastic
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21
Q

Which animals use holoblastic cleavage?

Study These Flashcards
A

Therian mammals, amphibians, echinoderms

22
Q

Which animals use meroblastic cleavage?

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A

Monotremes, birds, reptiles, fish, insects

23
Q

What is the difference between holoblastic and meroblastic cleavage?

Study These Flashcards
A
  • Holoblastic have complete division of egg and yolk
  • Meroblastic has partial/incomplete division with no full penetration of the yolk
24
Q

Describe holoblastic cleavage

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A
  • Yolk is concentrated towards one pole (vegetal) with less yolk at opposite (animal) pole creating hemispheres
  • During division, cleavage furrows forms
  • The first cleavage furrow is parallel to the line connecting the poles
  • The second is at right angle to the first
  • 3rd division is equatorial to produce 8 cells
25
Which pole has more yolk at the beginning of holoblastic cleavage?
Vegetal pole
26
What is a cleavage furrow?
An indentation forms that divides the cells in half
27
Describe meroblastic cleavage
- The volume of yolk in vegetal hemisphere so great that cleavage furrows cannot pass through it - Cleavage occurs only in animal hemisphere - In birds, the yolk of the shelled egg is the fertilised egg - Cleavage occurs in blastodisc, generating a multicellular blastoderm
28
What is a blastodisc?
A small disc at the animal pole where cleavage occurs in meroblastic cleavage
29
What is the end result of Holoblastic cleavage?
A ball of cells called the blastula (blastocyst)
30
What is a blastocyst?
A ball of cells at the end og holoblastic cleavage
31
What is the fluid filled space inside the blastula?
The blastocoel
32
What is special about cleavage in mice and humans?
The blastocyst contains a group of cells called the inner cell mass (embryoblast) which forms the embryo and is the source of embryonic stem cells
33
What is the outer layer of cells in cleavage called?
The trophoblast - Does not contribute to the embryo - Forms chorion (placenta)
34
Describe the process of gastrulation
- Gastrulation involves the reorganisation of the cells after cleavage to form a 3-layered embryo
35
What is the result at the end of cleavage?
The embryo consists of a ball of cells with a fluid-filled space in the centre
36
What are the three germ layers?
1. endoderm 2. mesoderm 3. ectoderm
37
What is the role of the embryonic germ layers?
- To contribute to a distinct set of tissues in the animal - Some organs are derived from more than one layer
38
Describe the process of gastrulation in frogs
1. The group of cells on dorsal surface of blastula invaginate to form a small, indented crease called a blastopore 2. Sheet of cells at animal hemisphere migrate by rolling over edge of blastopore to move inside 3. Once inside, they move towards animal pole and are organised into endoderm & mesoderm 4. The cells remaining at animal hemisphere become the ectoderm by spreading over outer surface 5. As more cells continue to enter through enlarging blastopore, a new space starts to form: the archenteron, and the blastocoel becomes smaller 6. Eventually, the endoderm-lined archenteron replaces the blastocoel
39
Describe the process of gastrulation in birds
1. Rather than a hollow ball of cells (ie frog), the avian blastula is a disc of cells atop a yolk mass called the blastoderm 2. Cells of the blastoderm divide to form 2 layers: epiblast and hypoblast with the blastocoel sitting in between 3. The embryo will develop from the epiblast 4. Cells from the epiblast move to the centre of the blastoderm & inwards towards the yolk. This produces a thickening: primitive streak 5. Some cells that have migrated through the primitive streak move downward and form the endoderm, others migrate laterally and form the mesoderm 6. Cells left behind on the surface form ectoderm
40
In frogs, the blastopore that surrounds a plug of yolk-filled cells will form the...
Anus
41
In frogs, the archenteron becomes ...
The cavity of the digestive tract
42
Describe the process of gastrulation in mammals
1. Inner cell mass (embryoblast) forms the embryo 2. Trophoblast forms chorion 3. Trophoblast cells secrete enzymes that facilitate implantation into endometrium of uterus 4. Inner cell mass divides into epiblast & hypoblast 5. Epiblast forms the embryo 6. Cells of epiblast move inward via primitive streak to form mesoderm & endoderm
43
Totipotent cells
- Can form all cell types of the body plus the extraembryonic (placental) tissues - First few divisions after fertilisation: 8-cell stage
44
Pluripotent cells
- Can form all cell types of the body but not the extraembryonic tissues - Cells from the inner cell mass - Embryonic stem cells (ESCs) - Induced pluripotent stem cells (iPSCs) are produced from adult cells via ‘reprogramming’
45
Multipotent cells
- Adult stem cells - Found in bone marrow, adipose tissue - Limited differentiation ability
46
Mesenchymal stem cells (MSCs)
- A type of multipotent stem cell - Cartilage, bone, adipose tissue
47
Describe the process of organogenesis
- Specific regions of the 3 embryonic germ layers give rise to specific organs
48
Neurulation
The development of the central nervous system
49
Describe the process of neurulation
1. Cells from dorsal mesoderm come together to form the notochord 2. Ectoderm above the notochord becomes the neural plate 3. Infolding of the neural folds adjacent to the neural plate generates the neural tube (brain & spinal cord)
50
In vertebrates, 2 types of cells develop near the neural tube:
1. Neural crest cells 2. Somites
51
What are Neural crest cells
- From neural folds - Migrate to many parts of the embryo like neurons, bone, pigment cells
52
What are Somites?
- From mesoderm - Play a major role in organising the segmented structure of body (Vertebrae & associated muscles)

VETS1060 (22 decks)

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