Embryogenesis

Question 1

How do cells migrate?

Answer 1

Down concentration gradient of growth factors and cytokines

Question 2

What are the three broad periods of gestation?

Answer 2

1. Ovum
2. Embryo
3. Foetus

Question 3

What are the key evens of the ovum period?

fertilisation to the end of the 1st week of gestation

Answer 3

1. Transport of zygote from oviduct to uterus
2. Multiple mitotic cell division
3. Transformation from zygote to morula to blastocyst
4. Hatching of blastocyst out of zona pellucida

Question 4

What is the zona pellucida?

Answer 4

A thick membrane surrounding the blastocyst

Question 5

What is the cluster of cells at the top of the blastocyst referred to?

Answer 5

Inner cell mass (ICM)

Question 6

What are the key events which occur during the 2nd week (embryo stage)?

Answer 6

1. Blastocyst elongation
2. Appearance of germ layers
3. Implantation

Question 7

What are the three germ layers?

Answer 7

1. Ectoderm
2. Mesoderm
3. Endoderm

Question 8

What is the formation of the germ layers called?

Answer 8

Gastrulation

Question 9

What are the key events which occur during the 3rd week (embryo stage)?

Answer 9

1. Ebryonic body established (tail, head and limb buds)

2. Extra-embryonic membranes formed through folding (amnion, chorion, yolk sac and allantois)

Question 10

At what stage of development do organs become functional?

Answer 10

Foetal

Question 11

What does CRL stand for?

Answer 11

Crown to Rump Length (spine length)

Question 12

What can be used to age embryos?

Answer 12

Somite number

Question 13

What does cleavage refer to?

Answer 13

Mitotic division inside the zona pellucida

Question 14

What are the four extra embryonic membranes?

Answer 14

1. Amnion
2. Yolk sac
3. Chorion
4. Allantois

Question 15

What are the cells produced by cleavage called?

Answer 15

Smaller cells called blastomeres.

Question 16

What governs the pattern of cleavage?

Answer 16

Size of yolk. Avians have large yolk and partial cleavage (meroblastic). Mammals have minimal yolk and total cleavage (holoblastic)

Question 17

What is the solid cluster of cells caused by cleavage called?

Answer 17

Morula

Question 18

What are the two changes which differentiate a morula from a blastocyst?

Answer 18

1. Blastomeres loose shape, becoming tightly apposed (compaction)
2. Blastomeres start secreting into the centre of the morula (blastocoel)

Question 19

What is the layer of cells surrounding the blastocoel called?

Answer 19

Tropoblast layer

Question 20

Where does the embryo start developing from?

Answer 20

ICM aka. embryonic disc

Question 21

What are the forces resulting in hatching of the blastocyst from the zona pellucida?

(except for in rodents and horses)

Answer 21

1. Accumulation of fluid
2. Enzymes secreted by the trophoblast layer
3. Blastocyst contration

Question 22

What type of junctions are between cells in the ICM?

Answer 22

GAP junction for cellular communication

Question 23

What type of junctions are between cells in the trophoblast?

Answer 23

Tight junctions for controlled diffusion

Question 24

What does delamination refer to?

Answer 24

Movement of a cell layer away from the ICM

Question 25

How is the hypoblast formed?

Answer 25

Delamination of cells from the ICM, forming a layer of cells inside the trophoblast

Question 26

After delamination of the hypoblast, what is the remaining ICM called?

Answer 26

Epiblast

Question 27

Where is the amniotic cavity formed?

Answer 27

In-between the trophoblast and epiblast layers

Question 28

How is the endoderm layer formed?

Answer 28

First migrating cells of epiblast layer down the primitive streak, which then move laterally

Question 29

How is the mesoderm layer formed?

Answer 29

Second migrating cells of epiblast layer down the primitive streak

Question 30

How is the ectoderm layer formed?

Answer 30

The remaining cells left on the top of the epiblast layer

Question 31

What defines the major body axis during embryogenesis?

Answer 31

Formation of the primitive streak

Question 32

What tissues arise from the ectoderm?

Answer 32

1. Epithelium of skin 2. Nervous tissue 3. Brain and spinal cord 4. PNS

Question 33

What tissues arise from the mesoderm?

Answer 33

1. Connective tissue 2. Muscle 3. Epithelial lining of some organs (cardiovascular, reproductive and urinary systems)

Question 34

What tissues arise from the endoderm?

Answer 34

1. Gastro intestinal tract 2. Epithelial linings of respiratory tract, bladder, middle ear and auditory tube 3. Parenchymal cells of the liver, pancreas, thyroid and parathyroid

Question 35

What is a notochord?

Answer 35

Rod shaped aggregate of cells located cranial to the primitive streak, marks future location of the spinal cord

Question 36

What does the formation of the notochord induce?

Answer 36

Formation of head, nervous system development and somite formation

Question 37

What extra-embryonic membrane is derived from the trophoblast and the mesoderm?

Answer 37

Chorion and amnion

Question 38

What is the function of the chorion?

Answer 38

Mediates attachment to the uterus

Question 39

What extra-embryonic membrane is derived from the endoderm?

Answer 39

Yolk sac

Question 40

What is the function of the amnion?

Answer 40

Fluid filled sac that protects the embryo

Question 41

What extra-embryonic membrane is derived form the primitive gut?

Answer 41

Allantois

Question 42

What is the function of the allantois?

Answer 42

Fluid filled sac that collects waste from the embryo, eventually fuses with chorion to form allantochorionic membrane

Question 43

What is neurolation?

Answer 43

The initial development of the gut, heart and formation of the nervous system

Question 44

What are the structures arised from neurolation?

Answer 44

1. Neural plate and neural 2. Somites 3. Neural tube 4. Neural crest cells

Question 45

What do neural crests form?

Answer 45

Peripheral nervous system

Question 46

What does the neural tube form?

Answer 46

Central nervous system

Question 47

What does the folding of the endoderm form?

Answer 47

Primitive gut tube

Question 48

How are placodes formed?

Answer 48

Thickening of ectodermal cells

Question 49

What do the placodes form?

Answer 49

1. Nasal chambers 2. Lens 3. inner ear (otic)

Question 50

How are pharyngeal arches formed?

Answer 50

Concurrent invagination of surface ectoderm (clefts) and endoderm (pouches)

Question 51

What structures arise from paraxial mesoderm?

Answer 51

Somites

Question 52

What structures arise from intermediate mesoderm?

Answer 52

Urinary and reproductive organs

Question 53

What structures arise from lateral mesoderm?

Answer 53

Body cavities (pleural, pericardial and peritoneal)

Question 54

What structures are derived form the somites?

Answer 54

1. Dermis 2. Axial skeleton 3. Skeletal, cardiac and smooth muscle

Question 55

What is the function of the yolk sac?

Answer 55

Contributes to primitive germ cells

Question 56

Does cleavage of blastomeres increase the size of the morula?

Answer 56

There is no net increase in size. This is because they are constricted by the zona pellucida