Embryogenesis

Question 1

What is the blastocyst?

Answer 1

Ball of 50-150 cells encased in a membrane

4-5 days post-fertilisation

Question 2

What are the two cell populations which develop from the blastocyst?

Answer 2

Inner cell mass

Trophectoderm

Question 3

What is generated from the inner cell mass?

Answer 3

Embryo

Extra-embryonic tissue

(Source of embryonic stem cells)

Question 4

What is generated from the trophectoderm?

Answer 4

Extra-embryonic tissue only

Question 5

What is the fluid-filled cavity of the blastocyst called?

Answer 5

Blastocele

Question 6

What are the two properties of embryonic stem cells?

Answer 6

Can divide to renew themselves without losing pluripotency

Can differentiate into all cells of the body

Question 7

When does implantation begin?

Answer 7

6 days post-fertilisation

Question 8

What is implantation?

Answer 8

Trophoblasts make contact with uterine wall and infiltrates/implants

Question 9

What is gastrulation?

Answer 9

Generation of the three germ layers

Question 10

What happens to the inner cell mass before gastrulation?

Answer 10

Flattens into a 2-layered disc

Question 11

What is derived from the inner cell mass when it flattens?

Answer 11

Epiblast

Hypoblast

Question 12

What is generated from the epiblast?

Answer 12

Embryo

Question 13

What is generated from the hypoblast?

Answer 13

Extra-embryonic tissue

Question 14

Where and when does the primitive streak form?

Answer 14

At one end of epiblast

At 12 days

Question 15

What is the primitive streak?

Answer 15

Where cells ingress through to form endoderm and mesoderm (site of gastrulation)

Question 16

What happens during gastrulation?

Answer 16

Cells in epiblast migrate towards primitive streak

At 14-15 days, ingressing cells form endoderm which integrates with hypoblast

At 16 days, ingressing cells form mesoderm which lies above endoderm

Question 17

When is the endoderm formed?

Answer 17

14-15 days

Question 18

When is the mesoderm formed?

Answer 18

16 days

Question 19

Describe the cells in each of the germ layers.

Answer 19

Ectoderm: tall columnar

Mesoderm: flat, fibroblast-like with protrusions

Endoderm: cuboidal

Question 20

What structures are derived from the ectoderm?

Answer 20

Skin

Nervous system

Question 21

What structures are derived from the mesoderm?

Answer 21

Vertebral column

Skeleton

Skeletal muscle

Circulatory system

Blood

Kidneys

Question 22

What structures are derived from the endoderm?

Answer 22

Gastrointestinal tract

Question 23

What structures are derived from the endoderm and mesoderm?

Answer 23

Lungs

Pancreas

Liver

Thymus

Question 24

Give the names of the regions which describe the medial-lateral axis.

Answer 24

Axial

Paraxial

Intermediate

Lateral plate

Question 25

What is derived from the axial mesoderm?

Answer 25

Notochord - centre of vertebral disc Prechordal mesoderm - (some) muscles in head

Question 26

What is derived from the paraxial mesoderm?

Answer 26

Somites in trunk - skeleton, muscles, dermis

Question 27

What is derived from the intermediate mesoderm?

Answer 27

Kidneys Part of genital system

Question 28

What is derived from the lateral plate mesoderm?

Answer 28

Viscera Inner lining of body wall Dermis

Question 29

What determines a cell's final position in the medial-lateral axis?

Answer 29

Position of the cell along the primitive streak

Question 30

What does the position of a cell along the primitive streak determine?

Answer 30

The cell's final position in the medial-lateral axis

Question 31

Where do the cells at the tip of the primitive streak move into (mesoderm)?

Answer 31

Notochord - axial

Question 32

What is the equivalent to the medial-lateral axis?

Answer 32

Dorsal-ventral axis

Question 33

What is the equivalent of the rostral-caudal axis?

Answer 33

Head-tail axis

Question 34

What determines a cell's position along the rostral-caudal axis?

Answer 34

Order in which it emerges from the primitive streak

Question 35

What does the order in which cells emerge from the primitive streak determine?

Answer 35

The cells' position along the rostral-caudal axis

Question 36

Which cells will be most rostral?

Answer 36

Cells which leave the primitive streak first

Question 37

Which cells will be most caudal?

Answer 37

Cells which leave the primitive streak last

Question 38

What is the neural plate?

Answer 38

Origin of CNS

Question 39

What germ layer is the neural plate derived from?

Answer 39

Ectoderm

Question 40

How does the neural plate form the neural tube?

Answer 40

Invagination along midline of neural plate and ectoderm cells elongate Neural folds move towards each other and fuse at hindbrain then zips to close in both directions (neuralation) Separates from surface ectoderm which closes over it

Question 41

How and in what way is the neural tube patterned?

Answer 41

Signals from axial mesoderm Motor neurons formed at ventral end Sensory neurons formed at dorsal end

Question 42

What tissue initiates/signals for the separation of the eye field and when?

Answer 42

Axial mesoderm 19-20 days

Question 43

What causes defects in midline patterning (eg. cyclopsy)?

Answer 43

Mutations in Sonic Hedgehog pathway expressed in axial mesoderm

Question 44

Where does the lateral body wall fuse relative to the neural tube?

Answer 44

Anterior to neural tube with ectoderm on outside

Question 45

Where are the neural crest cells derived from?

Answer 45

Dorsal neural tube

Question 46

What do the trunk neural crest cells form?

Answer 46

Melanocytes Sensory neurons Sympathetic neurons Enteric neurons Glia

Question 47

What do the head neural crest cells form?

Answer 47

Melanocytes Cranial ganglia Craniofacial skeleton Odontogenic mesenchyme (ectomesenchyme)