DONE Embryology 2

Question 1

What is the embryonic period?

Answer 1

Weeks 3-8
Period of greatest change
Major structures + systems formed
Greatest risk of congenital malformation (teratogenesis) due to drug/environmental exposure

Question 2

What are the 4 key processes in the embryonic period?

Answer 2

Gastrulation > Neurulation > segmentation > folding

Question 3

Primitive streak

Answer 3

In 3rd week appears on dorsal surface of epiblast (end point when embryos can be studied)

Question 4

What occurs during gastrulation?

Answer 4

Epiblast cells multiply + migrate into epithelial layer
Displace hypoblast
Form trilaminar disk (all derived from epiblast = ectoderm, mesoderm, endoderm)

Question 5

Ectoderm

Answer 5

Organs + structures in contact with outside world

E.g. nervous system, epidermis

Question 6

Mesoderm

Answer 6

Supporting tissues

E.g. muscle, bone, vascular system (heart)

Question 7

Endoderm

Answer 7

Internal structures

E.g. epithelial lining of GI tract, respiratory tract

Question 8

What is situs inversus?

Answer 8

Complete mirror-image viscera (heart in right-side chest, not left)
Due to immotile cilia (similar symptoms to CF)

Question 9

How is left-right asymmetry ensured?

Answer 9

Ciliated cells @ primitive node signal for ‘left-sideness’ etc

Question 10

Notochord

Answer 10

Solid rod of cells in midline, signalling role

Question 11

What occurs in neurulation?

Answer 11

Notochord causes ectoderm to differentiate into neuroectoderm
Causes ectoderm to thicken to form slipper-shaped neural plate (edges elevate + curl = neural tube = nervous system)

Question 12

What does the somatic mesoderm form?

Answer 12

Diaphragm + limb muscles (is the higher mesoderm bit)

Question 13

What does the splanchnic mesoderm form?

Answer 13

Muscles of heart + viscera

Intraembryonic coelom in between this + above somatic mesoderm = forms body cavities

Question 14

Somites

Answer 14

Embryonic body segments (31 total) formed from paraxial mesoderm

Question 15

Somite derivatives

Answer 15

Dermatome = skin section, dermis
Myotome = muscle section
Sclerotome = hard tissue section, bones

Question 16

What occurs in folding?

Answer 16

Cephalocaudal folding driven by neural tube growth

Folds endoderm INSIDE, only ectoderm OUTSIDE

Question 17

What does folding achieve?

Answer 17

Draws together margins of the disk
Creates ventral body wall
Pulls amniotic membrane around disk

Question 18

By the end of the 4th week what has occurred?

Answer 18

Nervous system started to form
Segments appeared
Embryo folded