Development of the pharyngeal arches and the face :/

Question 1

what is important in the head/neck region

Answer 1

neural crest cells

Question 2

where is mesoderm dounf

Answer 2

between endo and echo derm

Question 3

what does endoderm form

Answer 3

gut lining and glands

Question 4

what is outside of embyro

Answer 4

ectoderm

forms appendages such as skin

Question 5

what is present 3.5 weeks post conception

Answer 5

frontonasal process
pharyngeal/branchail branches 
hindlimb bud
somites
occpital somites

Question 6

what does the frontonasal process contain

Answer 6

forebrain

Question 7

which pharyngeal branches are visible and where are they

Answer 7

1-4

pressed up against the heart (pericardial sac)

Question 8

Hindlimb bud

Answer 8

where arms and legs develop in future

Question 9

somites

Answer 9

areas of high density cells

develop in segmental structures

Question 10

occipital somites

Answer 10

those that become close to the back of the head

Question 11

stomadium

Answer 11

primitive developing mouth

where external ectoderm folds in to meet the endoderm layer

Question 12

how does the stomadium form

Answer 12

• before 4 weeks the ectoderm and endoderm layer are in close proximity
• buccopharyngeal membrane separates the outside of the embryo to the inside, this will break down 4-5 wks
• outside environment passes through the stomodeum into the primitive gut

Question 13

optic placode

Answer 13

where future eyes will be
area of specialised thickened epithelium
interacts with the underlying developing forebrain to delve eyes

Question 14

pharyngeal arches

Answer 14

• 5 and 6 are rarely seen
• 1-4 visible
• These outgrowths are bilateral, come from the side of the embryo and grow towards the midline in pairs
  Arches 4,5,6 fuse together to form a single arch

Question 15

what are the arches separate by

Answer 15

• Arches separated externally by clefts

- internally separated by pouches that respond with the clefts

Question 16

structure of pharyngeal arches

Answer 16

• outer surface covered by ectoderm
• inner surface lined with endoderm(inner is the middle)
• packed with ectomesenchyme
• each arch has an artery, vein and cranial nerve
• also has a skeletal element
• also a muscle block (in the lower branches more likely to be mesodermal derived rather than endoderm further up)

Question 17

pattern formation of pharyngeal arches

Answer 17

• migration of nerve fibres from the neural tube into the arches is consistent and predictable
• they will always innervate specific muscles and regions of skin and mucosa

Question 18

cranial nerves innervation with pharyngeal arches

Answer 18

1) 1st arch innervated by trigeminal
2) 2nd arch by facial
3) 3rd arch by glossopharyngeal
4) 4th arch by vagus

Question 19

what is expressed in each arh

Answer 19

Hox genes

- cells know where they should be and what to form

Question 20

what do the patterns of hox genes do

Answer 20

Patterns of hox gene expression within the midbrain and hindbrain set up identity

• as cells migrate from the neural tube they keep this pattern
• regulates movement and differentiation of the cells