embryology 1

Question 1

what are structures of the H+N very sensitive to throughout development?

Answer 1

teratogens e.g. thalidomides

Question 2

where does primitive pharynx develop from?

Answer 2

crania diverticulum of the primitive gut tube

out-growth at the head of the primitive gut tube

Question 3

by week 4, how is the embryonic head like?

Answer 3

has a face, but no distinguishing external features

is half the length of the body

Question 4

what are the pharyngeal arches?

Answer 4

a system of mesenchymal proliferations in the neck region (cervical) of the embryo
consists of core of proliferating mesenchyme cells, covered by ectoderm on outside surface and endoderm on inside surface

Question 5

where are pharyngeal arches derived from?

Answer 5

paraxial (next to neural tube) and lateral plate mesoderm (somatic = top, splanchnic = bottom)
some contributions from neural crest cells (neural plate border, migrate before neural tube closes)

Question 6

what are the main derivatives of the pharyngeal arches?

Answer 6

many systems of the body esp. brain (paraxial mesoderm), CVS (heart and great vessels)
special sensory organs (e.g. eyes, nose)

Question 7

where does the pharynx extend?

Answer 7

from base of skull (mid head) to inferior border of cricoid cartilage (C5) of the larynx

Question 8

how can the pharynx be divided?

Answer 8

nasal (superior to soft palate)
oral (soft palate to tip of epiglottis (larynx))
hypopharyngeal (laryngopharynx): posterior to larynx

Question 9

what does each pharyngeal arch (paired body segments) consist of?

Answer 9

muscular component
cartilage component
cranial nerve (5,7,9,10)
aortic artery

Question 10

how many pharyngeal arches are there?

Answer 10

5 in total (1-4, 6)

progresively smaller caudally

Question 11

what is between the pharyngeal arches?

Answer 11

endoderm = pouch
ectoderm = cleft (abnormalities can arise)

Question 12

what is at the cranial and caudal ends of the pharyngeal arches?

Answer 12

cranial: stomadeum (mouth) - where the buccopharyngeal membrane (avascular, ischaemic) exits
caudually: heart bulge (eventually migrates to thorax)

Question 13

what forms at the anterior end of the pharyngeal arches?

Answer 13

neural tube - to form the brain (3 buldges: primary brain vesicles):
forebrain, midbrain, hindbrain

Question 14

what supplies the pahryngeal arches?

Answer 14

basket like arrangement of blood vessels

close association of nerves with arches

Question 15

what lies in the floor of the pharynx?

Answer 15

aortic sac

Question 16

what are the arteries supplying the 5 arches?

Answer 16

1/2 arch: arteries disappear

3rd: ICA (to head)
4th: L (arch of aorta), R (brachiocephalic trunk)
6: pulmonary arch (to lungs)

Question 17

what do each pharyngeal arch develop?

Answer 17

a neural crest - derived cartilage bar
1: Meckel's
2: Reichet's
4+6: cartilage of LARYNX (the 9 cartilages - 3 single, 3 pairs)
(Ph A 3 no cartilage bar)

Question 18

where are the cranial nerves derived from?

Answer 18

all from MID-brain / HINDbrain (forebrain forms pituitary gland)
APART from CN I + II (extension of brain meninges, has CSF)

Question 19

how many CN nerves are there associated with the arches?

Answer 19

5 arches (1,2,3,4,6)
4 nerves (5,7,9,10)
CN XI and XII have relationship with pharyngeal arch system