Embryo-Pharyngeal Arches

Question 1

Ecoderm germ layer contributions to pharyngeal arches

Answer 1

Ectoderm–> groove (external auditory meatus, cervical sinus)

Mesenchyme (NCC) and Mesoderm–> muscles, A, N

Endoderm–> pouch (organs)

Membrane: 1 cross-section encompassing all layers

Question 2

Role of NCC in pharyngeal arches

Answer 2

form CT in head including dermis and smooth muscle of blood vessels

Question 3

Types of mesoderm in pharyngeal arches

Answer 3

Paraxial: muscles except extra-ocular

Lateral plate: endothelium that lines blood vessels in face

Prechordal plate: extra-ocular muscles

Question 4

When do the pharyngeal arches form?

Answer 4

Week 4

Question 5

Cleft/Groove vs Membrane

Answer 5

cleft/groove: ectoderm surrounding the arch

membrane: basically a cross-section of an arch with a section of ectoderm and endoderm

Question 6

Describe pharyngeal membranes and its derivative(s).

Answer 6

Membrane (ectoderm, middle arch, endoerm)

quickly infiltrated by mesenchyme (NCC)–> tympanic membrane

Question 7

Derivative(s) of pharyngeal ectoderm

Answer 7

External acoustic meatus

grooves 2-4 are in cervical sinus–>closes off during development

common birth defects involve 2nd groove

Question 8

Skeletal/cartilage derivatives of PA 1 mesoderm

Answer 8

Meckel's cartilage 
   (degenerates--> 
   placeholder for 
   mandible)
Malleus
Incus
Mandible
Sphenomandibular L
Anterior L of malleus

Question 9

Skeletal/cartilage derivatives of PA 2 mesoderm

Answer 9

Reichert's cartilage 
    (will degenerate and 
    contribute to below)
Stapes
Styloid process of 
   temporal bone
Lesser cornu of hyoid
Stylohyoid L

Question 10

Skeletal/cartilage derivatives of PA 3 mesoderm

Answer 10

Greater cornu of hyoid

Question 11

Skeletal/cartilage derivatives of PA 4 mesoderm

Answer 11

Laryngeal cartilage

Epiglottis

Question 12

Skeletal/cartilage derivatives of PA 6 mesoderm

Answer 12

Laryngeal cartilage

Question 13

PA 1 muscular derivatives

Answer 13

muscles of mastication (CN V3)

Question 14

PA 2 muscular derivatives

Answer 14

muscles of facial expression (CN VII)

Question 15

PA 3 muscular derivatives

Answer 15

Stylopharyngeus M (CN IX)

Question 16

PA 4 muscular derivatives

Answer 16

Pharyngeal Constrictor Ms (CN X)

Question 17

PA 6 muscular derivatives

Answer 17

Intrinsic muscles of larynx (CN X)

Question 18

PA 1 innervation

Answer 18

CN V- Trigeminal

Sensory of head and neck

Motor for muscles of mastication

Question 19

PA 2 innervation

Answer 19

CN VII- Facial

Muscles of facial expression

Question 20

PA 3 innervation

Answer 20

CN IX- Glossopharyngeal

Stylopharyngeus M

Question 21

PA 4 innervation

Answer 21

CN X- Vagus

Superior laryngeal N
   Internal branch:
     sensory above cord
   External branch:
      cricothyroid M

Recurrent laryngeal N
–> Pharyngeal Branch

Levator veli palatine
Pharyngeal
constrictor Ms

Question 22

PA 6 innervation

Answer 22

CN X- Vagus

Recurrent laryngeal N
    Inferior laryngeal N 
       Intrinsic muscles of 
        larynx, sensory 
        below cord

Question 23

PA 1 Endodermal derivative(s)

Answer 23

tympanic cavity
mastoid antrum
Eustachian tube

tympanic membrane via 1st membrane derivative

Question 24

PA 2 Endodermal derivative(s)

Answer 24

tonsillar sinus

tonsillar lympoid tissue

Question 25

PA 3 Endodermal derivative(s)

Answer 25

inferior parathyroid gland thymus BOTH MOVE SOUTH

Question 26

PA 4/6 Endodermal derivative(s)

Answer 26

superior parathyroid gland ultimobranchial body--> thyroid gland

Question 27

Tonsils Development

Answer 27

PA 2 endoderm proliferation--> tonsillar epithelium--> mesenchyme differentiation--> lymphoid nodules and tonsillar sinus

Question 28

Thyroid Development

Answer 28

PA 4 endoderm--> ultimobranchial body--> thyroid gland Thyroid primordium (24 days) descends in neck with tongue growth, connected by thyroglossal duct--> degenerate--> patent airway

Question 29

Parathyroid Development

Answer 29

``` PA 4 dorsal endoderm----> superior parathyroid glands ultimobranchial body fuses with thryoid gland to make parafollicular cells ``` PA 3 dorsal endoderm----> inferior parathyroid glands

Question 30

Thymus Development

Answer 30

PA 3 ventral endoderm--> thymic primordium Grow into surrounding mesenchyme to make thymic lobules lobules arranged around central point--> thymic corpuscles Form reticulum for housing lymphocytes Not complete at birth, replaced with adipose tissue in adult

Question 31

First Pharyngeal Arch Syndrome

Answer 31

Abnormal development: Malformation of eyes, ears, mandible, palate -->insufficient migration of NCC during 4th week

Question 32

Treacher-Collins Syndrome

Answer 32

Mandibulofacial dysostosis Malar hypoplasia--> down-slanting features, defects of lower eyelids, deformed ears AD mutation in TCOF1, increased apoptosis of NCC

Question 33

Pierre Robin

Answer 33

De novo Hypoplasia of mandible and cleft palate Defects of eyes and ears micrognathia (small mandible)--> posterior displacement of tongue---> obstruction of closure of palate--> BL cleft palate

Question 34

DiGeorge Syndrome

Answer 34

Breakdown of signaling form PA endoderm to NCC Agenesis of thymus and parathyroid Congenital hypoparathyroidism Shortened upper lip, low set and notched ears Nasal cleft Thyroid hypoplasia Cardiac abnormalities COMMON, VARYING SEVERITIES

Question 35

Agenesis of thyroid gland

Answer 35

Congenital abnormality d/t abnormal migration of NCC or failure of thyroid primordium to form

Question 36

Cervical cyst

Answer 36

Remnant of cervical sinus (ectoderm) or 2nd pharyngeal groove --->covered with skin but not completely closed inside Slow to enlarge inferior to angle of mandible Fluid cellular debris pile up, painless

Question 37

Cervical sinus congenital abnormality

Answer 37

Failure to close or 2nd pharyngeal groove to degenerate (partial closing) Discharge of mucus BL, commonly associated with auricular sinuses Infection risk

Question 38

Cervical fistula

Answer 38

Abnormal canal into tonsillar sinus that extends out of neck ---> persistence of 2nd pharyngeal groove and pouch Open from pharynx to skin, leaks mucus from oral cavity out to skin