Embryology of the Pharyngeal apparatus

Question 1

What does the Pharyngeal Apparatus give rise to

Answer 1

consists of pharyngeal arches (PA), pouches, grooves (clefts) and membranes

Contribute to the formation of nasal cavities, mouth, larynx, pharynx, and neck

Question 2

When do the Pharyngeal arches develop and where?

Answer 2

4th week as neural crest cells migrate into the future head and neck

1st pair of arches (primodial jaws) appear lateral to developing larynx

Arches 2-4 appear as ridges on each side of future neck and head regions

5/6 arches are rudimentary and not visible

Question 3

What does each pharyngeal arch consists of embrylogically?

Answer 3

core of mesoderm and mesenchyme

covered externally by Ectoderm

and covered internally by endoderm

(mesenchyme is derived from migratory NCC)
(head mesoderm forms from paraxial mesoderm)

Question 4

What do the Pharyngeal arches give rise to and function?

Answer 4

Support the lateral walls of the primordial pharynx

give rise to the prominences of tissue that contribute to craniofacial development

Question 5

What are the 4 embryological Pharyngeal arch components and what do they give rise to

Answer 5

NCC derived Mesenchyme: forms all the connective tissue in the head including the dermis and smooth muscle

Paraxial Mesoderm: Populates each arch to form Pharyngeal arch musculature

Lateral Plate Mesoderm: Angioblasts that differentiate into the endothelium

Prechordal Plate Mesoderm: Extraocular musculature

Pharyngeal endoderm plays an essential role inregulating the development of the arches

Question 6

The pharyngeal arch contains 4 st ructures

Answer 6

Cartilaginous rod: forms the skeletal element

Muscular component: differentiates into the muscles in the head and neck

Cranial Nerves: sensory and or motor components

Arch Artery: arising from the truncus arteriosus of primodial heart, it passes around the primordial pharynx to enter the dorsal aorta

Question 7

Pharyngeal Arch 1: Cartilage

Answer 7

Meckels cartilage

Dorsal portion forms the malleus and incus

Perichondrium: makes anterior ligament of malleus and sphenomandibular ligament

Ventral parts: primordium (model) of the mandible the bone will form laterally to meckels

Question 8

Pharyngeal Arch 2: Cartilage

Answer 8

Riecherts Cartilage

Dorsal region contributes to the stapes and styloid process of the temporal bone

Perichondrium: stylohyoid ligament

ventral end ossifies and forms the lesser cornu/horn of hyoid bone

Question 9

Pharyngeal Arch 3: cartilage

Answer 9

Ossifies and forms the greater cornu of hyoid bone

Body of the Hyoid bone is formed by the hypopharyngeal eminence via PA3 and PA4

Question 10

Pharyngeal Arch 4 cartilages

Answer 10

laryngeal cartilages including the epiglottis (NCC derived

Question 11

Pharyngeal Arch 6 cartilages

Answer 11

Laryngeal cartilages, but orgin is uncertain

Question 12

Pharyngeal Arch 1 Muscles

Answer 12

Muscles of Mastication (CN V)

Question 13

Pharyngeal Arch 2 Muscles

Answer 13

Stapedius and muscles of facial expression (CN VII))

Question 14

Pharyngeal Arch 3 Muscles

Answer 14

Stylopharyngeus Muscle (CN IX)

Question 15

Pharyngeal Arch 4 Muscles

Answer 15

Cricothyroid, levator veli palatini, constrictors of pharynx (CN X)

Question 16

Pharyngeal Arch 6 muscles

Answer 16

Intrinsic muscles of the larynx (CN X)

Question 17

What nerve supplies the 1st PA

Answer 17

Trigeminal Nerve: supplies the first arch

principle sensory to the head and neck

Motor nerve for the muscles of mastication

Question 18

What nerve supplies the 2nd PA

Answer 18

Facial Nerve which will supply the muscles of facial expression

Question 19

What nerve supplies the 3rd PA

Answer 19

Glossopharyngeal nerve (CN IX)

also supplies the stylopharyngeus m

Question 20

What nerve supplies the 4th-6th Arch

Answer 20

Vagus Nerve (CN X)

4th arch supplied by the superior laryngeal branch of CN X and its recurrent laryngeal branch

also supplies the constrictors of pharynx and intrinsic muscles of the larynx

Question 21

what do the arch arteries arise from?

Answer 21

5 pairs of arteries arise from the Aortic sac

it is a basket like structure arising from the dorsal aorta that gets remodeled into the great arteries of the thorax and head/neck

arteries arising from the 1st -3rd aortic arch are bilateral and 4th and 6th are asymmetrical

come from mesoderm

Question 22

What are Pharyngeal Grooves and what do they give rise to

Answer 22

Located between the pharyngeal arches

covered with ectoderm

first groove gives rise to the external acoustic meatus

grooves 2-4 lie in the cervical sinus and these will eventually go away

Question 23

What are Pharyngeal pouches

Answer 23

Pharyngeal endoderm lines the pharynx internally and create pharyngeal pouches

5 pairs of pouches that develop between the craniocaudal sequence between the arches

Question 24

Cervical Cysts branchial anomaly

Answer 24

Remnants of cervical sinus and or the 2nd groove

persist to form a slowly enlarging painless free lying cyst in the neck inferior to the angle of the mandible

Accumulation of fluid and cellular debris derived from desquamation of their epithelial linings

Question 25

Cervical sinus branchial anomaly

Answer 25

failure of the 2nd PA groove and cervical sinus to obliterate detected due to discharge of mucus typically bilateral and commonly associated with auricular sinuses

Question 26

Cervical Fistula branchial anomaly

Answer 26

Abnormal canal that opens into the tonsillar sinus and externally in the side of the neck persistence of parts of 2nd groove and pouch

Question 27

What is the pharyngeal membrane, and what gives rise from the pharyngeal membrane

Answer 27

form where the pouch endoderm contacts ectoderm of the pharyngeal quickly infiltrated by mesenchyme 1st pharyngeal membrane plus the intervening mesenchyme forms the tympanic membrane

Question 28

What does the first pouch form

Answer 28

expands into the tubotympanic recess creating the tympanic cavity and the mastoid antrum elongates to form pharyngotympanic tube

Question 29

What does the 2nd pouch form

Answer 29

Portion of the tonsillar sinus Endoderm proliferates to form the tonsillar epithelium mesenchyme differentiates to form the lymphoid nodules of palatine tonsil

Question 30

What does the 3rd pouch form

Answer 30

Dorsal portion forms the inferior parathyroid gland ventral portion forms the thymus (this will caudally migrate due to growth of brain and cardiac regions

Question 31

What does the 4th pouch form

Answer 31

Dorsal portion differentiates into the superior parathyroid glands Ultimobranchial body fuses with the thyroid gland to give rise to the para follicular cells (this will stay put as the contents of the third pouch will migrate inferiorly past)

Question 32

Thymus development, and the function of the three epithelial cords

Answer 32

Thymic primordium develops from PA3 endoderm composed of epithelial cords these function: grow into surrounding mesenchyme- thymic lobules Become arranged around a central point- forming thymic corpscule Form an epithelial reticulum for housing lymphocytes growth is still very active during childhood

Question 33

Thyroid Gland Development

Answer 33

First endocrine gland to develop - thyroid primordium Forms from a median endodermal thickening in floor of primordial pharynx descends in the neck with tongue growth and passes ventral to developing hyoid bone and laryngeal cartilages connected to tongue by a narrow tube- thyroglossal duct but this will then disintegrate

Question 34

First Arch Syndromes

Answer 34

abnormal development of the first arch malformation of the eyes, ears, mandible, and palate results from insufficient migration of NCC into the 1st arch during 4th week

Question 35

Treacher-Collins Syndrome (mandibulofacial dysostosis

Answer 35

Malar hypoplasia with down slanting palpebral fissures, defects of lower eyelids, deformed external ears, and sometimes middle and internal ears Autosomal dominant disorder due to mutations in Treacher Collins Franceschetti syndrome 1 gene (TCOF 1) encodes for the protein TREACLE involved in ribosome biogenesis truncated in TCS leading to increased apoptosis of Cranial NCC

Question 36

Pierre Robin sequence

Answer 36

hypoplasia of the mandible, cleft palate, and defects of the eyes and ears initiating defect is a small mandible (micrognathia) which results in posterior displacement of the tongue and obstruction of full closure of the palate resulting in bilateral cleft palate

Question 37

Agenesis of thyroid gland

Answer 37

absence of a thyroid gland or one of its lobes

Question 38

Thyroid hemigenesis

Answer 38

unilateral failure of formation usually the left lobe mutations in the receptor for the thyroid stimulating hormone are likely involved

Question 39

DiGeorge Syndrome

Answer 39

Breakdown of signaling from the PA endoderm to NCC agenesis of the thymus and the parathyroid glands congenital hypothyroidism shortened philitrum of upper lip, low set and notched ears nasal clefts, thyroid hypoplasia cardiac abnormalities due to defects of the aortic arch