Pharyngeal Apparatus/Embryo

what are components of pharyngeal (branchial) apparatus

pharyngeal arches, pharyngeal pouches, pharyngeal grooves (cleft), and pharyngeal membranes

what tissues line pharyngeal arches

external → ectoderm

internal → endoderm

core → mesenchyme (mesoderm + neural crest)

what structures are found in each pharyngeal arch

cartilage, muscle, aortic arch artery, and cranial nerve

skeletal derivatives of pharyngeal arch 1

malleus

incus

Meckel’s cartilage

sphenomandibular ligament

skeletal derivatives of pharyngeal arch 2

stapes, styloid process, stylohyoid ligament, lesser horn and superior body of hyoid

skeletal derivatives of pharyngeal arch 3

greater horn and inferior body of hyoid

skeletal derivatives of pharyngeal arches 4 and 6

laryngeal cartilages (epiglottis, thyroid, cricoid, arytenoid, corniculate, cuneiform)

cranial nerve of arch 1

CN V (trigeminal V3)

cranial nerve of arch 2

CN VII (facial)

cranial nerve of arch 3

CN IX (glossopharyngeal)

cranial nerve of arches 4 and 6

CN X (vagus)

muscles derived from arch 1

muscles of mastication

mylohyoid

anterior belly of digastric

tensor tympani

tensor veli palantini

muscles derived from arch 2

muscles of facial expression

stapedius

stylohoid

posterior belly of digastric

muscles derived from arches 4 and 6

most pharyngeal muscles

most palate muscles

all intrinsic laryngeal muscles

cricothyroid (exception)

innervation of arches 4 and 6 muscles

superior laryngeal nerve → cricothyroid

recurrent laryngeal nerve → remaining intrinsic laryngeal muscles

derivatives of pharyngeal pouch 1

auditory (Eustachian) tube

tympanic cavity

mastoid air cells

derivative of pharyngeal pouch 2

palatine tonsils

derivatives of pharyngeal pouch 3

thymus

inferior parathyroid glands

derivatives of pharyngeal pouch

superior parathyroid glands

parafollicular (C) cells of thyroid (via ultimobranchial body)

derivative of pharyngeal groove 1

external acoustic meatus

what happens to pharyngeal grooves 2-4

form cervical sinus, which normally obliterates

derivative of pharyngeal membrane 1

tympanic membrane

pharyngeal arch contributions to middle ear ossicles

arch 1: malleus, incus

arch 2: stapes

which pharyngeal structure contribute to conductive hearing

PA1 and PA2 (ossicles, muscles)

PP1 (middle ear cavity, auditory tube)

PG1 (external acoustic meatus)

PM1 (tympanic membrane)

what is branchial cleft cyst

enclosed epithelial-lined cavity from persistent cleft

what is branchial sinus

opening to either skin or pharynx

what is branchial fistula

tract open at both skin and pharynx

typical location of branchial cleft cysts

anterior to SCM muscle

key features of Pierre Robin syndrome

micrognathia

glossoptosis

cleft palate

otitis media → conductive hearing loss

major features of Treacher Collins syndrome

mandibular and zygomatic hypoplasia

ear malformations (external and middle)

conductive hearing loss

normal intelligence

inheritance of Tracher Collins syndrome

autosomal dominant; can be teratogenic

embryologic cause of DiGeorge syndrome

failure of pharyngeal pouches 3 and 4 to differentiate

key features of DiGeorge syndrome

cardiac defects

thymic hypoplasia → T-cell deficiency

hypocalcemia (decrease PTH)

abnormal facies

cleft palate

22q11 deletion

embryologic origin of thyroid gland

endodermal proliferation at foramen cecum

what is thyroglossal duct

path of thyroid descent from tongue to neck

adult remnant of thyroglassal duct

foramen cecum

classic features of thyroglossal duct cyst

midline neck mass

elevates with swallowing or tongue protrusion

most common location of ectopic thyroid tissue

lingual thyroid (~90%)