[EMBRYOLOGY] Chapter 17 Head and Neck

"Pharyngeal arches"

"Six paired bars of mesenchyme (covered by ectoderm/endoderm) appearing in weeks 4-5, each with its own cartilage, muscle, nerve, and artery; formerly called branchial arches."

"Meckel cartilage"

"Cartilage of the first pharyngeal arch's mandibular process; mostly disappears except its dorsal end, which forms the malleus and incus."

"Reichert cartilage"

"Cartilage of the second (hyoid) pharyngeal arch; forms the stapes, styloid process, stylohyoid ligament, and lesser horn/upper hyoid body."

"Trigeminal nerve (V)"

"Nerve of the first pharyngeal arch; supplies muscles of mastication and sensation to the face via ophthalmic, maxillary, and mandibular branches."

"Facial nerve (VII)"

"Nerve of the second pharyngeal arch; supplies muscles of facial expression, stapedius, stylohyoid, and posterior digastric."

"Glossopharyngeal nerve (IX)"

"Nerve of the third pharyngeal arch; supplies the stylopharyngeus muscle and general/taste sensation to the posterior tongue."

"Vagus nerve (X)"

"Nerve of the fourth (superior laryngeal branch) and sixth (recurrent laryngeal branch) pharyngeal arches; supplies laryngeal/pharyngeal muscles."

"Pharyngeal pouches"

"Four (plus one rudimentary) paired endodermal outpocketings of the pharynx that give rise to the middle ear, tonsils, thymus, and parathyroid glands."

"Tubotympanic recess"

"Derivative of the first pharyngeal pouch; forms the middle ear cavity distally and the auditory (eustachian) tube proximally."

"Palatine tonsils"

"Derivative of the second pharyngeal pouch, formed by epithelial buds invaded by lymphatic tissue."

"Inferior parathyroid gland"

"Derived from the dorsal region of the THIRD pharyngeal pouch; ends up inferior because it is dragged down by the migrating thymus."

"Thymus"

"Derived from the ventral region of the third pharyngeal pouch; migrates caudally and medially into the anterior thorax."

"Superior parathyroid gland"

"Derived from the dorsal region of the FOURTH pharyngeal pouch."

"Ultimobranchial body"

"Derivative of the ventral fourth pharyngeal pouch; incorporated into the thyroid gland and gives rise to parafollicular (C) cells."

"Parafollicular (C) cells"

"Calcitonin-secreting cells of the thyroid, derived from the ultimobranchial body (fourth pharyngeal pouch)."

"Cervical sinus"

"Temporary space formed when the second pharyngeal arch overgrows and buries the second, third, and fourth pharyngeal clefts; normally obliterates."

"Branchial (lateral cervical) fistula"

"Persistent cervical sinus remnant opening onto the neck surface, anterior to the sternocleidomastoid muscle."

"Treacher Collins syndrome"

"Mandibulofacial dysostosis from TCOF1 mutations causing neural crest apoptosis; features maxillary/mandibular/zygomatic hypoplasia, cleft palate, and ear defects with conductive hearing loss."

"Robin sequence"

"Triad of micrognathia, cleft palate, and glossoptosis (posteriorly placed tongue); occurs in ~1/8,500 births."

"22q11.2 deletion syndrome"

"Most common human deletion syndrome; includes DiGeorge and velocardiofacial syndromes; linked to TBX1; causes cardiac, thymic, and parathyroid defects via shared neural crest origin."

"Hemifacial microsomia (Goldenhar syndrome)"

"Craniofacial spectrum disorder with small maxillary/temporal/zygomatic bones, ear and eye defects, and vertebral anomalies; often asymmetric."

"Tuberculum impar"

"Median swelling of the first pharyngeal arch that contributes to formation of the tongue; overgrown by the lateral lingual swellings."

"Copula (hypobranchial eminence)"

"Median tongue swelling formed by mesoderm of the 2nd, 3rd, and part of the 4th pharyngeal arches; contributes to the tongue root."

"Terminal sulcus"

"V-shaped groove marking the boundary between the body (anterior 2/3) and root (posterior 1/3) of the tongue."

"Foramen cecum"

"Midline pit on the tongue marking the site of origin of the thyroid gland."

"Thyroglossal duct"

"Transient canal connecting the descending thyroid gland to the tongue; normally disappears, but can persist as a thyroglossal cyst."

"Frontonasal prominence"

"Unpaired facial prominence forming the forehead, bridge of the nose, and giving rise to the medial/lateral nasal prominences."

"Medial nasal prominences"

"Paired prominences that fuse with the maxillary prominences to form the upper lip, plus the crest and tip of the nose."

"Lateral nasal prominences"

"Paired prominences forming the alae (sides) of the nose; do NOT contribute to the upper lip."

"Intermaxillary segment"

"Structure formed by deep fusion of the medial nasal prominences; forms the philtrum, four incisor teeth, and primary palate."

"Primary palate"

"Triangular palate segment formed by the palatal component of the intermaxillary segment."

"Secondary (definitive) palate"

"Palate formed by fusion of the palatine shelves (from the maxillary prominences) in week 7."

"Incisive foramen"

"Midline landmark separating the primary and secondary palate; used to classify facial clefts as anterior or posterior."

"Cleft lip"

"Anterior to the incisive foramen; caused by failure of fusion between the maxillary and medial nasal prominences."

"Cleft (secondary) palate"

"Posterior to the incisive foramen; caused by failure of the palatine shelves to fuse."

"Van der Woude syndrome"

"Most common cleft lip/palate syndrome; caused by IRF6 mutations; 88% of affected infants have lower lip pits."

"Holoprosencephaly"

"Severe midline brain/face defect with fused lateral ventricles and synophthalmia, from extensive medial nasal prominence tissue loss (SHH mutation, teratogen exposure, or cholesterol synthesis defects)."