- What are the basic components of a typical pharyngeal arch
- A Pharyngeal arch artery
- A Pharyngeal cartilage
- A Muscular component
- Sensory and motor nerves
- List the derivatives of branchial arches
- First (mandibular)
- Nerve – CN V2 and V3
- Muscles – Muscles of mastication, Mylohyoid, Anterior belly of digastric, Tensor tympani, Tensor Veli palatini
- Skeleton – Malleus, Incus, premaxilla, Maxilla, Zygomatic bone, Meckel’s cartilage, Mandible, Anterior ligament of malleus, Sphenomandibular ligamnet
- Second (Hyoid)
- Nerve – CN VII
- Muscles – Facial expression, posterior belly of digastric, stylohyoid, stapedius
- Skeleton – stapes, styloid process, stylohyoid ligament, lesser horn and upPer portion of body of hyoid bone
- Third
- Nerve – CN IX
- Muscle – stylopharyngeus
- Skeleton – Greater horn and lower portion of hyoid bone
- Fourth & sixth
- Nerve – CN X
- Muscles – cricothyroid, levator palatini, pharyngeal constrictors and intrinsic laryngeal muscles
- Skeleton – laryngeal cartilages
- First (mandibular)
- List the derivatives of the branchial pouches
- I – Tympanic cavity (middle ear) and eustachian tube
- II – Palatine tonsils and tonsillar fossa
- III – inferior parathyroid and thymus
- IV – superior parathyroid and ultimobranchial body
- List the derivatives of the branchial arch arteries
- I – Maxillary artery
- II – Hyoid and stapedial arteries
- III – common carotid and proximal internal carotid
- IV – proximal right subclavian artery and aortic arch
- VI – pulmonary artery and ductus arteriosus
- Briefly describe the development of the thyroid gland
- Forms as a thickening on the floor of the primordial pharynx between the tuberculum impa and copula linguae under the influence of FGF signaling
- Floor thickens to form the thyroid primordium
- The developing gland descends ventral to the developing hyoid and larynx as the tongue grows via the thyroglossal duct
- The gland remains connected to the tongue via the thyroglossal duct
- Divides into right and left lobes connected at the isthmus
- Thyroglossal duct degenerates and the proximal opening persists as foramen cecum of the tongue
- The ultimobranchial body forms from the ventral wing of the 4th pouch and joins the thyroid in its descent
- The Ultimobranchial body forms C – cells
- State 5 associated congenital anomalies associated with the development of the thyroid gland (with respective embryological basis)
- Congenital hypothyroidism Mutations in TSHR and (Thyroid Transcription Factors) TTFs
- Thyroglossal duct cyst Remnant of the thyroglossal duct
- Thyroglossal duct sinus Communication of the thyroglossal duct cyst with the skin, usually in the median plane anterior to laryngeal cartilage
- Ectopic thyroid gland Ectopic thyroid tissue located along the course of the thyroglossal duct i.e. Lingual thyroid – intralingual and sublingual
- Agenesis/ Hemigenesis of the thyroid gland Absence of the thyroid gland/ left lobe possibly due to TSHR mutations
- Briefly describe the development of the tongue
- Medial lingual swelling appears rostral to foramen cecum
- Lateral lingual swellings develop on each side of the medial lingual swellings
- Lateral lingual swellings merge to form the anterior 2/3 of the tongue – line of fusion lingual septum and midline groove
- Caudal to foramen cecum, copula swelling develops from second pharyngeal arch
- Hypopharyngeal eminence develops from pharyngeal arches 3 and 4
- Hypopharyngeal eminence overgrows copula forming posterior 1/3 of the tongue – line of fusion sulcus terminalis
- State 5 associated congenital anomaliesassociated with the development of the tongue (with embryological basis)
- Congenital lingual cyst – thyroglossal duct remnant
- Congenital lingual fistula – persistent thyroglossal duct
- Ankyloglossia – An abnormal short frenulum that anchors the tongue to the oral floor
- Macroglossia – generalized hypertrophy of the developing tongue (Down or Beckwith-Wiedemann syndrome)
- Microglossia – A small tongue associated with micrognathia and limb defects (Hanharth syndrome)
- Glossoschisis (Bifid/cleft tongue) – incomplete fusion of lateral lingual swellings leads to deep fissure in the midline
- What is the embryological basis of the following congenital anomalies: Unilateral cleft lip and palate, oblique facial cleft, bilateral cleft lip, midline cleft lip, isolated cleft palate
- Unilateral cleft lip and palate Failed fusion of ipsilateral maxillary prominence with fused medial nasal prominence
- Oblique facial cleft Failed fusion of maxillary prominence with its corresponding lateral nasal prominence
- Bilateral cleft lip Failed fusion of maxillary prominences with medial nasal prominences
- Midline cleft lip Failed fusion of medial nasal prominences to form the median palatal processs
- Isolated cleft palate Nonfusion of the palatine shelves
