head and neck embryology

Question 1

pharyngeal arch

Answer 1

formed by bilateral growth of embryonic tissues in the ventro-lateral region of the head, 5 pairs of pharyngeal arches form in cranial to caudal sequence, are seperated by pharyngeal grooves/ clefts on outside, formation is driven by the migration and proliferation of neural crest cells

Question 2

components of pharyngeal arch

Answer 2

out side covering is ectoderm, inside lining is endoderm, core of each arch is mesenchyme (major component is neural crest cells, the future cartilage and bones, also paraaxial mesoderm, the future skeletal muscles and bring with it their own cranial nerve and blood vessel)

Question 3

pharyngeal pouch

Answer 3

separates pharyngeal arches from the inside (endoderm lined)

Question 4

pharyngeal membrane

Answer 4

where ectoderm and endoderm come together at clefts/grooves

Question 5

Pharyngeal cleft/groove

Answer 5

separates pharyngeal arches from the outside (ectoderm lined)

Question 6

Pharyngeal arch 1 derivatives

Answer 6

Maxillary prominence to Maxillary bone, zygomatic & squamous portions of temporal bone, Mandibular prominence becomes Meckel’s cartilage, mandible, malleus, incus, anterior ligament of the malleus

Question 7

Pharyngeal arch 2 derivatives

Answer 7

Lesser cornu of hyoid, stylohyoid ligament, styloid process, stapes

Question 8

Pharyngeal arch 3 derivatives

Answer 8

Body and greater cornu of hyoid

Question 9

Pharyngeal arch 4 (6) derivatives

Answer 9

thyroid cartilage and cricoid cartilage

Question 10

Pharyngeal arch 1 mesoderm derivatives

Answer 10

Muscles of mastication: temporalis, masseter, mylohyoid, ant belly of diagastric m, tensor tympani, with innervation of the trigeminal nerve

Question 11

Pharyngeal arch 2 mesoderm derivatives

Answer 11

Muscles of facial expression, stylohoid, post belly of digastric m., innervated by facial nerve

Question 12

Pharyngeal arch 3 mesoderm derivatives

Answer 12

Stylopharyngeus, with innervation by glossopharyngeal

Question 13

Pharyngeal arch 4 mesoderm derivatives

Answer 13

Pharyngeal constrictors, soft palate m., laryngeal m., with innervation of vagus nerve

Question 14

pharyngeal pouch 1 derivatives

Answer 14

Tubotympanic recess becomes tympanic cavity, mastoid antrum, auditory tube

Question 15

pharyngeal pouch 2 derivatives

Answer 15

Palatine tonsilar bed, which induces lymphoid tissue invasion and together form the palatine tonsil

Question 16

pharyngeal pouch 3 derivatives

Answer 16

two buds, Ventral bud becomes thymus, Dorsal bud becomes inferior parathyroid

Question 17

pharyngeal pouch 4 (6) derivatives

Answer 17

two buds, Ventral bud becomes ultimopharyngeal body (parafollicular cells in thyroid that produce calcitonin), Dorsal bud becomes superior parathyroid

Question 18

1st pharyngeal membrane

Answer 18

gives rise to the tympanic membrane

Question 19

pharyngeal groove 1 derivatives

Answer 19

external acoustic meatus

Question 20

pharyngeal groove 2-4 derivatives

Answer 20

Coalesce into cervical sinus as arch 2 and 4 expand as folds toward each other and once the folds fuse, the sinus becomes the cervical vesicle. The neck line becomes smooth and cervical vesicle degenerates over time

Question 21

Cervical (branchial) cyst

Answer 21

Persistent cervical vesicle. Presents as asymptomatic swelling on lateral neck, anywhere along the anterior border of sternocleidomastoid

Question 22

Cervical (branchial) sinus

Answer 22

Persistent cervical sinus or any cleft/pouch

Question 23

Cervical (branchial) fistula

Answer 23

Continuous duct between pharynx and neck surface

Question 24

development of the thyroid gland

Answer 24

Endoderm between pharyngeal arch 1 & 2 form a thyroid primordium in the midline and invaginate caudally, As the thyroid primordium grows caudally, it is still open to the pharynx via thyroglossal duct which opens into pharyngeal space at foramen cecum Thyroid primordium continues to grow down below the hyoid bone and takes resident anterior to trachea, caudal to larynx, and matures into thyroid gland. Thyroglossal duct degenerates. Portion of it may become the pyramidal lobe of thyroid. Foramen cecum becomes a remnant (indentation) between anterior & posterior tongue

Question 25

Thyroglossal duct cyst (TDC)

Answer 25

Cystic remnant of thryoglossal duct. Most common mass in the midline of the neck in children. Most commonly present at the level of hyoid bone. May contain ectopic thyroid tissue

Question 26

development of the tongue

Answer 26

1st arch forms Median lingual swelling (tuberculum impar) Lateral lingual swellings à Ant 2/3 of the tongue. 2nd arch forms Copula. 3rd & 4th arches forms Hypopharyngeal eminence à Post 1/3 of the tongue. Arch 1 is mostly covered by ectoderm, thus the lining of ant 2/3 of the tongue derives from ectodermal origin whereas post 1/3 of the tongue (and the rest of the pharyngeal) lining derive from endodermal origin, Skeletal muscles of the tongue derive from occipital somites. Migrate into tongue after 5th week, “pulling in” the motor innervation: Hypoglossal nerve

Question 27

Median sulcus

Answer 27

formed by line of fusion between two lingual swellings

Question 28

terminal sulcus

Answer 28

formed by line of fusion between arch 1 and hypopharyngeal eminence

Question 29

Foramen cecum

Answer 29

the point of attachment of the thyroglossal duct and is formed during the embryological descent of the thyroid gland.

Question 30

Innervation of the Tongue

Answer 30

Anterior 2/3 has Somatosensory – V3 and Special sensory – VII. Posterior 1/3 has Somatosensory – IX & X and Special sensory – IX. Muscles (motor) is XII

Question 31

papillae and taste buds on tongue

Answer 31

include filliform (no taste buds), fungiform, folliate, and circumvallate

Question 32

fungiform

Answer 32

mushroom shaped projections on the tongue. They are found on the upper surface of the tongue, scattered amongst the filiform papillae but are mostly present on the tip and sides of the tongue. They have taste buds

Question 33

filliform

Answer 33

the most numerous of the lingual papillae. Unlike the other kinds of papillae, filiform papillae do not contain taste buds. They cover most of the front two thirds of the tongue’s surface. They appear as very small, conical or cylindrical surface projections,

Question 34

folliate

Answer 34

short vertical folds and are present on each side of the tongue.[2] They are located on the sides at the back of the tongue, just in front of the palatoglossal arch

Question 35

circumvallate

Answer 35

dome-shaped structures on the human tongue that vary in number from eight to twelve. They are situated on the surface of the tongue immediately in front of the foramen cecum and sulcus terminalis, forming a row on either side

Question 36

tastebuds

Answer 36

Multicellular receptor organs in fungiform, filiform & circumvallate papillae, Transmit taste information to CNS via VII & IX, Functional in utero, Fetal swallowing of amniotic fluid changes in response to sweet or bitter substances

Question 37

face formation

Answer 37

Week4: Face begins as five facial primordia around stomodeum, including Frontonasal prominence (FNP), Paired maxillary prominences (MxP), Paired mandibular prominences (MdP)

Question 38

nasal placodes

Answer 38

(ectodermal thickening) form on FNP, Underlying mesenchyme around nasal placodes proliferate, creating elevations around the placodes Nasal placodes “sink in” & become nasal pits, then dilate to become nasal sacs. Elevated regions around the nasal pit are called nasal prominences, which are divided into medial and lateral portions. MxPs grow & enlarge, “pushing” nasal prominences toward midline of the face. Medial nasal prominences fuse (Week 6-10), giving rise to Bridge of the nose and Intermaxillary segment

Question 39

intermaxillary segment

Answer 39

form Portion of the upper lip (philtrum), Upper jaw with 4 incisors, Primary palate. MxPs fuse with the intermaxillary segment. Ventral region à smooth upper lip. Dorsal region à fusion of primary and secondary palate

Question 40

lateral nasal prominences

Answer 40

give rise to the alae of the nose and fuse with MxP, At the site of fusion, ectoderm thickens into a cord then “sinks” into underlying mesenchyme which canalizes to become the nasolacrimal duct

Question 41

development of nasal cavity

Answer 41

Two nasal pits form nasal sacs. Nasal sacs fuse in the midline, forming a single nasal cavity separated from oral cavity by a thin oronasal membrane. Oronasal membrane ruptures dorsal to primary palate to become oral and nasal cavity becomes continuous. Formation of secondary palate separates nasal cavity from oral cavity. Nasal septum separates right and left nasal cavities. Nasal conchae develop from the lateral walls of the nasal cavities. Cranial ectoderm in the nasal cavity differentiate and specialize to become Olfactory epithelium

Question 42

palate

Answer 42

separates nasal cavity from oral cavity, preventing aspiration of food. Anatomical division include Hard palate: Anterior, bony portion, comprises the majority of the palate and Soft palate: Small, fleshy, posterior portion, terminating in the uvula. embryonic divsion includes primary and secondary palate

Question 43

primary palate

Answer 43

Derives from intermaxillary segment (fused medial nasal prominences). Gives rise to anterior, triangular portion of the hard palate

Question 44

Secondary palate

Answer 44

Derives from the fusion of palatine shelves that grow from the MxPs. Gives rise to the majority of hard palate and all of soft palate

Question 45

Development of the secondary palate

Answer 45

Palatal processes (palatine shelves) form from MxP internally and Grow caudally on either side of the developing tongue. At Week9, growth of mandible “drops” tongue, allowing palatine shelves to swing up and fuse with: each other in the midline and primary palate anteriorly, formation is complete at 12 weeks

Question 46

tooth development

Answer 46

includes buds stage, cap stage, and bell stage, Both baby/deciduous teeth, and adult/permanent/successional teeth are generated during fetal development, although their development is staggered. Much of the growth of the maxilla and mandible during later gestation and postnatally is to accommodate growth of the second set of tooth buds. Tooth development is key to normal jaw growth.

Question 47

bud stage

Answer 47

first stage, The dental lamina forms in the epithelium of the mandible and maxilla. The ectodermal epithelium then invaginates to form dental buds - 10 per jaw (8 wks).

Question 48

cap stage

Answer 48

second stage, The bud epithelium then invaginates, forming a cap around condensing dental papilla mesenchyme, which is derived from neural crest (10 wks).

Question 49

bell stage

Answer 49

neural crest mesenchyme cells become odontoblasts, destined to produce dentin, and outer epithelial/ectodermal cells differentiate as ameloblasts, which will produce enamel (3 months +). Ameloblasts are sloughed off when the teeth erupt postnatally. Baby/deciduous teeth erupt in a typical sequence.