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Questions and Answers
What is the initiating factor for dental development around week 7?
What is the initiating factor for dental development around week 7?
During which stage do the dental buds proliferate as oval masses?
During which stage do the dental buds proliferate as oval masses?
What is the function of the outer dental epithelium during the Cap Stage?
What is the function of the outer dental epithelium during the Cap Stage?
Which cranial nerve is responsible for sensory innervation to the root of the tongue?
Which cranial nerve is responsible for sensory innervation to the root of the tongue?
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What structure begins to take final shape during the Bell Stage?
What structure begins to take final shape during the Bell Stage?
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What is the term for the structure that produces future tooth enamel within the cap?
What is the term for the structure that produces future tooth enamel within the cap?
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What structure marks the fusion of the 1st pharyngeal arch tongue with the pharyngeal arches 2–4?
What structure marks the fusion of the 1st pharyngeal arch tongue with the pharyngeal arches 2–4?
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What occurs around week 9 during the Cap Stage?
What occurs around week 9 during the Cap Stage?
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Where does the thyroid gland develop from during embryogenesis?
Where does the thyroid gland develop from during embryogenesis?
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What is the final developmental position of the thyroid gland typically reached around week 7?
What is the final developmental position of the thyroid gland typically reached around week 7?
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What forms as a condensation of neural crest mesenchyme within the Cap Stage?
What forms as a condensation of neural crest mesenchyme within the Cap Stage?
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Which cells transform into odontoblasts during the Bell Stage?
Which cells transform into odontoblasts during the Bell Stage?
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Which structure primarily gives rise to the philtrum and upper lip?
Which structure primarily gives rise to the philtrum and upper lip?
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What surrounds the base of the cap structure during the Cap Stage?
What surrounds the base of the cap structure during the Cap Stage?
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What is the initial developmental stage of the secondary palate?
What is the initial developmental stage of the secondary palate?
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What structure typically obliterates during the development of the thyroid gland?
What structure typically obliterates during the development of the thyroid gland?
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What is the result of the expansion of enamel and dentin into the mesenchyme?
What is the result of the expansion of enamel and dentin into the mesenchyme?
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What is the role of C Cells in the thyroid gland?
What is the role of C Cells in the thyroid gland?
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Which of the following components originates from endoderm during thyroid development?
Which of the following components originates from endoderm during thyroid development?
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What anatomical feature marks the fusion point of the primary and secondary palates?
What anatomical feature marks the fusion point of the primary and secondary palates?
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What role do cementoblasts play in tooth development?
What role do cementoblasts play in tooth development?
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What is the approximate time frame from root lengthening to tooth emergence?
What is the approximate time frame from root lengthening to tooth emergence?
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How do the nasal pits develop during facial formation?
How do the nasal pits develop during facial formation?
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What significance do the paranasal sinuses have in facial development?
What significance do the paranasal sinuses have in facial development?
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What structure do the medial nasal prominences eventually form?
What structure do the medial nasal prominences eventually form?
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What process connects the oral and nasal cavities during development?
What process connects the oral and nasal cavities during development?
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Which feature is a result of the lateral nasal prominences?
Which feature is a result of the lateral nasal prominences?
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What initiates the production of permanent tooth buds?
What initiates the production of permanent tooth buds?
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What helps anchor the tooth in addition to cementum?
What helps anchor the tooth in addition to cementum?
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Which part of the nose is formed from the fusion of medial nasal prominences?
Which part of the nose is formed from the fusion of medial nasal prominences?
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What is the main structure that forms the forehead and bridge of the nose during facial development?
What is the main structure that forms the forehead and bridge of the nose during facial development?
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At what week does the orofacial development begin?
At what week does the orofacial development begin?
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Which structure is responsible for forming the internal ear during development?
Which structure is responsible for forming the internal ear during development?
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What do the lateral swellings and tuberculum impar contribute to during tongue development?
What do the lateral swellings and tuberculum impar contribute to during tongue development?
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Which two structures invaginate to form the nasal pits?
Which two structures invaginate to form the nasal pits?
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What is the hypobranchial eminence a swelling from?
What is the hypobranchial eminence a swelling from?
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What does the mandibular prominence primarily develop into?
What does the mandibular prominence primarily develop into?
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Which structure is located anteriorly and laterally to the frontonasal prominence?
Which structure is located anteriorly and laterally to the frontonasal prominence?
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What develops from the medial swelling of the 1st pharyngeal arch?
What develops from the medial swelling of the 1st pharyngeal arch?
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Which structure primarily becomes the lateral upper lip and cheeks?
Which structure primarily becomes the lateral upper lip and cheeks?
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Study Notes
Facial Development
- Facial development initiates around week 4, centered around the stomodeum (primordial oral cavity).
- Placodes, ectodermal thickenings, form specialized structures.
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Key structures during facial development:
- Stomodeum: Primordial oral cavity.
- Frontonasal prominence: Located above the stomodeum, forms the forehead and bridge of the nose.
- Lens placodes: Lateral to the frontonasal prominence, migrate medially during development to become eyes and associated tissues.
- Otic placodes: Form the internal ear structures.
- Nasal placodes: Anterolateral to the frontonasal prominence, invaginate to form nasal pits, creating two nasal prominences (lateral and medial nasal prominences).
- Maxillary prominences: Lateral to the stomodeum, develop into the lateral upper lip and cheeks; derived from the first pharyngeal arch.
- Mandibular prominences: Below the stomodeum, develop into the lower lip; derived from the first pharyngeal arch.
Tongue Development
- Develops around week 4.
- Composed of 5 structures:
- Two lateral swellings: From the first pharyngeal arch.
- Tuberculum impar: Medial swelling from the first pharyngeal arch.
- Hypobranchial eminence: Medial swelling from mesoderm of pharyngeal arches 2-4.
- Epiglottal medial swelling: From the fourth pharyngeal arch.
- The lateral swellings and tuberculum impar grow into the anterior 2/3 of the tongue.
- The anterior 2/3 of the tongue is innervated by the trigeminal nerve (mandibular branch CN V3) due to its origin from the first pharyngeal arch.
- The hypobranchial eminence becomes the root of the tongue.
- The root of the tongue is innervated by the glossopharyngeal nerve (CN IX) and a small portion by the vagus nerve (CN X), reflecting its development from the third and fourth pharyngeal arches, respectively.
- The sulcus terminalis marks the fusion of the first pharyngeal arch tongue with the pharyngeal arch 2-4 tongue.
Thyroid Gland Development
- Closely linked to tongue development.
- Forms from epithelial proliferation between the tuberculum impar and copula, in a depression called the foramen cecum.
- Descends anteriorly to the developing pharynx, hyoid, and laryngeal cartilages, reaching its final position around week 7.
- Remains connected to the tongue via the foramen cecum and thyroglossal duct, which typically obliterates during development.
- Becomes functional around the third month.
- Functional components:
- Follicular cells: Produce colloid, the source of thyroxine and triiodothyronine, deriving from endoderm.
- C cells: Produce calcitonin for controlling calcium metabolism, deriving from the ultimobranchial body of the fourth pharyngeal arch.
Palate Development
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Primary palate:
- Triangular segment of the anterior palate.
- Derived from the intermaxillary segment, a structure formed from the merging of the maxillary prominences and medial nasal prominences.
- Forms the philtrum, upper lip, and incisors.
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Secondary palate:
- Formed from the palatine shelves, medial outgrowths of the maxillary prominences that emerge around week 6.
- Initially project below the tongue, but eventually merge to form the roof of the oral cavity.
- Fuse with the primary palate, with the incisive foramen marking the fusion point.
- The nasal septum fuses with the superior surface of the primary and secondary palates.
- Forms the bony palate posterior to the incisive foramen and the soft palate.
Tooth Development
- Result of interaction between oral epithelium and deeper neural crest-derived mesenchyme.
- Face shape is partially dictated by the expansion of the maxilla and mandible to accommodate teeth.
- Initiation begins around week 7 through signaling mechanisms between epithelium and mesenchyme.
- Dental lamina: Forms around week 6-7, a c-shaped invagination into the mesenchyme. A dental placode develops inside each dental lamina.
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Dental bud stage: (around week 8)
- Dental placodes proliferate as oval masses in the mesenchyme. A basement membrane separates the bud from the mesenchyme. Each jaw develops 10 dental buds.
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Cap stage: (around week 9)
- Deep surface of the dental bud becomes concave (cap), surrounding a dental papilla (condensation of neural crest mesenchyme, future dentin and pulp cavity).
- Outer edge of the curved arms of the cap becomes outer dental epithelium; inner edges become inner dental epithelium. Outer dental epithelium protects and nourishes internal enamel organ; inner will become enamel-secreting ameloblasts in the Bell stage.
- The center of the inner dental epithelium forms the enamel knot, a signaling center guiding tooth development.
- Enamel organ, within the cap, fills with stellate reticulum, which will produce tooth enamel.
- Dental sac, a mesenchymal structure surrounding the base of the cap, will develop into the periodontium.
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Bell stage: (around week 11)
- Concavity of the deep surface deepens.
- Crown begins to take its final shape.
- Dental papilla closest to the inner dental epithelium become odontoblasts, which create dentin. The remainder becomes the pulp of the tooth.
- Enamel and dentin begin to form below the apex of the inner dental epithelium.
- As enamel and dentin layers expand, they penetrate into the mesenchyme as the epithelial root sheath.
- Further dentin production from the crown extends down, narrowing the pulp chamber and forming a canal for vessels and nerves.
- Mesenchyme adjacent to the dentin at the root differentiates into cementoblasts, producing cementum to hold the tooth in place.
- Adjacent to the cementum, mesenchyme produces the periodontal ligament, further anchoring the tooth.
- Lengthening of the root pushes the tooth to the surface around 6-24 months after birth.
- Permanent tooth buds form around the third month of development, but don't become active until around 6 years of age. These teeth will replace the deciduous teeth.
Nose and Nasal Cavity Development
- Nasal placodes sink into the face to form nasal pits around week 5.
- An oronasal membrane initially separates the developing nasal cavity from the oral cavity, which disintegrates to connect the two cavities. The palate pushes this connection posteriorly, leading to the development of the choanae.
- Two crescent structures form around each nasal pit, the medial and lateral nasal prominences.
- Lateral nasal prominences: Develop into the ala of the nose.
- Medial nasal prominences: Fuse to form the medial part of the nose from the root to the tip, as well as the philtrum and medial upper lip. They fuse with the maxillary prominences to complete the upper lip.
- Form the intermaxillary segment and the nasal septum.
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Paranasal sinuses:
- Air-filled expansions from the lateral nasal walls into adjacent bones (e.g., maxilla).
- Some appear during the fetal period, and all continue to develop until puberty.
- Contribute to the shape of the face.
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Description
This quiz focuses on the key structures involved in facial development, highlighting the role of various prominences and placodes around week 4 of embryonic development. Test your knowledge on how these structures contribute to the formation of important facial features such as the mouth, nose, and eyes.
