Development (L5-L9) Flashcards
Name the primary germ layers
- Ectoderm
- Mesoderm
- Endoderm
- Neural Crest/Ecto-mesenchyme
Where does ectoderm come from and what does it develop into?
From epiblast; develop into: skin, neural tube etc.
Where does mesoderm come from?
From the migratory cells of the epiblast layer
Where does endoderm come from
from the hypoblast layer
When do pharyngeal arches appear?
in the 4th-5th week
What lines the outer surface of the pharyngeal arches?
Ectoderm
What lines the inner surface of the pharyngeal arches?
Endoderm
What does each pharyngeal arch contain?
An artery, nerve, cartilage, muscles
What is the 1st arch?
Mandibular arch
What cartilage is in the 1st arch?
Meckel’s cartilage
What does meckel’s cartilage form
- Bones: Incus & Malleus
- Ligaments: Sphenomandibular & Sphenomalleolar
What does the 1st arch give rise to?
- body of tongue
- muscles of mastication (temporalis, masseter, pterygoid, mylohyoid, anterior body of digastric)
Which nerve supplies the mandibular arch?
CN V (Trigeminal)
Which arteries supply the 1st/ mandibular arch?
Carotid / Maxillary artery
Name a disease caused by the degeneration of the mandibular arch
Treacher-Collin’s syndrome
What is the 2nd arch called?
Hyoid arch
Which cartilage is in the 2nd arch
Reichert’s cartilage
What forms from the Reichert’s cartilage?
Stapes, Lesser horn and superior hyoid body, styloid process, stylohyoid ligament
Which muscles form from the hyoid arch?
Muscles of facial expression and posterior belly of digastric muscle
Which nerve supplies the hyoid arch?
Facial nerve (CN VII)
What does the 2nd arch give rise to?
- Thyroid gland
- Tonsil
Which nerve supplies the 3rd arch?
CN IX (Glossopharyngeal nerve)
Which muscle does the 3rd arch supply
Stylopharyngeus muscle
What does the 3rd arch form?
- greater horn of hyoid
- inferior hyoid body
- root of the tongue
What cartilage does the 4th arch give rise to?
Thyroid cartilage
What structures does the 4th arch give rise to?
Pharynx & Epiglottis
Which nerve supplies the 4th arch?
CN X (Vagus) - superior laryngeal branch
Which muscles do the 4th arch form?
Pharyngeal constrictor and muscles of the soft palate
Which nerve supplies the 6th arch?
CN X (Vagus) - Inferior laryngeal nerve
What does the 1st cleft/groove give rise to?
External auditory meatus; Ear drum
What does the 1st pouch give?
- Eustachian tube
- Middle ear cavity
- Tympanic membrane
- Ventral part obliterated by tongue
What does the 2nd pouch give?
Tonsillar fossa & Ventral part obliterated by tongue
What does the 3rd pouch give?
Inferior parathyroid gland & Thymus
What does the 4th pouch give?
Superior parathyroid gland (will fuse with the inferior one)
Also becomes the parafollicular (C cells) associated with the thyroid gland that produces calcitonin
Name the 5 facial processes
Frontonasal process, paired maxillary process, paired mandibular process
When does development of the face start?
At 4 weeks
What is “fusion” VS true fusion?
“Fusion” involves the fusion of prominences by elimination of furrow whereas true fusion involves the fusion of separate processes
Name an example of “fusion”
Between the medial nasal prominence
Give an example where true fusion takes place
Between the medial nasal prominence and the maxillary process
Which facial structure does the frontonasal prominence contribute to?
Forehead, bridge of nose
Which facial structure does the medial nasal prominence contribute to?
Philtrum of lip, crest and tip of the nose
Which facial structure does the lateral nasal prominence contribute to?
Alae of nose
Which facial structure does the maxillary prominence contribute to?
Cheeks, lateral upper lip
Which facial structure does the mandibular prominence contribute to?
Lower lip
What do mesenchymal cells give?
Osteoblasts and chondroblasts
When does ossification of the mandible begin?
Week 6-7
When does ossification of the maxilla begin?
Week 8
When does ossification of the palate and nasal capsule begin?
Week 8
What is the primary palate derived from?
Medial nasal prominences (part of frontonasal prominence)
What is the secondary palate formation?
It is the contact of lateral palatal shelves at the midline.
What is the function of the secondary palate?
It separates the nasal airway and the oral cavity
State the functions of the secondary palate
- Mastication (Bolus formation)
- Sensation of taste and texture
- Speech
Describe the growth of the palatal shelves
Initially, the palatal shelves develop medially and downwards. At week 8, they then rapidly elevate (flip upwards into a horizontal orientation) and grow towards each other.
Name a source of extrinsic force involved in palatal shelve elevation
Tongue - withdrawal of the tongue due to head lifting from cardiac plate; Meckel’s cartilage growth in the 1st pharyngeal arch and increased height of nasal cavity
Describe the intrinsic shelf force w.r.t palatal shelve elevation
- A turgor pressure is generated by hydration of the extracellular matrix by hyaluronan, a glycosaminoglycan (GAG).
- Proliferation of mesenchymal cells result in shortening via contractile microfilaments produces the force
- Partly directed by Type I collagen which provides strength and is very flexible
Name 3 sources of palatal fusion problems
- Lack of matrix factors (lack of expression of HA by HA synthase 1/2/3)
- Failure to fuse (completely/incompletely) - cleft palate
- Epithelial remnants - epithelial cell rests/ cystic potential
What allows the fusion of palatal shelves with just itself and not with other epithelial?
Specific sticky surface glycoprotein
How does the midline disintegrate during fusion of the palatal shelves?
Epithelial-mesenchymal transition - switching of epithelial cells to mesenchymal
What precedes the mandible?
Meckel’s cartilage
What does Meckel’s cartilage precede?
Mandible
What role does Meckel’s cartilage play in mandible formation?
It serves as a template for the formation of the mandible (bone formation follows the line of cartilage)
What structure(s) does the posterior extremity of Meckel’s cartilage give?
Malleus of inner ear & Sphenomalleolar ligament
Where is the position of the Meckel’s cartilage?
It extends from the otic capsule (bony capsule of developing inner ear) to a midline symphysis
Where is the primary ossification site of the mandible?
Between the incisive and mental nerve
Is there a change in ossification type of mandible from primary to secondary cartilage sites?
Yes, from intramembranous ossification to endochondral ossification
Name some growth factors involved in the formation of the mandible
VEGF (vascular endothelial growth factor)
TGFB (transforming growth factor-beta)
BMPs
What forms where the mandibular bone envelopes the inferior alveolar nerve?
Mental foramen
Name the 3 mandibular secondary cartilage
- Symphyseal
- Coronoid
- Condylar
State when the symphyseal cartilage appear and disappear
Appears at 16 weeks
Disappears at 1st year after birth
State when the coronoid cartilage appear and disappear
Appears at 14-16 weeks
Disappears before birth
State when the condylar cartilage appear and disappear
Appears at 10-12 weeks
Disappears at about 20 years of age
Function of the condylar cartilage
Produces cartilage when jaw starts to work; allowing endochondral sites formation
Function of the symphyseal cartilage
Allows for fusion of the 2 mandible when it disappears
How is the primary cartilage different from the secondary cartilage?
- Primary cartilage uses intramembranous ossification whereas secondary cartilage uses endochondral ossification
- Primary cartilage has hyaline cartilage; Secondary cartilage has fibrocartilage
- Primary cartilage uses interstitial growth; Secondary cartilage uses appositional growth
List 3 developmental abnormalities of the mandible
- Agnathia - no mandible
- Micrognathia - very small mandible
- Macrognathia - very large mandible
What results in agnathia and micrognathia?
Lack of ectomesenchyme in the mandibular arch
What disorder is macrognathia associated with?
Genetic; pituitary disorders - e.g. acromegaly
When does development of the tongue start?
at 4 weeks iul
Which pharyngeal arch is involved in the development of the tongue?
Arch 1, 3, 4
Which part of the tongue does pharyngeal arch 1 form
anterior 2/3rds of the tongue
Which part of the tongues does pharyngeal arch 3 form?
posterior 1/3rd of the tongue
What does pharyngeal arch 4 form in relation to the tongue
Tongue muscles
What is the anterior 2/3rd and posterior 1/3rd of the tongue separated by?
Sulcus terminalis
What does the first pharyngeal arch contain in relation to the tongue?
2 lingual swelling &
1 tuberculum impar (medial swelling)
What does the third pharyngeal arch contain in relation to the development of the tongue?
Hypobranchial eminence
What causes the detachment of the anterior 2/3rd of the tongue?
Ectoderm grows between anterior 2/3rd of the tongue and the underlying arch. Ectoderm degenerates except in the midline, resulting in separation of tongue except for the midline frenulum.
Where does the anterior 2/3rd of the tongue come from and name its general sensory sensation innervation
Pharyngeal arch 1;
CN V
Where does the posterior 1/3rd of the tongue come from and name its general sensory sensation innervation
Pharyngeal arch 3;
CN IX
Name the 3 types of tongue development abnormalities that could occur
- Failure of fusion
- Imperfect detachment - ankyloglossia
- Growth disorders
What growth disorders of the tongue can there be?
- Aglossia
- Microglossia - small tongue
- Macroglossia - large tongue
Which pharyngeal arch does the thyroid gland develop from?
Arch 2
What is the development of the thyroid gland associated with?
Tongue development
What follows the formation of the thyroid tissue?
Disintegration of the thyroglossal duct
Name 3 abnormalities of thyroid development
- Ectopic thyroid gland
- Persistent thyroglossal duct
- Pathological changes to remnants of the thyroglossal duct (Thyroglossal cyst / Thyroglossal fistula)
