Case 19- Embryology Flashcards
Head and Neck- what does the pharyngeal surface ectoderm give rise to
Contributes to the development of the ear and palate
Head and Neck- what does the pharyngeal (lateral plate) mesoderm give rise to
Gives rise to skeletal structures of the head and neck, to the tongue and forms the pharyngeal arch arteries. From the Somatic mesoderm
Head and neck- what does the pharyngeal endoderm give rise to
Contributes to the development of the pharyngeal organs including the thymus
Head and Neck- What does the neural crest ectoderm give rise
Contributes to the bones of the face and jaw (frontal, sphenoid and temporal bone), to the cranial nerves, and to the remodelling of pharyngeal arteries. Face, jaw, neck and palate
Head and Neck- what does the Paraxial mesoderm give rise
Contributes to the bones of the posterior skull (Parietal and Occipital bone)
What does the pharyngeal arches give rise to
Maxilla, Mandible, bones of middle ear, muscles of mastication, maxillary artery, trigeminal nerve, styloid process, muscles of facial expression, facial nerve, hyoid bone
What do the pharyngeal clefts give rise to
External auditory meatus
What do the pharyngeal membranes give rise to
Tympanic membrane
What do the Pharyngeal pouches form
Tympanic cavity and auditory tube, palatine pouch, inferior parathyroid gland and thymus, superior parathyroid gland
Pharyngeal arches
1) External structures in the embryonic neck region and appear from week 4 of development
2) There are five pharyngeal arches (1,2,3,4 and 6) arch 5 is transient and does not form any adult structures.
Core of the pharyngeal arch
The central core of each pharyngeal arch consists of mesoderm and neural crest. The arch core contains a skeletal element the central rod (give rise to craniofacial bones and cartilages), a neural element (give rise to cranial nerves) and a vascular element (give rise to pharyngeal arch arteries). Next to the Central skeletal rod (cartilage surrounded by muscle) is the Pharyngeal arch artery and a Cranial nerve which is made from neural crest cells. Each nerve in the central arch is a different cranial nerve.
Pharyngeal cleft
The external recesses between each pharyngeal arch- consists of ectoderm
Pharyngeal pouch
Internally, the endoderm lined corresponding recesses
Skeletal structures formed from the different pharyngeal arches
- 1st (Meckel’s cartilage)- Maxillary and Mandibular bone, Mallleus and Incus
- 2nd- Stapes, Styloid process, Stylohyoid ligament, lesser horn of hyoid bone
- 3rd- Hyoid bone
- 4th- Thyroid cartilage
- 6th- Cricoid cartilage
Motor innervation from the pharyngeal arches
- 1st arch- Trigeminal nerve (V), muscles of mastication, gives rise to Ophthalmic, Maxillary and Mandibular branches
- 2nd arch- Facial nerve (VII), muscles of facial expression
- 3rd arch- Glossopharyngeal nerve (IX), controls the Stylopharyngeus muscle which controls swallowing
- 4th arch- Superior laryngeal branch of the Vagus nerve (X), controls the muscles of the pharynx and soft palate
- 6th arch- Recurrent laryngeal branch of the Vagus nerve (X) which controls the muscle of the larynx
When are the pharyngeal arch arteries remodelled into adult vessels
Occurs from 28 to 44 days of development. The neural crest cells migrate in
What does the first pharyngeal cleft and membrane go on to form
The first pharyngeal cleft goes on to form the external auditory meatus
The first pharyngeal membrane forms the tympanic membrane
What do the different pharyngeal pouches go on to form
- 1st pharyngeal pouch forms the tympanic cavity and auditory tube
- 2nd pharyngeal pouch forms the Palatine tonsil
- 3rd pharyngeal pouch forms the inferior Parathyroid gland and Thymus
- 4th pharyngeal pouch forms the Superior Parathyroid gland
Brachial cyst (from the pharyngeal cleft)
Due to non-removal of the 2nd cleft/cervical sinus, it then becomes filled with fluid. The cyst remains stationary on swallowing.
Formation of the face
In the face, the left and right maxillary processes fuse with the frontonasal process at the midline, forming the philtrum. The left and right mandibular processes fuse at the midline to form the lower lip. Originally the Maxilla and Mandible are separated due to the division of the first pharyngeal arch. The nose is formed when the Ectodermal nasal placode covers the frontonasal process
Formation of the Palate
The palate forms in the superior oral cavity at right-angles to the facial processes. In the palate the left and right palatal processes fuse with the primary palate at the midline. The primary/primitive palate is a continuation of the maxillary processes and nasal septum.
Formation of the tongue
The tongue forms in the inferior oral cavity from 1st, 2nd, 3rd and 4th pharyngeal arches, (ventral to dorsal respectively). This accounts for the differences in cranial nerve supply to different parts of the adult tongue. The second arch regresses. In the 1st arch it is supplied by the lingual nerve which is a branch of the mandibular division of the trigeminal nerve.
Formation of a cleft lip
Due to failure in fusion of the right and left maxillary processes with the two frontonasal processes. If there is failure in one line of fusion its unilateral, when its in both lines of fusion its bilateral
Formation of a cleft palate
Due to failure in fusion of the left and right palatal processes with the primary palate. There are lines of fusion between the left palatal process and the primary palate, between the right palatal process and the primary palate, and along the midline of the secondary palate. Can be unilateral or bilateral. Midline cleft palate occurs when the fusion fails in the secondary palate
Migration and fusion of facial processes
- Migration of maxillary and mandibular processes
- Fusion of mandibular processes
- Fusion of frontonasal and maxillary processes
What do pharyngeal arch defects cause both craniofacial and cardiovascular abnormalities?
Due to neural crest cells
Treacher Collin’s syndrome
- 1st and 2nd pharyngeal arch neural crest cell defect (TCOF1)
- Underdeveloped bones of the face
- 1 in 50,000
- Face: bilateral hypoplasia of the zygomatic bone and mandible, external ear malformations, facial clefts
- Eyes: colobomas (congenital scars), downward sloping palpebral fissures, supraorbital rim formation, sparse eyelashes
Pierre Robin sequence (PRS)
Neural crest cell genetic defect (SOX9). Set of craniofacial abnormalities. 1 in 8500-1 in 14,000
Called a sequence because abnormalities occur in an order
1. mandible – micrognathia (small mandible)
2. tongue - glossoptosis (displacement)
3. pharynx - airway obstruction and cleft palate
22q11.2 deletion syndrome: DiGeorge syndrome, velocardiofacial syndrome
- Neural crest cell genetic defect (deletion on chromosome 22)
- Variable features - craniofacial dysmorphy and cardiovascular defects
- 1 in 4,000 - may be more common due to undiagnosed cases
- Face: micrognathia, small mouth, smooth philtrum, ears rotated. Problems with Maxillary/Mandibular processes- 1st pharyngeal arch.
- Cardiovascular abnormalities - 4th and 6th pharyngeal arch arteries
- Developmental delay - learning difficulties and mental illness
- Defects in the immune system- thymus, 3rd pharyngeal pouch
Cleft lip and palate
- Sometimes can just have cleft lip or can have both
- Multiple genetic and environmental causes
- Can be syndromic or non syndromic
- One of the most common craniofacial abnormality
- 1 in 750
- Neural crest and pharyngeal ectoderm contribute to palatal structures
- Can cause problems with neonatal feeding and physical abnormalities
- Repaired with surgery
