Embryology Flashcards
Pharyngeal (branchial) apparatus
- Mesenchyme bars that surround the developing foregut and neural tube.
- Consists of pharyngeal arches, pouches, grooves and membranes.
- 1st observed during wk 4
What is the endodermal lining of the pharyngeal apparatus?
The primitive gut tube
Pharyngeal Arch
Core–from mesoderm, has its own blood and nerve supply.
Contributions form all 3 embryonic layers
6 arches, but 5 is rudimentary
Pharyngeal cleft
Each external depression (invagination) between arches. Covered with surface ectoderm
Pharyngeal pouch
Depressions viewed from the inside between the arches. Numbered rostral to caudally. Lined with endoderm. Diverticula of the pharynx.
Pharyngeal membrane
Where clefts and pouches meet each other during development.
Where does the mouth form?
Between the maxillary and mandibular prominence of the 1st pharyngeal arch. Site marked by buccopharyngeal membrane.
What forms the initial shape of the arches?
Lateral plate mesoderm
Where does the mesoderm that migrates to the arches come from?
Somites and somitomeres
What forms rostral somitomeres?
Eye muscle precursors
What forms occipital somites?
Tongue precursors
Is the migration of neural crest cells random or highly regulated?
Highly regulated (unlike mesenchymal movements)
What is the origin of neural crest cells?
Neuroectoderm
Elements present in each arch
Skeletal, muscular, neural, vascular
Cranial nerves and pharyngeal arches
Each arch is supplied by a single cranial nerve.
How are the cranial nerves formed?
Neurons from the brain and cranial ganglia grow into specific arches forming the cranial nerves
What are the branches that are derived from pharyngeal arches called?
Special visceral efferents. (Branchiomotor)
Aortic Arch arteries
Each pharyngeal arch contains an artery that develops in conjunction with the heart and the vascular system
What are the developmental axioms?
- tubular structures can be stenotic or atretic
- fusing structures can remain divided
- obliterated structures can persist
Possible locations for stenosis/atresia during development. (anatomical aberrations)
Ear canal, nasal passage, larynx, esophagus, trachea
Possible locations for clefts during development (anatomical aberrations)
Ear pit, nasal masses, face, lip, palate, larynx, tracheal-esophageal
Potential persistent structures in development
Thyroglossal duct, branchial cleft
When do thyroid endocrine glands first appear?
24 days (midway in the 4th week)
When does the thyroid reach it’s position anterior to the trachea?
7th week
What connects to the thyroid to the tongue?
Thyroglossal duct. Connects when the thyroid is travelling
Where does the tongue develop?
In the floor of the pharynx
What does the tongue develop from?
Mesenchyme of first 4 pharyngeal arches.
Where does the midline diverticulum of the thyroid travel?
Travels ventral to hyoid and laryngeal cartilages
How often is the pyramidal lobe of the thyroid present in people?
50% of the time
What cells develop from the thyroid diverticulum?
Follicular cells
What cells develop from the 4th pharyngeal arch?
Parafollicular cells (from ultimobranchial body)
Branchial cleft anatomy
Branches deep to the branchial arch derivatives it’s named after.
Development of anterior 2/3 of the tongue
2 distal tongue buds and 1 median tongue bud form rostral to foramen cecum. Distal tongue buds overgrow median bud and merge together.
What does the median sulcus represent?
Line of fusion of distal tongue buds
What does the terminal sulcus identify?
Boundary between anterior 2/3 and posterior 1/3 of tongue and former buccopharyngeal membrane site.
Development of the posterior 1/3 of tongue
Copula and hypobranchial eminence develop in the floor of the pharynx. Hypobranchial eminence overgrows the copula.
Is the 2nd arch a contributor to the definitive adult tongue?
No. It is overgrown by the mesenchyme from the 3rd arch.
What do the epiglottis and extreme posterior part of the tongue develop from?
A midline swelling in the 4th arch.
What does the palatoglossus develop from?
The head mesenchyme
What do the rest of the tongue muscles (except the palatoglossus) derive from?
Myoblasts that migrate from the occipital myotomes along with hypoglossal nerve.
Sensory innervation to the anterior 2/3 of the tongue (GSA and taste)
GSA: lingual nerve (branch of V3)
Taste: Chorda tympani branch (off facial n.)
Sensory innervation to the posterior 1/3 of the tongue (GVA and taste)
GVA: branches of CN IX and X
Taste: CN IX
Sensory innervation for the epiglottis and extreme posterior of the tongue
GVA: CN X
Taste: CN X
Motor innervation of the tongue
Hypoglossal nerve supplies motor to all the tongue except the palatoglossus
Pituitary gland formation
Evagination of the endothelium upward from the roof of the pharynx to the developing brain to form the glandular portion. Evagination downward toward the pharynx from developing hypothalamus forms the neural portion (neurohypophysis)
Which portion of the pituitary gland is developed from the endothelium of the pharynx?
Then adenohypophysis
