Head and Neck Embryo (see slides too) Flashcards
Each pharyngeal arch consists of what four components?
a core of mesenchyme (derived from neural crest cells [e.g., ectomesenchyme] and mesoderm) pharyngeal cleft (an external lining of surface ectoderm) pharyngeal pouch (internal lining of endoderm) pharyngeal membrane (between the clefts and the pouches, where the outer layer of ectoderm meets the inner layer of endoderm.
A thin layer of mesenchyme separates the ectoderm and endoderm).
Each pharyngeal arch contains
a bar of cartilage (derived from neural crest cells)
a muscle component (not pictured here; derived from paraxial mesoderm)
a cranial nerve (derived from the neural tube)
An aortic arch artery (derived from the visceral layer of lateral plate mesoderm).
Recall that the muscle component MIGRATES into the arch from where it develops in the paraxial mesoderm, dragging its nerve supply with it.
1) The endodermally-lined pharyngeal FLOOR gives rise…
2) The endodermally lined POUCHES are maintained and give rise…
1) to ventral, unpaired adult structures, including the tongue and thyroid gland.
2) to a number of important organs, labelled in the image on the right.
Describe how the tonsil gains immune function.
Later in development, the tonsils are invaded by lymphatic tissue.
What is the tonsilar fossa? What pouch is it derived from?
Part of the 2nd pouch remains in the adult as the tonsillar fossa.
What pharyngeal arch does the anterior 2/3 of the tongue derive from? What are the swellings that the tongue derive from?
two lateral lingual swellings
one medial swelling (the tuberculum impar)
originate from the floor of the first pharyngeal arch.
What pharyngeal arch does the posterior 1/3 of the tongue derive from? What is the swelling that the tongue derives from?
The hypopharyngeal eminence (copula) appears
the floor of the third pharyngeal arch
Describe the innervation tongue… General sensory Anterior? Taste anterior? General sensory Posterior? Taste posterior? Sensory epiglottis and extreme posterior tongue? Motor (all)?
Anterior general sensory: mandibular V3 of trigeminal n (pharyngeal arch 1)
Anterior taste: CN VII via chora tympani n.
Posterior sensor: glossopharyngeal (CN IX) (pharyngeal arch 3)
Taste posterior: CN X
The epiglottis and extreme posterior part of the tongue: superior laryngeal nerve (CN X) (pharyngeal arch 4-6)
Motor: hypoglossal (CN XII) (from occipital somites and intrinsic muscles of tongue)
Describe the development of the thyroid gland…
Which germ layer?
What part of the tongue does the thyroid originate from?
Does it descend anterior or posterior to the laryngeal skeleton?
a diverticulum of the foregut at a point of the foramen caecum (which separates the anterior 2/3 from the posterior 1/3 of the tongue).
The thyroid descends anterior to the gut tube, hyoid bone, and laryngeal cartilages to assume its final position.
Describe the formation of the nasal cavity and choanae.
The nasal pit deepens
the oronasal membrane separates the pits from the oral cavity.
The oronasal membrane ruptures, forming the primitive choanae.
Describe the development of the paranasal sinuses.
Paranasal sinuses develop as diverticula of the lateral nasal wall and extend into the maxilla, ethmoid, frontal, and sphenoid bones.
At what age do the paranasal sinuses reach their maximum size?
They reach their maximum size during puberty and contribute to the definitive shape of the face.
1) What does the primary palate derive from?
2) What does the nasal septum derive from?
1) intermaxillary segment of the frontonasal prominence.
2) Also from the frontonasal prominence
What does the secondary palate derive from?
lateral palatine processes (or palatine shelves).
Describe the development of the secondary palate in relation to the tongue.
The lateral palatine pocesses are vertically placed on either side of the tongue.
The tongue moves down in the oral cavity (subsequent to growth of the mandible)
the palatal shelves swing up and fuse in the midline with each other, as well as the primary palate.
