Embryology 2nd lecture Flashcards
Pharyngeal arch endoderm derivatives: pharyngeal pouch 3
Ventral bud > thymus
Dorsal bud > inferior parathyroid (inferior because dorsal bud gets dragged down with thymus)
Pharyngeal arch endoderm derivatives: Pharyngeal pouch 4
Ventral bud > ultimopharyngeal body (parafollicular cells in thyroid that produce calcitonin)
Dorsal bud > superior parathyroid (superior because inferior parathyroid of arch 3 dorsal bud gets dragged down with thymus)
Pharyngeal arch endoderm derivatives: Pharyngeal pouch 2
Palatine tonsilar bed/fossa à induces lymphoid tissue invasion and together form the palatine tonsil
Pharyngeal arch endoderm derivatives: Pharyngeal pouch 1
Tubotympanic recess > tympanic cavity, mastoid antrum, auditory tube
Summary: endoderm derivatives
Arches
1
2
3
4
Derivatives
- Middle ear cavity, auditory tube
- Palatine tonsil
- Inferior parathyroid glands ,Thymus
- Superior parathyroid glands ,Ultimobranchial bodies
Pharyngeal groove/cleft transformation:
Pharyngeal groove 1
Pharyngeal groove 1
External acoustic meatus
Pharyngeal groove/cleft transformation:
Pharyngeal groove 2-4
Pharyngeal groove 2-4
Coalesce into cervical sinus as arch 2 and 4 expand as folds toward each other and once the folds fuse, the sinus becomes the cervical vesicle
The neck line becomes smooth and cervical vesicle degenerates over time
Clinical Correlation: Pharyngeal groove/crest transformation 2-4
cyst
Cervical (branchial) cyst
Persistent cervical vesicle
Presents as asymptomatic swelling on lateral neck, anywhere along the anterior border of sternocleidomastoid
Development of the thyroid gland:
Step 1:
Endoderm between pharyngeal arch 1 & 2 form a thyroid primordium in the midline and invaginate caudally
Clinical Correlation: Pharyngeal groove/crest transformation 2-4
sinus and fistula
Cervical (branchial) sinus
Persistent cervical sinus or any cleft/pouch
Cervical (branchial) fistula
Continuous duct between pharynx and neck surface
Development of the thyroid gland:
Step 2:
Step 2: As the thyroid primordium grows caudally, it is still open to the pharynx via thyroglossal duct which opens into pharyngeal space at foramen cecum
Development of the thyroid gland:
Step 3:
Step 3: Thyroid primordium continues to grow down below the hyoid bone and takes resident anterior to trachea, caudal to larynx, and matures into thyroid gland
Development of the thyroid gland:
Step 4:
Step 4:
Thyroglossal duct degenerates
Portion of it may become the pyramidal lobe of thyroid
Development of the thyroid gland:
Step 5:
Step 5:
Foramen cecum becomes a remnant (indentation) between anterior & posterior tongue
Clinical Correlation of Thyroid Development
Thyroglossal duct cyst (TDC)
Cystic remnant of thryoglossal duct
Most common mass in the midline of the neck in children
Most commonly present at the level of hyoid bone
May contain ectopic thyroid tissue
Development of the Tongue:
1st and 2nd arches
1st arch*
Median lingual swelling (tuberculum impar)
Lateral lingual swellings > Ant 2/3 of the tongue *(ectoderm lined)
2nd arch - Copula
Tongue Devolment:
3rd & 4th arches
3rd & 4th arches
Hypopharyngeal eminence > Post 1/3 of the tongue
Landmarks derived from developmental process of tongue?
Landmarks derived from developmental process
Line of fusion between two lingual swellings à Median sulcus
Line of fusion between arch 1 and hypopharyngeal eminence à terminal sulcus
Foramen cecum?
Skeletal muscles of the tongue derive from _________. Which migrate into the tongue after the _____ week, pulling in _________ innervation.
Skeletal muscles of the tongue derive from occipital somites.
Migrate into tongue after 5th week, “pulling in” the motor innervation: Hypoglossal nerve
Innervation of the Tongue
Anterior 2/3
Anterior 2/3
Somatosensory – V2
Special sensory - VII
Posterior 1/3 innervation of tongue
Posterior 1/3
Somatosensory – IX & X
Special sensory - IX
Muscle innervation of tongue
Hypoglossal : 12
