Embryology 2nd lecture

Question 1

Pharyngeal arch endoderm derivatives: pharyngeal pouch 3

Answer 1

—Ventral bud > thymus

—Dorsal bud > inferior parathyroid (inferior because dorsal bud gets dragged down with thymus)

Question 2

Pharyngeal arch endoderm derivatives: Pharyngeal pouch 4

Answer 2

—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)

Question 3

Pharyngeal arch endoderm derivatives: žPharyngeal pouch 2

Answer 3

—Palatine tonsilar bed/fossa à induces lymphoid tissue invasion and together form the palatine tonsil

Question 4

Pharyngeal arch endoderm derivatives: žPharyngeal pouch 1

Answer 4

Tubotympanic recess > tympanic cavity, mastoid antrum, auditory tube

Question 5

Summary: endoderm derivatives

Arches

1

2

3

4

Answer 5

Derivatives

1. Middle ear cavity, auditory tube
2. Palatine tonsil
3. Inferior parathyroid glands ,Thymus
4. Superior parathyroid glands ,Ultimobranchial bodies

Question 6

Pharyngeal groove/cleft transformation:

žPharyngeal groove 1

Answer 6

žPharyngeal groove 1

—External acoustic meatus

Question 7

Pharyngeal groove/cleft transformation:

žPharyngeal groove 2-4

Answer 7

žPharyngeal 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

Question 8

Clinical Correlation: žPharyngeal groove/crest transformation 2-4

cyst

Answer 8

žCervical (branchial) cyst

—Persistent cervical vesicle

—Presents as asymptomatic swelling on lateral neck, anywhere along the anterior border of sternocleidomastoid

Question 9

Development of the thyroid gland:

žStep 1:

Answer 9

Endoderm between pharyngeal arch 1 & 2 form a thyroid primordium in the midline and invaginate caudally

—

Question 10

Clinical Correlation: žPharyngeal groove/crest transformation 2-4

sinus and fistula

Answer 10

žCervical (branchial) sinus

—Persistent cervical sinus or any cleft/pouch

žCervical (branchial) fistula

—Continuous duct between pharynx and neck surface

Question 11

Development of the thyroid gland:

žStep 2:

Answer 11

žStep 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

ž

Question 12

Development of the thyroid gland:

žStep 3:

Answer 12

žStep 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

Question 13

Development of the thyroid gland:

žStep 4:

Answer 13

žStep 4:

žThyroglossal duct degenerates

—Portion of it may become the pyramidal lobe of thyroid

Question 15

Development of the thyroid gland:

žStep 5:

Answer 15

žStep 5:

žForamen cecum becomes a remnant (indentation) between anterior & posterior tongue

Question 16

Development of Thyroid Gland: Summary

Steps 1-5

Answer 16

ž1. Endoderm between pharyngeal arch 1 & 2 form a thyroid primordium in the midline and invaginate caudally

ž2. As the thyroid primordium grows caudally, it is still open to the pharynx via thyroglossal duct which opens into pharyngeal space at foramen cecumž

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

ž4. Thyroglossal duct degenerates

—Portion of it may become the pyramidal lobe of thyroid

ž5. Foramen cecum becomes a remnant (indentation) between anterior & posterior tongue

—

Question 17

Clinical Correlation of Thyroid Development

Answer 17

žThyroglossal 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

Question 18

Development of the Tongue:

1st and 2nd arches

Answer 18

ž1st arch*

—Median lingual swelling (tuberculum impar)

—Lateral lingual swellings > Ant 2/3 of the tongue *(ectoderm lined)

ž2nd arch - —Copula

Question 19

Tongue Devolment:

ž3rd & 4th arches

Answer 19

ž3rd & 4th arches

—Hypopharyngeal eminence > Post 1/3 of the tongue

Question 20

žLandmarks derived from developmental process of tongue?

Answer 20

žLandmarks 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?

Question 21

Skeletal muscles of the tongue derive from _________. Which migrate into the tongue after the _____ week, pulling in _________ innervation.

Answer 21

žSkeletal muscles of the tongue derive from occipital somites.

—Migrate into tongue after 5th week, “pulling in” the motor innervation: Hypoglossal nerve

Question 22

Innervation of the Tongue

žAnterior 2/3

Answer 22

žAnterior 2/3

—Somatosensory – V2

—Special sensory - VII

Question 23

žPosterior 1/3 innervation of tongue

Answer 23

žPosterior 1/3

—Somatosensory – IX & X

—Special sensory - IX

Question 24

Muscle innervation of tongue

Answer 24

Hypoglossal : 12