DEVELOPMENT OF THE HEAD AND NECK - 2

DEVELOPMENT OF THE MOUTH:

o The Breakdown of the Buccopharyngeal Membrane marks the future mouth. It is very important to the embryo, as it allows for communication of amniotic fluid between the inside (gut) of the embryo and the environment.

DEVELOPMENT OF PARATHYROID:

Reiterated from above. There are four parathyroid glands on the thyroid, two superior and two inferior.

o The two Inferior Parathyroids are formed from Pouch III. Pouch III forms the inferior ones because it also forms part of the Thymus which migrates down to the Anterior Mediastinum, hence the third pouch is dragged down a bit with it.

o The two Superior Parathyroids are then formed by Pouch IV.

DEVELOPMENT OF THE THYROID GLAND:

Starts in the floor of the pharynx and then works its way down.

o For a short time it remains connected to the pharynx by a thyroglossal duct which disintegrates in the adult, leaving behind the remnant of the foramen cecum of the tongue.

DEVELOPMENT OF THE TONGUE:

o All tongue muscles are somite-derived -- not branchial arches!

o Anterior 2/3: Formed from lateral lingual swellings from arch 1 mesenchyme.

o Posterior 1/3: From hypobranchial eminence from arch 3 mesenchyme.

DEVELOPMENT OF THE FACE:

• It forms from five processes.
• FRONTONASAL PROCESS: Forms Nasal Processes and Globular Processes
• PAIRED MAXILLARY PROCESSES: Grows toward the midline to meet each other.
• PAIRED MANDIBULAR PROCESSES: Grows toward the midline to meet each other.
• Process:
• First, Olfactory Pits form in the Frontal Process.
• The Frontal Processes then grow around these pits, forming the following:

§ 2 Lateral Nasal Processes -- Forms the lateral ala of nose.

§ 1 Medial Nasal Process -- Forms philtrum.

§ 2 Globular Processes, on the end of the Lateral Nasal Processes. They fuse together to form the premaxilla.

· CLEFT LIP: Failure to join of the Maxillary Process and Globular Process. Could be on the same side or bilateral.

· Hare Lip: A midline cleft. Very uncommon.

· CLEFT PALATE: An opening between the nasal and oral cavities, caused by a failure of the maxillary shelves to come together and fuse.

o This is a different etiology then cleft lip! Although they commonly occur together.

BRANCHIAL FISTULA:

Failure of the Branchial clefts to disappear. The cleft stays completely open. They are located on the side of the neck.

BRANCHIAL SINUS: Incomplete breakdown of the branchial clefts. The cleft is partially open, either to the inside or outside.

They are located on the side of the neck.

FIRST ARCH SYNDROMES: Rare syndromes involving the first arch. Due to middle ear ossicles, these syndromes lead to deafness.

Category: Anatomy Notes