Pharyngeal apparatus

Question 1

What is Treacher Collins syndrome?

Answer 1

• eyes are characterized by an antimongoloid slant of the palpebral fissures and hypoplasia of the lower lids and the lateral canthi, including the partial absence of the eyelid cilia.
  
  • Down slanted eyes = antimongoloid slant
  • Absent anti-helical fold in the ear
  • The appearance of the mispositioned adnexal structures is a
  • reflection of both zygomatic–orbital dystopia and hypoplasia of the soft tissues.
  • The maxilla and the mandible are also deficient and malformed.
  • He was found to have congenital heart defects and renal malformation
  • Pharyngeal, arches have the components of neural crest cells
  • If the pattern t has underdeveloped face they may also have heart problems as the migration of the neural crest cells not migrating properly
    Pharyngeal, arches form between the 2snd to the 29th day

Question 2

What are pharyngeal arches, cleft and pockets?

Answer 2

• Each pharyngeal arch consists of a core of mesenchyme (pink), has an outer covering of
  
  • ectoderm and is lined internally by endoderm.
  • The ectoderm appears as the pharyngeal clefts (grooves) between the arches
  • The endoderm as the pharyngeal pouches inside- numbered 1, 2, 3, 4 and 6, form in craniocaudal
  • sequence – 5th week
  • mesenchyme derived from the neural crest, the lateral plate mesoderm and the paraxial mesoderm
  • Endoderm forms pouches
  • Ectoderm forms cleft
  • Mesoderm forms arch
  • The mesenchyme in each pharyngeal arch differentiates into a cartilage, the associated
  • muscle, and an aortic arch artery.
    ○ The cartilage can also differentiate into bone
  • Each pharyngeal arch also contains a cranial nerve that enters it from the developing brainstem

Question 3

What are pharyngeal arches? (need to know this)
LOOK ON THE NOTES

Answer 3

• Nerves will innervate the structures that derived from the same arch as them
  
  • Trigeminal innervates all muscles of mastication as they are both derived from the 1st branch
  • Facial nerve innervates all muscles of facial expression as they are both derived from the 2nd branch
  • The anterior digastric is from the 1st arch and posterior digastric is from the 2nd arch so they are innervated by different nerves
  • 5th arch disappears so you only see 5 arches
  • 4th and 6th both by vagus
  • 4th by superior laryngeal nerve
  • 6th recurrent laryngeal nerve
  • Both are the Vagus

Question 4

What are pharyngeal clefts?

Answer 4

• 4 pharyngeal clefts
  
  • Made from the ectoderm
  • 1st cleft-external auditory meatus
  • 2nd cleft-cervical sinus (disappears)
  • 3rd cleft-cervical sinus (disappears)
  • 4th cleft-cervical sinus (disappears)

Question 5

What are pharyngeal pouches?

Answer 5

• 4 pharyngeal pouches
  
  • Made form endoderm
  • 1st pouch
    ○ Auditory tube
    ○ On the outside (cleft) produces the external auditory meatus
  • 2nd pouch
    ○ Palatine tonsils
  • 3rd pouch
    ○ Inferior parathyroid gland
    ○ Thymus
  • 4th pouch
    ○ superior parathyroid gland
    ○ Ultimobranchial body
    ○ Cervical sinus
  • Only the 1st pharyngeal cleft is in adults the rest disappear
  • Ectoderm from 1st pharyngeal, cleft migrates down and fuses with the 2,3,4 cleft
  • The overhanging area is called the cervical sinus which usually disappears, if it doesn’t disappear it will turn into cyst

Question 6

What is the importance of the thymus?

Answer 6

• Derives from the 4th pharyngeal pocket along with the inferior parathyroid
  
  • Thymus is developed in the neck then migrates into the thorax on fort of the heart. When it immigrates it brings the inferior parathyroid to the thorax
  • This means that also the inferior parathyroid (4th pocket) grew above the superior parathyroid (6th pocket) the inferior will end up bellow the superior as it is dragged by the thymus

Question 7

How is the cervical sinus created?

Answer 7

• The second pharyngeal arch enlarges and grows rapidly as a flap over the remaining
  
  • three pharyngeal clefts.
  • This flap contains the platysma muscle and fuses below with the epicardial bulge covering the heart.
  • Remnants of lower clefts lined with ectoderm may remain beneath the flap, forming a cervical sinus , but this is normally obliterated
  • When the cervical sinus persists this is created
  • On the anterior border of the sternocleidomastoid
  • Usually won’t see the cyst until puberty or adulation hood as the cyst will expand and become more visible

Question 8

What is DiGeorge syndrome and explain it?

Answer 8

• DiGeorge syndrome is a condition present from birth that can cause a range of lifelong problems, including heart defects and learning difficulties
  
  • Microdeletion chromanone 22
  • Birth defect
  • Effects immune system
  • Absence of or underdeveloped thymus And parathyroids
  • Facial features: low set ears, wide-set eyes, small jaw and bowing of the upper lip
  • 3rd and 4th pouches are under developed
  • Effects immune system because the thymus is under developed (t cells not made)

Question 9

Tell me about now neural crest cells influence the development.

Answer 9

• Neural crest cells are essential for formation of much of the craniofacial region. Consequently, disruption of crest cells development results in craniofacial malformations.
  
  • As neural crest cells also contribute to the conotruncal endocardial cushions, which septate the outflow tract of the heart into pulmonary and aortic channels, many infants with craniofacial defects also have cardiac abnormalities.
    Unfortunately, crest cells appear to be a particularly vulnerable cell population and are easily killed by compounds such as alcohol and retinoic acid

Question 10

How is the tongue developed?

Answer 10

• Near the end of week 4, as a result of first arch mesenchymal proliferation, a median lingual swelling /tuberculum impar, and two lateral lingual swellings begin to develop cranial to the foramen cecum - form the anterior two-thirds of the tongue.
  
  • The copula, develops from the second arches
  • The hypopharyngeal eminence, a swelling of tissue from the ventromedial third and fourth pharyngeal arches - posterior one- third of the tongue and the region of the epiglottis and the
  • extreme posterior part of the tongue respectively.
  • terminal sulcus divided the tongue into anterior 2/3 and posterior 1/3
  • Taste buds can be seen by eye or by microscope

Question 11

How is the thyroid gland developed?

Answer 11

Early in week 4, a small bud, the thyroid primordium – thyroglossal duct, develops from the endoderm of the embryonic pharynx and combines with tissue from the two lateral fourth pharyngeal pouches.
The thyroglossal duct forms the follicular cells, whereas the lateral pouch components provide the parafollicular cells (C cells).
With the growth of the embryo and the thyroglossal duct, the developing thyroid passes ventral to the developing hyoid bone and laryngeal cartilages.
Connectivity with the tongue is maintained briefly by the thyroglossal duct.
At 7 weeks, the thyroid primordium has divided into right and left lobes, connected by the isthmus, and it has assumed its normal location in the neck.
The thyroglossal duct normally degenerates by the end of the fifth week