Development of the Pharyngeal Apparatus Flashcards
When do NCCs migrate into the future head and neck?
Early 4th week
What are the first pair of arches called?
Primordial jaws
What are rhombomeres (R1-7)?
Divisions of hindbrain that contribute NCC into tje pharyngeal arches.
Which rhombomeres contribute to which pharyngeal arches?
PA1 = R1-2 PA2 = R4 PA3/4 = R6/7
R3 and R5 don’t produce much NCC.
What layers are in a pharyngeal arch?
Inner endoderm.
Mesenchyme core.
Outer ectoderm.
1st arch gives rise to:
Maxillary and mandibular prominences
2nd arch does what?
Overgrows PA3/PA4 and forms cervical sinus (occurs in week 5, and disappears week 7).
What else does NCCs form?
CT, integument and smooth muscles.
What kind of mesoderm migrates into each arch?
Paraxial mesoderm
What are angioblasts from? What does it become?
From lateral plate mesoderm, and becomes endothelium.
Each arch has what components? (4)
Artery
Cartilaginous rod
Muscular component
Nerves
What do PA arteries arise from?
Truncus arteriosus
What is Meckel’s cartilage?
The cartilage of PA1.
What do dorsal parts of the Meckel’s cartilage become?
Dorsal parts break away and ossify to become malleus and incus.
What do the anterior ligament of the malleus and sphenomandibular L. come from?
Perichondrium of Meckel’s cartilage (PA1).
What does the ventral part of Meckel’s cartilage become?
The primordium of the mandible.
What is Riechert’s cartilage?
Cartilage of PA2.
What does the stapes come from?
Dorsal part of Riechert’s cartilage.
What does the ventral end of Riechert’s cartilage become?
Lesser horn of the hyoid bone
What does 3rd arch cartilage become?
It ossifies to form greater horn/cornu of hyoid
What does hypopharyngeal eminence form?
Body of hyoid.
What do the 4th and 6th PA cartilage form?
They form laryngeal cartilages (besides epiglottis).
What happens to 5th arch cartilage?
Degenerates
1st arch muscles: 2nd arch muscles: 3rd arch muscles: 4th arch muscles: 5th arch muscles:
Include innervation
1st: muscles of mastication. CN V.
2nd: stapedius m., ms. of facial expression. CN VII.
3rd: stylopharyngeus m. CN IX.
4th: cricothyroid m., levator veli palatini m. and pharyngeal constrictor ms. CN X.
6th: intrinsic ms. of larynx. CN X.
SVE supply
SVA supply
SVE: muscles derived from arches.
SVA: dermis and mucous membranes of head/neck.
Which CN supplies PA1?
CN V
Which CN supplies PA2?
CN VII
Which CN supplies PA3?
CN IX
Which CN supplies PA4-6?
CN X
3rd arch arteries become:
Dorsal aortae become:
Common carotids become:
3rd arch arteries become: common and internal carotids.
Dorsal aortae become: distal internal carotids.
Common carotids become: create external carotids de novo.
What makes primordial pharynx?
Foregut endoderm
Pharyngeal clefts, pouches and membranes
Pharyngeal clefts are external.
Pharyngeal pouches are internal.
Pharyngeal membranes separate pouches from grooves.
What does the 1st pharyngeal membrane become?
Tympanic membrane
What does 1st pharyngeal pouch become?
Ear anatomy
What does the 2nd pharyngeal pouch become?
Creates tonsillar sinus, tonsillar crypts (endoderm), lymphoid tissue (mesenchyme), lymphatic nodules.
What does 3rd pharyngeal pouch become?
Inferior parathyroids and thymus.
What does 4th pharyngeal pouch become?
Superior parathyroids
What does 1st pharyngeal grooves become?
External acoustic meatus
Where are grooves 2-4?
Lie in the cervical sinus
Cervical (Branchial) Cysts
Remnants of cervical sinus (2nd groove)
Lie free in neck, inferior to mandible.
Accumulation of fluid/cellular debris from desquamation.
How does thyroid form?
Primordial pharynx thickens and descends from tongue area and ventral to the laryngeal cartilage.
Thyroglossal duct
Connects tongue to thyroid
TH levels in:
11th wk
20th wk
35th wk
11th wk - colloid appears and TH synthesis occurs.
20th wk - fetal TSH and T3/4 increase.
35th wk - TSH and T3/4 are adult levels.
What is the ultimopharyngeal body from?
What does it form?
From the ventral part of 4th pouch. Parafollicular cells (from NCC).
Treacher-Collins syndrome (PA1 syndrome)
Deficits w/ downward slanting features, deformed, eyelids, external ears, sometimes middle and inner ears.
Ribosomes do not function –> apoptosis of cranial NCC.
Pierre Robin sequence (PA1 syndrome)
Associated w/ hypoplasia of mandible (micrognathia), cleft palate, eye/ear defects.
Thyroid hemiagenesis
UL absence of thyroid (usually Left).
Mutations in receptor for TSH usually involved.
DiGeorge syndrome
Agenesis of thyroid and parathyroid glands.
Low PTH.
Cardiac abnormalities, immune problems, etc.
