Flashcards in Pharyngeal Arches: Development of the Face and Neck Deck (112):
What are the two general phases of pharyngeal arch development?
1. Formation of pharyngeal stem
2. Development of Pharyngeal derivatives
List some birth defects involving the pharyngeal region
1. 1st Arch Syndrome
2. Auricular Cysts and sinus
3. Branchial Cysts, Sinus, Fistula
4. Cervical Thymus
5. Accessory Thymus
Sealed Cavity filled with air, pus, fluid
Cavity within a tissue, can open externally
Abnormal connection between two structures
Movement of cells during development
Growth in cell number through cell division
Mutations change patterns in migration, proliferation, etc.
How many Pharyngeal arches are there?
6, but 5th does not form
How many Pharyngeal grooves are there?
How many Pharyngeal pouches are there?
4 or 5 pairs
Where is the pharyngeal membrane located?
Where/When do pharyngeal arches emerge?
At neural tube closure around 4 weeks of development
T/F The Arches contain the ectoderm, mesoderm, and endoderm, and also neural crest
The Oropharyngeal membrane breaks down during week ________ and connects ______ to _________
3. Primitive gut
List the components of pharyngeal arches
1. Aortic Arch
2. Cartilaginous rod
3. Muscular component
5. Nueral Crest
What is the aortic arch in terms of it being a component of pharyngeal arches?
1. An artery that arises from the truncus arteriosus of the primordial heart
2. Aortic Arches arise from mesoderm, bridge between the truncus arteriosus and the dorsal aorta
What purpose does the cartilaginous rod serve?
-forms the skeleton of the arch
-Definite Structures are formed from these
What does the muscular component of pharyngeal arches do?
-Differentiates into muscles of the head and neck
What does the nerve in the pharyngeal arches do?
Supplies the mucosa and muscles derived from the arch
By the 3rd week the arches are primarily __________, but by the 4th week, primarily ___________ has migrated into the arches.
2. Neural Crest
What happens to the aortic arches of pharyngeal arches 1 and 2?
-They largely disappear
-There are some remains:
-Maxillary, ext. Carotic (1)
What happens to aortic arches 3, 4, and 6?
-They are remodeled to form portions of some large arteries
-Common and Int. Carotid (3)
-Aortic, Subclavian (4)
Where do muscles come from?
The mesoderm of the individual arches
What are the muscular derivatives of Arch 1?
Muscles of Mastication
What are the muscular derivatives of Arch 2?
Muscles of Facial expression
What are the muscular derivatives of Arch 3?
What are the muscular derivatives of Arch 4?
What are the muscular derivatives of Arch 6?
What are the sensory modalities of cranial nerves derived from?
Neural Crest and Ectodermal Placode
What are the Motor cranial nerves derived from?
What 2 main processes are formed by the 1st arch?
1. Mandibular process
2. Maxillary Process
What does the Mandibular process form?
-Lower cheek regions
-Body of the tongue
What does the Maxillary process form?
-Upper cheek regions
-Upper lip sides
What bone is associated with the 2nd arch?
What nerves are a product of the 1st arch?
V2 and V3
What muscles are a product of the 1st arch?
-All the muscles of Mastication
-Anterior Belly of the digastric
-Tensor Veli Palatini
What Skeletal components are a derivative of the 1st arch?
1. Meckel's Cartilage
Others Not highlighted in red:
-Anterior ligament of malleus
-Zygomatic bone and process
-part of temporal bone
What nerves are a derivative of Arch 2?
What muscles are derived from arch 2?
All the muscles of facial expression
-Posterior belly of the digastric
What skeletal components are derived from arch 2?
2. Styloid Process
3. Lesser horn and upper portion of body of hyoid
4. Stylohyoid ligament
What nerve is derived from arch 3?
What muscle is derived from arch 3?
What skeletal components are derived from arch 3?
Greater horn and lower portion of body of hyoid bone
What Nerves are derived from arches 4-6?
-Superior Laryngeal (4th arch)
-Recurrent Laryngeal (6th arch)
What Muscles are derived from the 4th arch?
1. Constrictors of the pharynx
3. Levator Veli Palatini
What muscles are derived from arch 6?
Intrinsic muscles of Larynx
What skeletal components come from Arches 4-6?
What is Treacher Collins syndrome?
-Congenital First arch syndrome
-Hypoplasia of arch derived facial bones:
-Down slanting of palpebral fissures
-lower eyelid colobomas
-Cleft palate and tooth defects
What Causes Congenital First arch syndromes?
Failure of the neural crest to proper migrate in to the 1st arch causing deficits in resulting tissues
What is Pierre Robin Sequence?
-Hypoplasia of the mandible (micrognathia)
-Misplacement of tongue (glossoptosis)
-Defects to the eye and ear
**Cause is unknown
Pharyngeal Grooves can also be called Pharyngeal ______
What are pharyngeal Clefts?
Indentations or pits between arches, as seen from the exterior
What are clefts lined with?
What is unique about cleft 1?
It is the only cleft NOT obliterated in development
Can clefts 2-4 persist?
Yes, in abnormal situations
Pharyngeal cleft 1 gives rise to what?
External Auditory Meatus
What would cause a preauricular sinus or cyst congenitally?
1st or 2nd arch defect
*These are often unilateral
What are two types of Branchial sinuses, cysts, or fistulas that can develop?
1. Lateral Cervical
2. Internal Branchial
Describe Lateral Cervical Sinuses, cysts, or fistulas
-Open Externally (neck)
-Failure of 2nd groove or cervical sinus to obliterate
Describe Internal Branchial sinuses, cysts, or fistulas
-Persistent 2nd pouch
-Open into intratonsillar cleft (into pharynx)
What are pharyngeal pouches?
They form as Pits INTERNALLY in the pharynx, between the arches
Pouch linings are ___________ in origin
What structure fuses on the midline during development but still retains bilateral characteristics?
What does the first pharyngeal pouch give rise to?
The middle ear
-Together with lining of 1st cleft, forms tympanic membrane (eardrum)
-Widens and forms tympanic cavity (middle ear)
-Stays narrow, forms auditory (Eustachian) tube
What are the ossicles in the middle ear derived from?
1st and 2nd arch cartilage (derived from neural crest)
What is the tympanic membrane in the middle ear derived from?
1st cleft/pouch membranes, later neural crest
What are the tympanic cavity and internal auditory meatus derived from?
What does the 2nd pharyngeal pouch give rise to?
Lining of the crypts in the palatine tonsils
Tonsils themselves are mostly composed of ________
What does the 3rd pharyngeal pouch give rise to?
Inferior parathyroid gland and the thymus
What specifically does the dorsal wing of the 3rd pouch become?
Inferior parathyroid glands
-regulates body calcium and phosphate levels
What specifically does the Ventral wing of the 3rd pouch become?
-Produces T-cells, part of the immune system
What does the 4th pharyngeal pouch give rise to?
1. Superior parathyroid gland
2. Ultimobranchial body
What specifically does the Dorsal wing of the 4th pouch give rise to?
Superior parathyroid glands
-Regulates body calcium and phosphate levels
What specifically is derived from the ventral wing of the 4th pouch?
-Embryonic structure will contain C-cells of thyroid (regulate calcium levels via calcitonin)
T/F the Ventral 4th pouch is sometimes considered a 5th pouch
T/F Primordia originate at mature functional sites
FALSE, they need to migrate
What is Cervical Thymus?
-Abnormality resulting from defects in migration
-Cord of thymus persists in neck on path of descent
-This is rare
What is Accessory Thymus?
-Abnormality resulting from defect in migration
-Piece of thymus remaining in path of descent
List 4 typically benign abnormalities resulting from defects in migration
1. Undescended parathyroid gland
2. Accessory thymic Issue
3. Persistent cord of thymic tissue
4. Ectopic inferior parathyroid gland
What is DiGeorge Syndrome?
-Failure of 3rd and 4th pouches to differentiate into thymus, parathyroid
-Neural Crest Defects
-Variability in severity and outcome
What are the predominan defects for DiGeorge Syndrome? (Catch 22)
Cardiac Abnormality (especially Tetralogy of Fallot)
What are the 4 things present in a heart showing Tetralogy of fallot?
1. Overriding Aorta
2. Pulmonic Stenosis
3. Ventricular Septal Defect
4. Right Ventricular hypertrophy
Generally speaking, define a pharyngeal membrane
They form where the epithelia of the grooves and pouches approach each other
What are the 2 pharyngeal membranes?
1. Oropharyngeal Membrane
2. Tympanic membraine
Describe the Oropharyngeal membrane
1. Strictly speaking, not a pharyngeal membrane
2. Breaks down in 4th week to connect the mouth (stomodeum) with the gut/pharynx
3. marks site where ectoderm and endoderm meet
4. Glossopalatine arch marks location, separates oral cavity from pharynx
Describe the Tympanic membrane
-Derived from layers between 1st cleft and 1st pouch
-1st ectoderm and endoderm only, then neural crest moves
What do Hox genes regulate?
What are Hox genes involved in?
Bodily segmentation during embryonic development
What type of DNA sequence is a homeobox?
180 bp DNA sequence
As a transcription factor what to they turn on?
Cascades of other genes
What patterns the Neural crest in the Proximal-Distal orientation?
What does the tongue develop from?
The floor of the arches
Which arches form which parts of the tongue? Generally speaking
Arch 1: forms anterior 2/3 of the tongue epithelium
Arch 2: it is covered up as arch 3 portion grows
Arch 3: Forms most of the remaining 1/3 of tongue epithelium
Arch 4: Forms just a bit of tongue at the very back of the throat
For tongue development, what does arch 1 form at weeks 4 and 5 respectively?
Week 4: Forms median swelling: Median tongue bud (tubercular impar)
Week 5: forms lateral swellings: distal tongue buds (lateral lingual swellings)
What does arch 2 form at week 4 to develop the tongue?
Forms midline swelling called Copula
What does arch 2 form at 5-6 weeks to develop the tongue?
Is overgrown by hypopharyngeal eminence from Archese 3, 4
Where does epiglottis arise?
Posterior to hypopharyngeal eminence
What gives rise to the tongue muscles?
What is the terminal sulcus on the tongue?
-Dividing line between oral tongue and pharyngeal tongue
-Dividing line between anterior 2/3 and posterior 1/2
-It is between CN V and CN IX innervation
-Except circumvallate Papillae--innervated by CN IX but anterior to the sulcus
What is the foramen cecum the sit for?
T/F Origination of the thyroid is bilateral
FALSE, it originates on the midline
What is an endodermal diverticulum?
-Forms during the development of the thyroid gland just posterior to the floor of the 1st arch (This is not a pharyngeal pouch)
-It is NOT biliateral: originates on the midline
-Elongates into the thyroglossal duct
What is the thyroglossal duct?
-Elongation of the Diverticulum
-Gland remainsin contact with tongue early, but duct is normally obliterated later in development
Where does the Thyroglossal duct connect with the tongue?
What are the thyroid anomalies?
Thyroglossal duct cysts and sinuses
Why do thyroid anomalies form?
Failure of thyroglossal duct to completely pinch off and degenerate
Where an thyroglossal anomalies form?
May form anywhere along the course followed by the thyroglossal duct
By what age are most thyroglossal anamolies seen?
Most seen by 5 yrs old
T/F most thyroid anomalies are symptomatic