Embryo of Pharyngeal Apparatus Flashcards by Staci Thomas

What is part of the pharyngeal apparatus?

Pharyngeal Arches
Pouches
Grooves (clefts)
Membranes

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What does the pharyngeal apparatus contribute to the formation of?

Nasal cavities 
Mouth
Larynx
Pharynx 
Neck

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The Pharyngeal Arches develop early in the 4th week as _______ _______ _______ migrate into the future head and neck.

Neural Crest Cells

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The 1st pair of pharyngeal arches, the _______ _______, appear lateral to the developing pharynx.

Primordial Jaws

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What type of embryonic cells make up the pharyngeal arches?

Externally = Surface ectoderm
Internally = Endoderm 
Core = Mesoderm and Mesenchyme

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What is mesenchyme derived from?

Migratory Neural Crest Cells

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What is head mesoderm derived from?

Forms from Paraxial Mesoderm

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This component of the Pharyngeal Arches forms all CT in the head, including the dermis (integument) and smooth muscle.

NCC-derived Mesenchyme

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This Pharyngeal Arch component populates each arch to form musculature.

Paraxial Mesoderm

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This component of the Pharyngeal Arch consists of angioblasts that differentiate into endothelium.

Lateral Plate Mesoderm

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This component of the Pharyngeal Arch makes up extra ocular musculature (i.e., Orbicularis Oculi).

Prechordal Plate Mesoderm

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What does Pharyngeal endoderm do?

Plays essential role in regulating development of the arches

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What are the main structures of the Pharyngeal Arches?

1) Cartilaginous rod – forms skeletal elements
2) Muscular component – becomes muscles in head/neck
3) Cranial nerves – with sensory and/or motor
4) Arch artery

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Where does the Arch Artery arise from?

Truncus Arteriosus of the primordial heart

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What is the cartilage of PA 1?

Meckel’s Cartilage

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What will develop from Meckel’s Cartilage (PA 1)?

Malleus 
Incus
Mandible 
Sphenomandibular L.
Anterior L. of Malleolus

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What is the cartilage of PA 2?

Riechert’s Cartilage

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What will develop from Riechert’s Cartilage (PA 2)?

Stapes
Styloid Process of Temporal bone
Stylohyoid L.
Lesser Cornu of Hyoid bone

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What will develop from the PA 3 cartilage?

Greater Cornu of Hyoid bone

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The body of the Hyoid bone is formed by the __________ __________. This is a prominence in the floor of the embryonic pharynx from PA 3 and PA 4.

Hypopharyngeal Eminence

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What will develop from the PA 4 and PA 6 cartilages?

Laryngeal Cartilages (both)
Epiglottis (PA 4 only)

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What are the muscular components of the Pharyngeal Arches derived from?

Paraxial Mesoderm
Prechordal Plate (extraocular muscles)

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What muscular components come from PA 1?

ChewOnThat

Muscles of Mastication

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What muscular components come from PA 2?

SmileAndSayCheese

Stapedius M.
Muscles of Facial Expression

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What muscular components come from PA 3?

Stylopharyngeus M. #ElevateAndDilate

What muscular components come from PA 4?

Cricothyroid M. Levator Veli Palatini M. Pharyngeal Constrictors #PushItPushItRealGood

What muscular components come from PA 6?

Intrinsic muscles of the Larynx #SoundOff

What cranial nerves innervate the Pharyngeal Arches?

PA 1 -- CN V PA 2 -- CN VII PA 3 -- CN IX PA 4/6 -- CN X

This PA nerve supplies the first arch. It is the principal sensory nerve of the head and neck, and motor nerve for muscles of mastication.

CN V -- Trigeminal ***Only branches V2 and V3

This PA nerve supplies the second arch. It innervates the muscles of facial expression.

CN VII -- Facial

This PA nerve supplies the third arch. It innervates the Stylopharyngeus muscle.

CN IX -- Glossopharyngeal

This PA nerve supplies 4th/6th arches.

CN X -- Vagus

For PA 4/6, what specific branches of CN X innervate them?

4 - Superior Laryngeal N. (branch of CN X) | 6 - Recurrent Laryngeal N. (branch of CN X)

Arteries arising from 1st-3rd aortic arch arteries are (BILATERAL/ASYMMETRICAL), while 4th and 6th are (BILATERAL/ASYMMETRICAL).

Bilateral | Asymmetrical

The aortic arch artery system initially consists of 5 pairs of arteries that arise from the _______ ______, which is a basket-like structure arising from the dorsal aorta. They are remodeled into great arteries of the thorax, head, and neck.

Aortic Sac

Externally, these are located between each Pharyngeal Arch and are covered with surface ectoderm.

Pharyngeal Grooves

Pharyngeal endoderm lines the pharynx internally, creating ________ _______ between each arch.

Pharyngeal Pouches

What arises from the 1st PA groove?

External Acoustic Meatus

What happens to grooves 2-4?

They are in the Cervical Sinus and will go away. ***Not worried about them for test.

There are five pairs of Pharyngeal Pouches that develop in a craniocaudal sequence between the arches. The 1st pair lies between which arches?

1st and 2nd Pharyngeal Arches

T/F. Birth defects of the 1st groove are common.

False. Birth defects of the 2nd groove are common.

These can be caused by remnants of the Cervical Sinus and/or the 2nd Groove. They persist and form a slowly enlarging, painless, free-lying cyst in the neck, inferior to the angle of the mandible.

Cervical Cysts ***Least problematic -- Not closed internally

What causes Cervical Cysts?

Accumulation of fluid and cellular debris derived from desquamation of their epithelial linings.

This is caused by a failure of the 2nd PA groove and Cervical Sinus to obliterate. It is detected due to a discharge of mucous and is typically bilateral and commonly associated with auricular sinuses.

Cervical Sinus

This is an abnormal canal that opens into the Tonsillar Sinus and externally in the side of the neck. It is caused by the persistence of parts of the 2nd Groove and Pouch.

Cervical Fistula ***Can pass through branches of Carotid arteries

These form where the pharyngeal pouch endoderm contacts the ectoderm of the pharyngeal grooves.

Pharyngeal Membranes

Pharyngeal Membranes are quickly infiltrated by...

Mesenchyme

The 1st Pharyngeal Membrane and the intervening mesenchyme form the...

Tympanic Membrane ***All other membranes get obliterated (Not worried about them for test)

What develops from the 1st Pharyngeal Pouch?

Tympanic Cavity Mastoid Antrum Pharyngotympanic Tube (Eustachian Tube)

What develops from the 2nd Pharyngeal Pouch?

``` Tonsillar Sinus Tonsillar Epithelium (from endoderm) Lymphoid Nodules (from mesenchyme) ```

What develops from the 3rd Pharyngeal Pouch?

Inferior Parathyroid Gland | Thymus

What is special about the migration of the things developed from the 3rd Pharyngeal Pouch?

They migrate south, due to growth of brain and cardiac regions. This is why the Inferior Parathyroid Gland develops ABOVE the Superior Parathyroid Gland. It will eventually migrate below it.

What develops from the 4th Pharyngeal Pouch?

Superior Parathyroid Gland | Ultimobranchial Body

What does the Ultimobranchial Body (from 4th pouch) fuse with and give rise to?

Fuses with Thyroid Gland to give rise to Parafollicular Cells

The Thymic Primordium develops from PA 3 endoderm, comprised of ________ ________.

Epithelial Cords

Epithelial Cords have 3 functions, which are...

1) Grow into surrounding mesenchyme -- Thymic Lobules 2) Become arranged around a central point -- forming Thymic Corpuscles 3) Form an epithelial reticulum for housing lymphocytes

This is not an arch derivative, and is the first endocrine gland to develop.

Thyroid Primordium (becomes Thyroid Gland)

This forms from a median endodermal thickening in the floor of the primordial pharynx.

Thyroid Gland

In Thyroid Gland development, it descends in the neck with ________ growth and passes ventral to the developing ________ bone and laryngeal cartilages.

Tongue | Hyoid

In Thyroid Gland development, it is connected to the tongue by a narrow tube called the...

Thyroglossal Duct

The Thyroglossal Duct (between tongue and thyroid gland) will eventually disintegrate, and the remainder of the duct is called the...

Foramen Cecum

This results from the insufficient migration of NCC into the 1st arch during the 4th week, making the arch have abnormal development. It causes malformation of the eyes, ears, mandible, and palate.

First Pharyngeal Arch Syndrome

This is another disease caused by defects in the 1st arch. It presents with malar hypoplasia with down-slanting palpebral fissures, defects of lower eyelids, deformed external ears, and sometimes middle and internal ears. It is Autosomal dominant.

Treacher-Collins Syndrome (mandibulofacial dysostosis)

Explain how Treacher-Collins Syndrome is caused.

There is a mutation in the TCOF1 gene (Treacher Collins-Franceschetti Syndrome 1), which encodes for the protein TREACLE. This protein is important for ribosome biogenesis. The protein is truncated and this leads to increased apoptosis of cranial NCC.

This is another disease caused by defects in the 1st arch. It typically occurs de novo in most patients, and is associated with hypoplasia of the mandible, cleft palate, and defects of the eyes and ears. Problems with NCC migration.

Pierre Robin Sequence

In Pierre Robin Sequence, the initiating defect is a small mandible (micrognathia). This results in posterior displacement of the ________, which causes obstruction of full closure of the palate. This results in bilateral _______ _______.

Tongue | Cleft Palate

This is the absence of a thyroid gland or one of its lobes (rare).

Agenesis of Thyroid Gland

This is the unilateral failure of thyroid gland formation. The left lobe is more commonly absent. Mutations in the receptor for thyroid-stimulating hormone (TSH) are likely involved.

Thyroid Hemiagenesis

This disease is caused from a chromosomal deletion. There is a breakdown of signaling from pharyngeal arch endoderm to NCC. Results in agenesis of thymus and parathyroid glands, as well as congenital hypoparathyroidism.

DiGeorge Syndrome

What disease is being described? - - Shortened philtrum of upper lip - - Low-set and notched ears - - Nasal Clefts - - Thyroid Hypoplasia - - Cardiac abnormalities (defects of aortic arch and heart) - - Congenital Hypoparathyroidism

DiGeorge Syndrome