9. pharyngeal apparatus

PHARYNGEAL APPARATUS

• Pharyngeal apparatus consists of, 1.Pharyngeal arches – 6 pairs 2.Pharyngeal pouches – 5 pairs 3.Pharyngeal grooves – 4 pairs 4.Pharyngeal membranes – 4 pairs

Pharyngeal apparatus

Pharyngeal arches

• 6 pairs of pharyngeal arches are developed.• Pharyngeal arches are formed from Paraxial

mesoderm, lateral plate mesoderm and neural crest cells.

• Arches are covered by ectoderm externally and by endoderm internally.

Mesoderm

1. Notochord2. Intermediate zone of neural crest3. Neural groove4. Neural crest5. Neural fold6. Dorsal root ganglion7. Neural tube8. Surface ectoderm

1st Pharyngeal arch (Mandibular arch)

Muscles :Muscles of mastication (Temporalis, Masseter & Pterygoids), Mylohyoid muscle, Tensor veli palatani, Tensor tympani & Anterior belly of digastric.

Nerve: Trigeminal nerve (Vth). Bones: Maxilla, zygomatic bone, Temporal bone,

Mandible, Incus, malleus. Ligament: Sphenomandibular ligament.

2nd Pharyngeal(Hyoid) arch

Muscles: Muscles of facial expression (Buccinator, Auricularis, Frontalis, Platysma, Orbicularis oris, Orbicularis oculi), Posterior belly of Digastric, Stylohyoid, Stapedius muscle.

Nerve: Facial nerve(VIIth). Bones: Lesser horn and upper body of Hyoid,

Stapes, Styloid process. Ligament: Stylohyoid ligament.

3rd Pharyngeal arch

Muscles: Stylopharyngeus muscle.Nerve: Glassopharyngeal nerve (IXth)Bones: Greater horn &lower body of

Hyoid.

4th Pharyngeal arch

Muscles: Muscles of soft palate (except tensor veli palatani), Muscles of pharynx (except stylophangeus), Cricothyroid, Cricopharynx.

Nerve: Superior laryngeal branch of Vagus nerve.

5th Pharyngeal arch

• Regresses.

6th Pharyngeal arch

• Muscles: Intrinsic muscles of larynx (except cricothyroid), Muscles of upper esophagus.

• Nerve: Recurrent laryngeal nerve of Vagus nerve.

• Laryngeal cartilages.

Derivatives of Pharyngeal arches Nerves Bones Muscles

1st Arch Trigeminal (Vth) Maxilla, Mandible, Temporal, Malleus, incus.

Muscles of mastication

2nd Arch Facial (VIIth) Lesser horn and upper body of Hyoid, Stapes, Styloid process

Muscles of facial expression.

3rd Arch Glassopharyngeal (IXth)

Greater horn &lower body of Hyoid.

Stylopharyngeus muscle

4th Arch Superior laryngeal branch of Vagus (Xth)

- Muscles of soft palate , Muscles of pharynx

5th Arch - - -

6th Arch Recurrent laryngeal branch of Vagus (Xth)

Laryngeal cartilages

Intrinsic muscles of larynx ,Muscles of upper esophagus.

Pharyngeal pouches

1st Pouch Epithelial lining of Auditory tube & Middle ear cavity. 2ndPouch Epithelial lining of Palatine tonsil crypts. 3rd Pouch Inferior parathyroid gland. Thymus. 4th Pouch Superior Parathyroid gland . Ultimo bronchial body (Parafollicular

cells of Thyroid)

Derivatives of Pharyngeal pouches

Pharyngeal grooves(clefts)

1st cleft External auditory meatus. 2nd ,3rd &4th clefts Obliterates.

Pharyngeal membranes

• 1ST Pharyngeal membrane Tympanic membrane.

Clinical condition

Digeorge syndrome Absence development of Parathyroid glands

and thymus from 3rd &4th Pharyngeal pouches.

Clinical: 1.Primary hypoparathyroidism- Hypocalcemia 2.Severe recurrent infections.

Associations : Micrognathia, Hypertelorism,Low set ears,congenital heart defects (Persistant truncus arteriosus &Interrupted aortic arch).

Clinical condition

1st Arch syndrome Abnormal development of derivatives of 1st

pharyngeal arch, due to insufficient migration of neural crest cells into 1st arch.

1.Treacher collins syndrome: Malar (Zygomatic bone) Hypoplasia, Downslanting of palpebral fissures, defects of lower eyelids, deformed external ears.

2.Pierre Robin syndrome: Hypoplasia of Mandible, Cleft palate, defects of eyes &ears.

Clinical condition

• Congenital auricular sinuses & cysts: Sinuses and cysts formed in front of

external ears . Formed by 1st Pharyngeal groove

(Ectodermal cells).

Clinical condition

• External Branchial sinuses: External openings present on side of the neck, due to failure of obliteration of 2nd ,3rd &4th Pharyngeal grooves or Pharyngeal clefts.

• Internal Branchial sinuses: Internal openings present in pharynx due to persistence of proximal part of 2nd Pharyngeal pouch.

Obliteration of grooves

Branchial sinuses

Branchial sinuses &cysts

Clinical condition

Branchial fistula Abnormal canal that opens internally

into tonsillar sinus in pharynx and externally on the side of the neck.

Defect: Failure of obliteration of 2nd , 3rd &4th Pharyngeal grooves and Persistence of proximal part of 2nd pharyngeal pouch.

Branchial fistula

Clinical condition

Branchial cyst Fluid filled mass formed due to persistence

of 2nd ,3rd & 4th Pharyngeal grooves. Location: Below the angle of the jaw & along

the anterior border of the SCM. Some times associated with Branchial

sinuses.

Obliteration of grooves

Branchial cyst

Migration of Thymus &Inferior Parathyroids

Clinical conditions

• Accessory Thymus : mass of extra thymus present in neck ,close to inferior parathyroid. It is separated thymus tissue from Thymus gland during its migration to mediastinum.

• Ectopic Parathyroid gland: Abnormal position of parathyroid glands. Present at bifurcation of common carotid artery or near thymus.

Accessory thymus & Ectopic Parathyroids

Development of Thyroid

• Develops from floor of the pharynx.• A small pouch of endodermal cells called as Thyroid

primordium, develops from floor of pharynx.• Developing thyroid descends down in neck. During

descent a duct called Thyroglossal duct formed between descending thyroid and floor of pharynx.

• After descent, thyrogossal duct regresses.• A pit present in tongue called Foramen cecum ,

represents the site from which thyroid developed.

• Thyroid consists of two lobes connected by Isthamus of thyroid. A small lobe called Pyramidal lobe present above isthamus.

Development of thyroid

Thyroglossal duct &Descent of thyroid

Clinical condition

ThyroglossaI cyst &sinuses Cyst formed from abnormal

persistence of Thyroglossal duct.Cyst present in midline of anterior neck.

If the thyroglossal cyst opens outside in midline of anterior neck,it is called as Thyroglossal sinus.

Sites of Thyroglossal duct cysts

Thyroglossal duct cyst

Clinical conditions

• Ectopic thyroid: Abnormal location,present at any site along path of its descent.Lingual thyroid and Sublingual thyroids.Ectopic thyroid is due to absence of descend.

• Accessory thyroid:Extra thyroid tissue , present in thymus or at any site of descend.

• Agenesis of Thyroid: Absence of development of lobes of thyroid.

Development of Tongue

Pharyngeal arch mesoderm Connective tissue,Blood vessels &Nerves (except Hypoglossal nerve).

Occipital myotomes Muscles of Tongue &Hypoglossal nerve (XII).

Anterior 2/3rd of tongue: Derived from 1st Pharyngeal arch

mesoderm. 1st arch Median lingual swelling

(Tuberculum impair) -1 Lateral lingual swellings-2 Sensory Nerve supply: Lingual branch of the

Mandibular division of Trigeminal nerve (V).

Development of the tongue

• Median sulcus of the tongue: sulcus formed in the median plane due to fusion of two Lateral lingual swellings.

• Lingual septum:Fibrous septum present between two halves of anterior 2/3rd of tongue.

• Nerve supply to taste buds of anterior 2/3rd is by Chorda tympani of Facial nerve (VII)

Posterior 1/3rd of the tongue: 2nd Pharyngeal arch Copula 3rd Pharyngeal arches Hypopharyngeal or

Hypobranchial eminence. Sensory& taste nerve supply :Glossopharyngeal

nerve

Terminal sulcus : “V” Shaped Sulcus present between anterior 2/3rd and posterior 1/3rd.

Posterior end of tongue

• 4th Pharyngeal arch Epiglottis &Extreme posterior end of tongue.

• Sensory nerve supply : Superior laryngeal branch of Vagus nerve.

Nerve supply of the tongue• Anterior 2/3rd :General sensation –

Mandibular branch of Trigeminal nerve (V) Taste – Chorda tympani of

Facial nerve( except vallate papillae-IX) • Posterior 1/3rd : Glassopharyngeal nerve• Muscles of Tongue :Hypoglossal nerve (Except

Palatoglossus – Vagus nerve (X) )

Clinical conditions

• Congenital lingual cysts &fistulas: Formed by persistence of parts of Thyrogossal duct.Causes difficult in swallowing.

• Ankyloglossia (Tongue-tie):Frenulum extends upto the tip of the tongue & attaches tongue to floor of oral cavity.

• Macroglossia:Big tongue.Due to Lymphangioma or Muscular hypertrophy.

• Microglossia • Bifid tongue: Due to incomplete fusion of two lateral

lingual swellings.

Ankyloglossia (Tongue-tie)

Development of Face

• Face is formed by neural crest derived mesenchyme prominences,

Frontonasal prominence -1 Maxillary prominences-2 Medial nasal prominences -2 Lateral nasal prominences-2 Mandibular prominence -2

Development of face

Development of face

• Frontonasal prominence Forehead,Bridge of the nose.

• Maxillary prominences Cheeks ,Lateral portions of upper lip.

• Medial nasal prominences Upper lip,tip of the nose.

• Lateral nasal prominences Alae of the nose.• Mandibular prominences Lower lip.

Clinical condition

Cleft lip• Defect : Failure of fusion of Median nasal

prominences with maxillary prominences.

Development of Palate

Primary palate : Develops from Median palatine

process. (derived from Medial nasal prominences) Secondary palate: Develops from Lateral palatine processes or Palatal shelves.(derived from Maxillary prominences)

secondary palate unites with nasal septum &Primary palate and forms Palate. Median line formed on palate due to fusion of Palatine shelves is called Median palatine raphe.

Palate

Development of palate

Clinical condition

Cleft palateDefect: Failure of fusion of two palatine shelves

(Lateral palatine processes or Maxillary promineces)

or Failure of fusion of palatine shelves or

lateral palatine processes(secondary palate) with Median palatine process (primary palate)

Cleft lip &Cleft palate

Development of palate

• Cleft lip &cleft palate are associated with, Drugs - Phenytoin, Carbamazepine, Valproate. Genetical diseases- Patau syndrome

(Trisomy13)

Salivary glands

• Parenchymal or glandular part develops from ectodermal lining (except sublingual) of oral cavity.

• Connective tissue part of glands derived from Neural crest cells. 1. Parotid glands

2. Submandibular glands 3. Sublingual glands.- develops from

endoderm.