The Pharyngeal Apparatus Flashcards
Lateral view of an embryo: What are the 3 bulges next to the Frontal prominence?
The 3 pharyngeal arches
What’s the origin of the neural crest cells?
- Neuroectoderm (1st stem in nervous system development = brain and spinal cord)
Neurulation process: Neural crest cells delaminate from overlying ectoderm and migrate to the peripheries and pharnygeal arches
What are the derivatives or Neural crests?
- CT and bones of the face and skull
- Cranial nerve ganglia
- C Cells of the thyroid gland
- Odontoblasts
- Dermis in face and neck
- Spinal (dorsal root) ganglia
What’s a Pharyngeal Apparatus?
Consists of paired:
- Pharyngeal arches
- Pharyngeal pouches
- Pharyngeal grooves
- Pharyngeal membranes
- What’s a Pharyngeal arch?
- Series of externally visible anterior tissue bands lying under the early brain (1/2/3/4/6)
Each arch has:
- A mesenchymal core (mesoderm & neural crest)
- A membrane (endoderm and ectoderm)
- External cleft (ectoderm)
- Mesenchymal core contains: Blood vessel/nerve/muscular cells/cartilage
What are the cranial nerves associated with the pharyngeal arch?
Arch 1: CN V (Trigeminal)
Arch 2: CN VII (Facial)
Arch 3: CN IX (glossopharyngeal)
Arch 4: CN X (Superior laryngeal branch of vagus)
Arch 6: (Recurrent laryngeal branch of vagus)
At the start of embryonic development, how many arches are there?
6
What happens to the 5th arch?
- Regresses soon after forming
What happens to the 1st Pharyngeal arch (mandibular arch)?
- Associated with the 1st aortic arch; develops into part of the maxillary artery
- Innervated by the TRIGEMINAL NERVE (CN V)
- Splits into an upper MAXILLARY PROMINENCE and a lower MANDIBULAR PROMINENCE
What are the derivatives of the 1st arch (somitomeric mesoderm)?
Somitomeric mesoderm:
- Artery: Terminal portion of the Maxillary artery (branch of the external carotid)
- Muscle (Max. prom):
+ None
- Muscle (Mand. prom): \+ Muscles of mastication \+ Mylohyoid \+ Ant belly of digastric \+ Tensor veli palatini \+ Tensor tympani
What are the derivatives of the 1st arch (Neural Crest)?
Neural Crest:
Bone or Cartilage: - Maxillary Prom (dorsal portion): \+ Maxilla \+ Zygomatic bone \+ Squamous temporal bone \+ Palatine bone \+ Vomer
- Mandibular Prom (ventral portion): \+ Mandible \+ Incus \+ Malleus \+ Associated with Meckel's cartilage
What happens to the 2nd Pharyngeal arch (hyoid arch)?
- Associated with the 2nd aortic arch; develops into the STAPEDIAL ARTERY
- Innervated by FACIAL NERVE (CN VII)
What are the derivatives of the 2nd arch (somitomeric mesoderm)?
Somitomeric Mesoderm:
- Artery:
+ Stapedial artery
+ Hyoid artery
- Muscles: \+ Muscles of facial expression \+ Posterior belly of digastric \+ Stylohyoid muscle \+ Stapedius
What are the derivatives of the 2nd arch (Neural Crest)?
Neural Crest:
- Bone or Cartilage (Reichert's)/: \+ Lesser horn of hyoid \+ Upper half of body of hyoid \+ Stapes \+ Styloid process
What happens to the 3rd Pharyngeal arch?
- Associated with aortic arch 3 which contributes to the COMMON CAROTID ARTERY and PROXIMAL SEGMENT OF INTERNAL CAROTID ARTERY
- Innervated by Glossopharyngeal nerve (CN IX)
What are the derivatives of the 3rd arch (somitomeric mesoderm)?
Somitomeric mesoderm:
Artery:
- Common carotid
- Proximal interal carotid
Muscle:
- Stylopharyngeus
What are the derivatives of the 3rd arch (Neural Crest)?
Neural Crest:
Bone or Cartilage:
- Greater horn of hyoid
- Lower half of body of hyoid
What happens to the 4th Pharyngeal arch?
- Associated with aortic arch 4; contributes to PROXIMAL SEGMENT OF RIGHT SUBCLAVIAN ARTERY and ARCH OF AORTA
- Innervated by SUPERIOR LARYNGEAL BRANCH OF VAGUS NERVE
What are the derivatives of the 4th arch (somitomeric mesoderm)?
Somitomeric mesoderm:
Artery:
- Proximal right subclavian
- Arch of aorta
Muscle:
- Muscles of soft palate (except tensor veli palatini)
- Muscles of the pharynx (except stylopharyngeus)
- Cricothyroid
- Cricopharyngeus
What are the derivatives of the 4th arch (Neural Crest)?
Neural Cest:
Bone or cartilage:
- Thyroid cartilage
- Cricoid cartilage
- Arytenoid cartilage
- Corniculate cartilage
- Cuneiform cartilage
(4th and 6th arches contribute to these Laryngeal cartilages)
What happens to the 6th Pharyngeal arch?
- Associated with aortic arch 6; contributes to proximal segments of pulmonary arteries & ductus arteriosus (becomes ligamentum arteriosum)
- Innervated by RECURRENT LARYNGEAL BRANCH OF VAGUS NERVE
What are the derivatives of the 6th arch (somitomeric mesoderm)?
Somitomeric mesoderm:
Artery:
- Ductus arteriosus
- Proximal pulmonaries
Muscles:
- Intrinsic laryngeal muscles (EXCEPT CRICOTHYROID)
- Skeletal muscle of esophagus
What are the derivatives of the 6th arch (Neural Crest)?
Neural Crests:
Bone or Cartilage:
- Thyroid cartilage
- Cricoid cartilage
- Arytenoid cartilage
- Corniculate cartilage
- Cuneiform cartilage
(4th and 6th arches contribute to these Laryngeal cartilages)
What are the Pharyngeal pouches?
- Endodermal-lined pockets that form on the inside of the pharynx between the arches
What happens to the 1st Pharyngeal Pouch?
- Develops into the AUDITORY TUBE & MIDDLE EAR CAVITY
- Expands to form the Tubotympanic recess = tympanic cavity + auditory tube & mastoid antrum
- Comes into contact with the 1st groove which forms the EXTERNAL AUDITORY MEATUS
What happens to the 2nd Pharyngeal Pouch?
- Epithelial lining of the pouch invade the surrounding mesenchyme; forming numerous infoldings that become the CRYPTS OF THE PALATINE TONSIL (PREMORDIUM OF THE PALATINE TONSIL)
- Later, lymphocytes infiltrate the underlying lamina propria to establish the definitive PALATINE TONSIL
- Part of the pouch remains as TONSILLAR SINUS OR FOSSA
What happens to the 3rd Pharyngeal Pouch?
- Divides into a superior (DORSAL) and inferior (VENTRAL) portion
Dorsal:
+ Forms the INFERIOR PARATHYROID GLAND - chief and oxyphil cells are derived from the endodermal lining of the pouch
Ventral:
+ Forms the THYMUS
- The epithelial reticular cells are derived from the endodermal lining of the pouch
- T cell progenitors from bone marrow infiltrate the cortex to ESTABLISH DEFINITIVE THYMUS
- Primordia of THYMUS & PARATHYROID LOSE THEIR CONNECTIONS WITH PHARYNX and MIGRATE INTO NECK (anterior mediastinum)
What happens to the 4th Pharyngeal Pouch?
- Divides into a DORSAL and VENTRAL portion?
Dorsal:
- Contributes to the SUPERIOR PARATHYROID GLANDS
Ventral:
- Forms a diverticulum (outpouching of a hollow tube) called ULTIMOBRANCHIAL BODY, the cells of which migrate into the thyroid and differentiate into PARAFOLLICULAR CELLS of the THYROID GLAND
Anomalous development of the derivatives of pouch 3 and/or 4 can result in?
Ectopic or absent of:
+ Parathyroid
+ Thymic
+ Parafollicular thyroid tissue
What’s DiGeorge syndrome?
- Disorder caused by deletion of the long arm of chromosome 22
- Results in hypoplasia of 2nd and 3rd pharyngeal pouch derivatives
What are the symptoms of DiGeorge syndrome?
- Hypoplasia of the hyoid
- Thymic hypoplasia (immunodeficiency due to lack of T-cells)
- Hypoparathyroidism (missing or hypoplastic inferior parathyroid glands)
What can Hypoplasia of the 2nd and 3rd arches cause?
- 1st arch disruption, leading to:
+ Micrognathia (reduced jaw)
+ Cleft palate
+ Hearing loss
What are the Pharyngeal clefts?
- Ectodermal-lined recesses that appear on the OUTSIDE of the Pharynx between the arches (Cleft 1 is between Arch 1 & 2; etc)
What happens to the 1st Pharyngeal cleft?
- Develops into the EXTERNAL AUDITORY MEATUS (remember, corresponding pouch develops into the auditory tube and the intervening membrane develops into the tympanic membrane)
- Defects in this can result in PREAURICULAR CYSTS and/or FISTULAS
What happens to the 2-4 Pharyngeal clefts?
- Overgrown by expansion of the 2nd pharyngeal arch and are usually obliterated
- Remnants can appear along the anterior border of the sternocleidomastoid muscle in the form of cervical cysts or fistulas
What’s the Thyroid gland?
- 1st endocrine gland to develop (day 24)
- Makes 2 hormones:
+ Thyroxine (T4)
+ Triiodothyronine (T3) - Influences cellular metabolism
Outline the development of the Thyroid gland?
- NOT DERIVED FROM A PHARYNGEAL POUCH
- Develops from the median endodermal thickening in the floor of the primordial pharynx; these cells differentiate into the FOLLICULAR CELLS of the THYROID GLAND
- ENDODERMAL CELLS OF the ULTIMOBRANCHIAL BODY migrate into the gland and give rise to the PARAFOLLICULAR CELLS of the THYROID
- Differential growth of the embryo leads to DIVERTICULUM ELONGATION, but remains connected to the forming tongue by the THYROGLOSSAL DUCT (later obliterated)
- Site of the opening of the THYROGLOSSAL DUCT IS the FORAMEN CECUM which is found in the midline at the TERMINAL SULCUS OF THE TONGUE
What are the anomalies of the Thyroid gland?
- Can result in ECTOPIC THYROID TISSUE and/or CYSTS present along the course of the THYROGLOSSAL DUCT
- Abnormal shape = Pyramidal lobe
- Anomalies of position = Lingual thyroid
How does the Anterior 2/3 of the tongue develop? (incl innervation)
- Anterior 2/3 derived from median (tuberculum impar) and lateral lingual swellings develop on each side of the median tongue buds that arise from the floor of the 1st pharyngeal arch
- Distal tongue buds increase in size, merge together and overgrow the median bud to form the anterior 2/3rd of the tongue
- The median tongue bud DOES NOT form any part of the adult tongue
- CT and vasculature: derived from arch masenchyme
Innervation:
- Sensory of mucosa: Lingual branch of trigeminal nerve
- Taste: Chorda tympani branch of facial nerve
- Motor of intrinsic skeletal muscle: Hypoglossal nerve
How does the Posterior 1/3 of the tongue develop? (incl innervation)
- Appearance of Copula due to fusion of Ventromedial part of 2nd pair of arches
- Hypopharyngeal eminence (prominence) appears due to proliferation of mesenchyme from 3rd & 4th pharyngeal arches
- Hypopharyngeal eminence overgrows the Copula
- Posterior 1/3 of the tongue develops from the rostral part of the Hypopharyngeal eminence
(POSTERIOR 1/3 OF TONGUE IS DERIVED FROM 3+4TH ARCH - NO CONTRIBUTION FROM 2ND ARCH)
Innervation:
+ Sensory of mucosa: Mostly glossopharyngeal + some vagus
+ Taste: Mostly glossopharyngeal + some vagus
+ Motor of intrinsic skeletal muscle: Hypoglossal
Development of the tongue: When do the Papillae and Taste buds appear?
- End of week 8
- Taste buds develop during week 11 to 13 - via inductive interaction between epithelial cells and invading gustatory nerve
What’s 1st arch syndrome?
x2 types:
- Treacher Collins Syndrome - caused by autosomal dominant gene - underdevelopment of zygomatic bond and defective eyelids and ears
Pierre Robin Syndrome - underdevelopment of mandible - cleft palate and defects of the eye and ear
