Pharyngeal arches
Tongue development and malformations
Salivary glands development
19. 5. 2021
Jan Křivánek
https://www.youtube.com/watch?v=oP1-ejJdZyc
Pharyngeal arches
Phylogenetically conserved organ, serves as a carrier for gills (which work as a respiratory organ)
First appears in sharks, around the pharyngeal gut
In vertebrates, transforms and forms the basis of important organs - branchiogenic organs
Wiki
The pharyngeal apparatus starts to develop in human embryos in the neck region behind the frontal (frontonasal)
prominence in the second half of the 4th week
Pharyngeal arches 6
Pharyngeal pouches (entodermal) 5
Pharyngeal clefts (grooves) (ectodermal) 4
Membranae obturantes 4
All structures are paired
Pharyngeal arches
Pharyngeal (branchial) arches (6)
The first four - cause a obvious segmented structure of the neck (5th
and 6th are rudimentary)
Cells of the mesencephalic and rhombencephalic part of neural crest
migrate into the paraaxial mesoderm of the first cervical somites and
contribute to formation on arches and subsequently organs
The formation of pharyngeal arches is controlled by the endoderm of
the pharyngeal arches
Ectomesenchymal derivatives: ligaments, cartilages, bones
Paraaxial mesoderm derivatives: muscles of pharyngeal arches and
branchial arteries
Migration of neural crest (ectomesenchyme) in several
migratory pathways
Controled by Hox genes which regulate expression of
transcription factors with effectory function
Pharyngeal pouches - 5
The first starts to develop on the stage of 5 somites
The 5th is rudimentary and develops as a part of the fourth pouch at end of the 1st month
Endodermal origin
Pharyngeal clefts - 4
They have the form of shallow grooves
ectoderm origin
Membranae obturantes - 4
Two-layer memranes that separate each ectoderm and entoderm groove (physiologically do not perforate in humans)
Frontal section through apparatus and branchial arch components
In each arch is: Cartilage
Skeletal muscle basis (mezoderm)
Arch artery
Branchial arch nerve
1. Pharyngeal arch (mandibular)
arch cartilage (Meckel´s cartilage) - malleus, incus, lig. mallei ant., sphenomandibulare lig.
muscles of mastication, mylohyoid and anterior belly of digastric, tensor tympani, tensor veli palatini
the 1st aortic arch - disappears (a small portion may persist and form maxillary artery)
the 1st branchial nerve - trigeminal
Derivatives of
pharyngeal
arches
2. Pharyngeal arch (hyoid):
arch cartilage (Reichert´s cartilage) - stapes, styloid process, lesser cornu of hyoid, upper part of body of the hyoid bone
muscles of facial expressions, stapedial and stylohyoid muscle, posterior belly of digastric
the 2nd aortic arch - disappears (small portions of this arch contributes to the hyoid and stapedial arteries)
the 2nd branchial nerve - facial
Derivatives of
pharyngeal
arches
3. Pharyngeal arch
arch cartilage - greater cornu of hyoid, lower part of body of the
hyoid cartilage
stylopharyngeus muscle
the 3rd aortic arch - has the same fate on the right and left sides
and forms the first part
of the internal carotid artery
the 3rd branchial nerve - glossopharyngeal
4. - 6. Pharyngeal arch
arch cartilages - laryngeal cartilages and tracheal rings
cricothyroid, levator veli palatini, constrictors of pharynx, intrinsic muscle of
larynx
the 4th aortic arch - gives rise on left: a part of the aortic arch between left
common carotid a left subclavian arteries; on the right: the proximal segment
of the subclavian artery
the 5th aortic arch - transient and obliterates
the 6th aortic arch - transformed into the pulmonary artery (their branches)
branchial nerves - vagus nerve /superior laryngeal, branch of vagus (from the 4th),
recurrent laryngeal branch of vagus (from the 6th)
Derivatives of
pharyngeal
arches
Transformation of cartilages of pharyngeal arches
(summary)
the 1st aortic arch – disappears (a small portion can persist to form short piece of the maxillary artery)
the 2nd aortic arch – disappears (small portions of this arch contributes to the hyoid and stapedial arteries)
the 3rd aortic arch – has the same development on the right and left side, it gives rise to the initial portion of the
internal carotid artery
(the continuation of its trunk is formed by the cranial portion of the dorsal aorta + primitive internal carotid)
the external carotid derives from
the cranial portion of the ventral aorta
the common carotid corresponds to a
portion of the ventral aorta between
exits of the third and fourth arches
Transformations of aortic arches (summary)
the 4th aortic arch - has ultimate fate different on the right and left side:
Left: forms part of the arch of the aorta between left common carotid and left subclavian artery
Right: forms the proximal segment of the right subclavian artery
the 5th aortic arch - is transient and soon obliterates
the 6th aortic arch - pulmonary arch - the proximal part transforms into the right branch of the pulmonary artery and
the distal part disappears
On the left side, the distal part persists as the ductus arteriosus during intrauterine life
The proximal part gives rise to the left branch of the pulmonary artery
Summary
Functional future has only the
1. pouch
2. - 4. obliterates and form a
sinus cervicalis
Pharyngeal clefts (ectodermal)
Derivatives of pharyngeal pouches 1. Cavum tympani and Eustachian tube
2. Fossa tonsilaris
3. Epithelial reticulum of thymus and gl. parathyr. inf.
4. gl. parathyroidea sup. + ultimobranchial body
5. rudimentary
Defects caused by maldifferentiation of the pharyngeal
apparatus
1. Branchial (cervical) cysts
2. Branchial (cervical) fistulae
3. Branchial (cervical) vestiges (rudiments of branchial arches)
4. Preauricular cysts a fistulae
5. Syndrome of the 1. branchial arch
6. DiGeorge syndrome
7. Ectopia of thymus
Branchial cysts (lateral neck cysts)
Origin from persisting sinus cervicalis, positioned under angulus mandibulae
Subcutaneously or deep around the pharynx (possibly larynx)
When a cyst ruptures, communication occurs with the body surface or pharynx
Lined with stratified squamous epithelium
They may contain a liquid content with cholesterol crystals
Usually clinically not important
https://subent.com/removal-of-branchial-cleft-cyst
Abnormal communication of the pharyngeal cavity with the body surface
They arise when the membranae obturantes obliterate
Between 2. pouch and cleft
(fossa tonsillaris - sternocleidomatoideus muscle)
Between 3. pouch and cleft
(tongue - art. sternoclavicularis)
Complete
at the outlet on the skin
Incomplete
external, internal
Branchial fistula (lateral cervical fistula)
Koltsidopoulos et Skoulakis, CMAJ, 2018
Small grooves, pits or cysts in skin
in triangular area anteriorly to the
pinna (auricle)
Origin: by persistence of sulci
separating auricular hillocks
Residues of some components of the pharyngeal arches, usually cartilage.
Occurrence: in the subcutaneous ligament of the neck above the lower 1/3 m.sternocleidomastoid
Rare
Branchial vestiges (rudiments of branchial arches)
Preauricular cysts and fistulae
Isaacson, IJPO, 2019
Complex malformation of the skeleton of the face (both jaws, palate), eye and ear, caused by delay or non-migration of
crista neuralis into the 1st pharyngeal arch
Types:
1) Treacher-Collins syndrome - dysostosis mandibulofacialis – autosomal dominant hereditary malformation
anatomically: hypoplasia to aplasia of zygomatic bones, hypoplasia of the upper and lower jaw, macrostomy, gothic
floor, hypoplastic and sparse teeth, malocclusion - the face shows a characteristic physiognomy
The First pharyngeal arch syndrome
2) Pierre-Robin syndrom
Hypoplasia of the mandible, gothic floor or posterior cleft palate, glossoptosis, ear defects
Autosomal recessive inheritance, X chromosome - linked
The intellect of individuals is not affected
Symptoms: due to the shortened base of the oral cavity, individuals after birth have difficulty feeding and breathing
(stridor - caused by a disproportion between the lower jaw and the tongue)
Resnick et at, 2019
Agnathia
Incorrect development of the 1st pharyngeal arch. Caused by improper migration of neural crest cells.
Anatomically: hypoplasia of the mandible, shortened philtrum - nasal hypoplasia, congenital aplasia of the thymus and
parathyroid glands, hypoplasia of the thyroid gland, defects of the heart and large vessels (right aortic arch), external
ear defects
Clinically: hypoparathyroidism (hypocalcemic seizures), absence of cellular immunity, manifestations of heart defect
Incidence 1: 50 000
Etiology: Most frequently deletion on chromosome 22 - (22q11)
DiGeorge syndrome
Thymus ectopia
Ectopia = correctly developer organ/structure in
incorrect place
When thymus fails to descent: Cervical thymus - near
the lower pair of parathyroid glands
Accessory thymus
The development of the tongue begins in the 5th week at the interface of the stomodeum and the beginning of the primitive pharynx
Anterior 2/3 of the tongue Apex and corpus linguae Formed from the mandibular process of the 1st pharyngeal arch
Posterior 1/3 of the tongue Radix linguae Formed from the 3rd and 4th pharyngeal arch
Apex and corpus
On the mandibular prominence are 3 mesenchymal protrusions covered with ectoderm:
Paired tuberculum linguale laterale (dx et sin) - distal lingual protrusion
Middle unpaired tuberculum impar (tuberculum linguale mediale) - middle tongue protrusion - more caudally
Tongue development
Radix linguae
2 foundations: copula - fused ectomezenchyme of the ventral ends of the hyoid arch
eminentia hypobranchialis - formed by fusion of ventral ends of 3rd and 4th pharyngeal arch
both the copula and the hypobranchial eminence are covered by the endoderm
Endoderm between the tuberculum impar and the dome very intensively proliferates and grows caudally, its luminization creates a
ductus thyreoglossus (see thyroid gland)
During the 6th week, the protrusions begin to fuse together
Lateral protrusions enwrap the unpaired tuberculum impar - a uniform apex and corpus linguae is formed
In definitive proportions, it resembles the original symmetrical origin of the tip and body of the tongue sulcus medianus linguae
(+septum linguae)
Only a small part of the body near the root of the tongue comes from the tuberculum impar)
The hypobranchial process merges with copula and
moves forward - approaching the base of the
corpus with which it merges
Radix - Pharyngeal part of the tongue
The fusion line is visible until
adulthood as a shallow "V" - shaped
groove - Sulcus terminalis
At the top of the "V" is a short channel:
Foramen caecum, remnant of the
proximal end of the ductus
thyreoglossus
The ectoderm and entoderm of the common base of the tongue differentiate into stratified squamous epithelium, taste bud cells, and
secretory compartments and ducts of the tongue glands
From ectomezenchyme of fused protrusions, the ligament of the tongue, blood and lymph vessels develop, incl. lymphatic tissue of
the root of the tongue
Muscles of the tongue come from the occipital myotoms, which move to its base and merge together.
During the fusion of myotomes, their motor nerves also merge (segmental arrangement) - the hypoglossus nerve is formed
Development of tongue papillae - in the 8th week – firstly papillae vallatae, foliatae (near the branches of the n. IX.), fungiformes
(branches of the n. Lingualis), filiformes (the 11th-12th week)
Taste buds - weeks 11-13
Sensitive innervation: Apex and corpus - trigeminal nerve (n. mandibularis)
Radix - n. Glossopharyngeus
Innervation of taste buds:
- Taste buds in papillae fungiformes fungal - n. facialis - chorda tympani
- Taste buds in papillae foliatae and circumvallatae - n. glossopharyngeus
- Taste buds in another location (radix lingue, isthmus faucium) - n. vagus
Tongue development
At birth: the tongue occupies the oral cavity
Postnatally: the root of the tongue descends into the pharynx – process finished at the 4th year of life
Ankyloglossia (lingua accreta) - short frenulum, limited mobility of the tip of the tongue, it is not possible to stick out the tongue
(difficulty breastfeeding), 1: 300 births. The frenulum usually lengthens spontaneously (surgery is not needed)
Congenital lingual cysts and fistulas - persistence of ductus thyreoglossus – clinically usually non important, causes problems only
when enlarged (discomfort in the pharynx or dysphagia)
Macroglossia - a rare, abnormally large tongue (associated with some syndromes, e.g. Down sy.)
Microglossia - a rare, abnormally small tongue (mostly associated with micrognathia; microglossia in combination with limb defects Hanhart's
syndrome)
Glossoptosis - displacement of the tongue dorsally. Pushes on the epiglottis, narrowing of the pharynx.
Lingua bifida (lingua fissa, glossoschisis) - a very rare anomaly, incomplete fusion of the tubercula lingualia lateralia
complete cleft - including the tip of the tongue (associated with the cleft of the lower lip and jaw)
partial cleft - deep longitudinal groove (groove) in the body of the tongue
Aglossia – tongue not developed
Overview of tongue development defects
Salivary glands as derivatives of the lining of the stomodea or other structures: the oral side of the palate, the tip
(ectoderm) and the root of tongue and the oral base (entoderm)
ectoderm: small salivary glands of lips and face, palate, gl. apicis lingue and parotid gland
entoderm: Weber's and Ebner's glands of the tongue, gl. submandibularis and gl. sublingualis
They all develop in a similar way:
From the epithelium (ecto- or entoderm) at the site of the future gland(s): cells begin to proliferate against
adjacent ectomezenchyme
They lengthen and branch - the basis for the glandular duct system is created, the last 6th generation form terminal
branches
Development of salivary glands
At the ends of the terminal branches (6th-7th generation) clusters of small spherical clusters of cells are subsequently
formed - singular acins
The secretion starts during the 5th month of development, followed by gradual lumen formation during the 6th month
of development
During this period, the division of the parenchyma into lobules begins, and thin septa are formed in glandular
parenchyma from the superficial mesenchyme.
Lobulization continues until birth when glands become fully functional and begin to excrete saliva
Basis for gl. parotis 4th - 6th week, at the upper edge of both corners of the mouth; after narrowing
of the rima oris, the ductus parotideus opens into the vestibule on the buccal side
Basis for gl. submandibularis 6th week
Basis for gl. sublingualis 8th week
Small salivary glands during 3rd month of development
Development of salivary glands