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Questions and Answers
What is primarily derived from multipotent neural crest stem cells during the development of the pharyngeal arches?
What is primarily derived from multipotent neural crest stem cells during the development of the pharyngeal arches?
What is the source of endothelial cells in the pharyngeal arches?
What is the source of endothelial cells in the pharyngeal arches?
Which anatomical structures are primarily formed from the mesenchyme in the pharyngeal arches?
Which anatomical structures are primarily formed from the mesenchyme in the pharyngeal arches?
Which of the following is NOT a typical component of a pharyngeal arch?
Which of the following is NOT a typical component of a pharyngeal arch?
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How is the endothelium of the pharyngeal arches 3 to 6 primarily derived?
How is the endothelium of the pharyngeal arches 3 to 6 primarily derived?
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What are the main components of the pharyngeal apparatus?
What are the main components of the pharyngeal apparatus?
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At what developmental week do the pharyngeal arches begin to develop?
At what developmental week do the pharyngeal arches begin to develop?
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Which of the following structures does the maxillary prominence help form?
Which of the following structures does the maxillary prominence help form?
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Which pair of pharyngeal arches is associated with the formation of the hyoid bone?
Which pair of pharyngeal arches is associated with the formation of the hyoid bone?
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What is the consequence of the persistence of the oropharyngeal membrane?
What is the consequence of the persistence of the oropharyngeal membrane?
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How many pairs of pharyngeal arches are visible externally by the end of the fourth week?
How many pairs of pharyngeal arches are visible externally by the end of the fourth week?
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What type of tissue primarily makes up each pharyngeal arch?
What type of tissue primarily makes up each pharyngeal arch?
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What does the stomodeum represent in embryonic development?
What does the stomodeum represent in embryonic development?
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Which structure is specifically formed by the dorsal end of the first pharyngeal arch cartilage?
Which structure is specifically formed by the dorsal end of the first pharyngeal arch cartilage?
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What is the primary role of the first pharyngeal arch cartilage during development?
What is the primary role of the first pharyngeal arch cartilage during development?
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Which pharyngeal arch is responsible for the muscles of mastication?
Which pharyngeal arch is responsible for the muscles of mastication?
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From which pharyngeal arch does the intrinsic musculature of the larynx develop?
From which pharyngeal arch does the intrinsic musculature of the larynx develop?
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What does the stylohyoid ligament develop from?
What does the stylohyoid ligament develop from?
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What occurs during the fifth week of development regarding the second pharyngeal arch?
What occurs during the fifth week of development regarding the second pharyngeal arch?
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Which pharyngeal arch contributes to the formation of the stapes?
Which pharyngeal arch contributes to the formation of the stapes?
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The greater cornu of the hyoid bone is derived from which pharyngeal arch?
The greater cornu of the hyoid bone is derived from which pharyngeal arch?
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What is a characteristic of the fifth pharyngeal arch?
What is a characteristic of the fifth pharyngeal arch?
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Which cranial nerve is responsible for the major sensory innervation of the face?
Which cranial nerve is responsible for the major sensory innervation of the face?
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Which pharyngeal pouch contributes to the formation of the tympanic membrane?
Which pharyngeal pouch contributes to the formation of the tympanic membrane?
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Which cranial nerves innervate the second to sixth pharyngeal arches?
Which cranial nerves innervate the second to sixth pharyngeal arches?
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What is the primary function of the trigeminal nerve regarding the muscles it innervates?
What is the primary function of the trigeminal nerve regarding the muscles it innervates?
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What anatomical area is derived from the mesenchyme of the pharyngeal arches?
What anatomical area is derived from the mesenchyme of the pharyngeal arches?
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Which nerves primarily supply innervation to the fourth pharyngeal arch?
Which nerves primarily supply innervation to the fourth pharyngeal arch?
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How many pairs of pharyngeal pouches are well defined during development?
How many pairs of pharyngeal pouches are well defined during development?
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What develops as an outpouching of the endoderm between the pharyngeal arches?
What develops as an outpouching of the endoderm between the pharyngeal arches?
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What structure is primarily formed by the second pharyngeal pouch during its development?
What structure is primarily formed by the second pharyngeal pouch during its development?
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At what stage does initial lymphoid cell infiltration into the palatine tonsil occur?
At what stage does initial lymphoid cell infiltration into the palatine tonsil occur?
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Which pharyngeal pouch forms the inferior parathyroid glands?
Which pharyngeal pouch forms the inferior parathyroid glands?
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What is the first cleft that persists into postnatal structures?
What is the first cleft that persists into postnatal structures?
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What is the developmental result of the merging of medial nasal and maxillary prominences?
What is the developmental result of the merging of medial nasal and maxillary prominences?
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What major anomaly is characterized by absence of thymus and parathyroid glands at birth?
What major anomaly is characterized by absence of thymus and parathyroid glands at birth?
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Which embryonic structure primarily contributes to the eyes during development?
Which embryonic structure primarily contributes to the eyes during development?
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What congenital condition is characterized by a failure of mesenchymal tissue to merge properly, leading to defects in the mouth, ears, and mandible?
What congenital condition is characterized by a failure of mesenchymal tissue to merge properly, leading to defects in the mouth, ears, and mandible?
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What structure do cervical sinuses result from?
What structure do cervical sinuses result from?
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What forms as a result of the failure to canalize the nasolacrimal duct?
What forms as a result of the failure to canalize the nasolacrimal duct?
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Which structure develops from remnants of the second pharyngeal pouch?
Which structure develops from remnants of the second pharyngeal pouch?
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What can contribute to the development of cleft lip and palate?
What can contribute to the development of cleft lip and palate?
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What is the characteristic orientation of the orbits at the end of facial development?
What is the characteristic orientation of the orbits at the end of facial development?
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Study Notes
Development of Pharyngeal Apparatus, Head and Face
- The pharyngeal apparatus comprises pharyngeal arches, pouches, grooves, and membranes
- These embryonic structures contribute to face and neck development
Pharyngeal Arches
- Pharyngeal arches begin to develop in the fourth week
- Neural crest cells migrate to the head and neck region
- The first arch, the primordial jaws, appears as surface elevations lateral to the developing pharynx
- Additional arches form as ridges on either side of the future head and neck
- By the end of the fourth week, four pairs of arches are visible externally
- The fifth and sixth arches are rudimentary and not visible externally
Separation of Pharyngeal Arches
- Pharyngeal arches are separated by pharyngeal grooves (clefts)
- Grooves are numbered in a craniocaudal sequence
- The first arch separates into maxillary and mandibular prominences
- The maxillary prominence forms the maxilla and part of the vomer bone
- The mandibular prominence forms the mandible and squamous temporal bone
- The second arch contributes to the formation of the hyoid bone, along with the third arch
Pharyngeal Arch Components
- Each arch consists of a core of mesenchyme
- The mesenchyme is covered by ectoderm externally and endoderm internally
- Most mesenchyme derives from neural crest cells that migrate into the arches during the fourth week
- Myogenic mesoderm from paraxial regions moves into each arch, forming a central core of muscle primordium
- Endothelial cells are derived from lateral mesoderm and invasive angioblasts
- Endothelial progenitors from the second heart field create the endothelium of arches 3-6
- Pharyngeal endoderm is essential in regulating arch development
Typical Pharyngeal Arch
- A typical arch contains an artery, cartilage, and muscle components and is innervated by nerves from the primordial brain
- The artery branches from the truncus arteriosus of the primordial heart, passing around the primordial pharynx to enter the dorsal aorta
- Cartilage forms the skeleton of the arch
- Muscle differentiates into muscles for the head and neck
- Sensory and motor nerves originate from neuroectoderm of the primordial brain and supply to mucosa and muscles within the arch
Fate of Pharyngeal Arches
- Arches contribute to the face, nasal cavities, mouth, larynx, pharynx, and neck
- The second arch enlarges during the fifth week, overgrowing the third and fourth arches, forming the cervical sinus
- By the seventh week the second, third, and fourth grooves and cervical sinus have all disappeared leaving a smooth contour
Derivatives of Pharyngeal Arch Cartilages
- The dorsal end of the first arch cartilage (Meckel's cartilage) is associated with the developing ear
- Early nodules break away from the cartilage to form the malleus and incus (middle ear bones)
- The midpart of Meckel's cartilage regresses, perichondrium forms anterior ligament malleus and sphenomandibular ligament
- Ventral part of first arch cartilage forms horseshoe-shaped primordium of the mandible
- First arch cartilage guides mandible development, disappearing during intramembranous ossification
Derivatives of Pharyngeal Arch Cartilages (continued)
- The second arch cartilage (Reichert's cartilage) contributes to the development of the stapes (middle ear bone) and styloid process of the temporal bone
- Cartilage between the styloid and hyoid processes regresses, perichondrium of regresses cartilage forms stylohyoid ligaments
- The ventral end of the second arch cartilage ossifies to form the hyoid lesser cornu (lesser horn)
- The third arch cartilage ossifies to form the greater cornu of the hyoid and superior cornu of thyroid cartilages
- The body of the hyoid bone forms from the hypobranchial eminence
- Components of fourth/sixth arches form laryngeal cartilages, except epiglottis
- Cartilage of epiglottis originates from mesenchyme in the hypopharyngeal eminence
Derivatives of Pharyngeal Arch Muscles
- The muscular components derive from unsegmented paraxial mesoderm and prechordal plate
- First arch muscles are involved in mastication
- Second arch muscles form stapedius, styloid, and posterior belly of digastric
- Third arch muscles form stylopharyngeus
- Fourth arch muscles include cricothyroid, levator veli palatini, and constrictors of pharynx
- Sixth arch muscles form intrinsic muscles of the larynx
Derivatives of Pharyngeal Arch Nerves
- Each arch is supplied by its own cranial nerve
- Special visceral efferent (branchial) components of these nerves supply muscles
- Mesenchyme from the arches contributes to the dermis and mucous membranes of the head and neck
- These areas receive sensory innervation from special visceral afferent nerves (specific nerves supplying mucous membranes, face, teeth, tongue, palate)
- Trigeminal nerve (CN V) is principal sensory and motor nerve of muscles in mastication
- Facial nerve (CN VII), glossopharyngeal (CN IX), and vagal nerve (CN X) supply second, third, and fourth to sixth arches respectively
Pharyngeal Pouches
- The pharyngeal pouches are evaginations of the endoderm of the pharynx
- These pouches develop in a craniocaudal sequence between the arches
- The first pouch forms the auditory tube and tympanic cavity
- The second pouch forms part of the palatine tonsil
- Third pouch develops the inferior parathyroid gland
- The fourth pouch forms the superior parathyroid gland and ultimobranchial body
- Parts of the 4th & 6th pouches form parts of the thyroid gland
- Fifth pouch is rudimentary
Derivatives of the Pharyngeal Pouches
- The endodermal epithelial lining of the pouches creates important organs in the head and neck
- The first pouch expands into a tubotympanic recess that touches the first groove, eventually forming the tympanic membrane
- The second pouch cavity is largely obliterated, becoming the tonsillar sinus
- The third pouch yields the inferior parathyroid gland
- The fourth pouch gives rise to the superior parathyroid gland and ultimobranchial body
Cervical (Branchial) Sinuses
- External cervical sinuses are uncommon
- They result from failure of the second groove and cervical sinus to obliterate
- They open near the anterior border of the sternocleidomastoid muscle in the lower third of the neck
- Internal cervical sinuses open to the tonsillar sinus or near the palatopharyngeal arches
- Persistence of second pouch proximal portion can cause these sinuses
Cervical (Branchial) Fistula
- A fistula is an abnormal canal opening internally into the tonsillar sinus and externally on the side of the neck due to persistence in part of the 2nd pouch
- The canal ascends the neck through the subcutaneous tissue and platysma muscle, passing between the internal and external carotid arteries, to open into the tonsillar sinus
Piriform Sinus Fistula
- A piriform sinus fistula results from persistence of remnants of the ultimopharyngeal body extending to the thyroid gland
Cervical (Branchial) Cysts
- Remnants of cervical sinus or 2nd groove may persist, forming a spherical or elongated cyst in the neck inferior to the angle of the mandible
- They often appear as painless, slowly enlarging swellings in childhood or early adulthood
- Cysts enlarge due to the accumulation of fluid and cellular debris
First Pharyngeal Arch Syndrome
- Abnormal components of the first arch result in birth defects of the eyes, ears, mandible, and palate
- The most common types of this anomaly are Treacher Collins syndrome and Pierre Robin sequence
DiGeorge Syndrome
- Infants with DiGeorge syndrome are born without a thymus and parathyroid glands, having defects in cardiac outflow tracts
- In some cases, ectopic glandular tissue is present
- This syndrome is characterized by congenital susceptibility to hyperparathyroidism, increased infections, and birth defects
Ectopic Parathyroid Glands
- Ectopic parathyroid glands may lie near or within the thyroid or thymus
- The superior glands tend to be more constant in position than the inferior ones
- Multiple parathyroid glands are less common, likely occurring from division of original primordia
Development of Face
- Facial primordia emerge early in the fourth week around the stomodeum
- Facial development depends on inductive influences of the forebrain, frontonasal ectoderm, and developing eye
- Five facial primordia appear as prominences around the stomodeum
- Frontonasal prominence
- Paired maxillary prominences
- Paired mandibular prominences
Development of Face (continued)
- Maxillary and mandibular prominences are derivatives of the first pair of pharyngeal arches
- They are formed primarily from the expansion of neural crest cells originating from mesencephalic and rostral rhombencephalic neural folds
- These cells form the main connective tissue, cartilage, bone, and ligaments for the face and oral regions
Development of Face (continued)
- The frontonasal prominence surrounds the ventrolateral portion of the forebrain's optic vesicles, forming the eyes
- The frontal part of the frontonasal prominence creates the forehead, nasal portion creates the rostral boundary of the stomadeum and nose
- The maxillary prominences form the lateral boundary of the stomodeum and mandibular prominences form the caudal boundary of the stomodeum
- The facial prominences exhibit active growth centers in the underlying mesenchyme. This tissue is continuous
Facial Development (continued)
- Facial development is primarily between the fourth and eighth weeks of development
- By the end of the embryonic period, the face displays characteristic human features.
- Lower jaw and lower lip form through medial fusion of mandibular prominences. The incomplete fusion of these prominences creates a chin dimple
- The nose becomes more distinct and the mandible shows more growth during the fetal period
Nasal Development
- By the end of the fourth week, bilateral oval thickenings (nasal placodes) form on the infralateral aspects of the frontonasal prominence
- These nasal placodes expand, forming horseshoe-shaped medial and lateral nasal prominences
- Nasal placodes create nasal pits, which become the nostrils
- Lateral nasal prominences develop the alae (sides of the nose)
Auricle Development
- By the end of the fifth week, primordia of the auricles begin development
- Six auricular hillocks form around the first pharyngeal groove
- External acoustic meatus develops near these structures
- The auricles migrate to the sides of the head at the level of the eyes
Nasolacrimal Duct Development
- The nasolacrimal duct forms from an ectodermal thickening in the nasolacrimal groove.
- This thickening develops into a solid cord that separates from ectoderm and sinks into mesenchyme, canalizing to form a duct
- The superior end of the duct expands into the lacrimal sac.
Development of Nasal Prominences
- Medial nasal prominences fuse with maxillary prominences between weeks 7-10
- This merging generates continuity of the upper jaw and lip while separating the nasal pits from the stomodeum
Development of Intermaxillary Segment
- The medial nasal prominences merge to form the intermaxillary segment
- This segment forms the middle part (philtrum) of the upper lip, the premaxillary part of the maxilla, its associated gingivae, and primary palate
- Maxillary prominences extend medially to cover and shape the lower parts of the medial nasal prominences, creating the philtrum
Formation of Palate and Lips
- Early in the sixth week, the primordial jaws comprise mesenchymal masses
- Lip and gingival development arise from a thickening of ectoderm called a labiogingival lamina, which penetrates underlying mesenchyme
- Most labiogingival lamina degenerates, leaving the labiogingival groove
- A small area remains to form the frenum of the upper lip
- Face development continues slowly throughout the fetal period with changes in relative proportion and positions of facial components
- During the early fetal period, the nose is relatively flat, and the mandible is underdeveloped
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Test your knowledge on the development of pharyngeal arches with this comprehensive quiz. Explore the origins of components such as endothelial cells and mesenchyme, as well as the anatomical structures formed from these arches. Perfect for students of embryology and anatomy looking to deepen their understanding of this vital developmental process.
