Development of Pharyngeal Arches Flashcards
What are the 4 components of the pharyngeal apparatus?
Pharyngeal arches
Pharyngeal pouches
Pharyngeal grooves (clefts)
Pharyngeal membranes
The pharyngeal arches develop early in the ____ week as ______ cells migrate from the neural tube into the future head and neck
4th; neural crest
The 1st pair of arches, the primordial ______, appear as surface elevations lateral to the developing pharynx.
Arches ____- ___ soon appear as ridges on each side of the future head and neck regions.
The _____-____ arches are rudimentary and not visible on the surface of the embryo. The _____ arch may not form, or may quickly degenerate.
Jaws
2;4
5;6;5th
Neural crest cells migrate to form the pharyngeal arches from what 3 initial brain divisions? The majority of neural crest contribution comes from which division?
Forebrain
Midbrain
Hindbrain (major contributor)
The hindbrain is divided into 7 segments called _______ which are what contribute the NCCs to the pharyngeal arches
Rhombomeres
Pharyngeal arch 1 receives streams of neural crest cells from which rhombomere(s)?
R1-2
Pharyngeal arch 2 receives streams of neural crest cells from which rhombomere(s)?
R4
Pharyngeal arches 3-4 receive streams of neural crest cells from which rhombomere(s)?
R6-7
Which rhombomeres produce very few NCCs?
R3 and R5
Each pharyngeal arch consists of a core of ________, covered externally by _____ and internally by _______
Mesenchyme; ectoderm; endoderm
The mesenchyme core of the pharyngeal arches is derived from what type of cells?
The neural crest cells that migrate into the arches during the 4th week
The pharyngeal arches support the lateral walls of the primordial ________. Neural crest cell migration into the first arch and differentiation into mesenchyme form the _____ and ______ prominences
Pharynx; maxillary; mandibular
In the 5th week of development, after the first arch as separated into the maxillary and mandibular prominences, pharyngeal arch 2 overgrows 3 and 4, forming the ____ ______, an ______ depression that should disappear by the end of the 7th week (otherwise resulting in birth defects)
Cervical sinus; ectodermal
In addition to forming the maxillary and mandibular prominences, NCC will form what other general pharyngeal arch components?
All connective tissue, including the dermis (integument), and smooth muscle
________ _______ (paraxial) moves into each arch forming a central core of muscle primordium
Myogenic mesoderm
_________ (from lateral plate mesoderm) differentiate into endothelium components of pharyngeal arches
Angioblasts
Pharyngeal _______ plays an essential role in regulating the development of the arches
Endoderm
A typical pharyngeal arch contains several structures:
An artery arises from the ____ ____ of the primordial heart, which passes around the primordial pharynx to enter the ____ _____.
A ______ _____forms the skeleton of the arch.
A muscular component differentiates into muscles in the head/neck. Sensory and motor nerves supply mucosa and muscles derived from each arch. Nerves are derived from the developing ____ which then grow into the arches
Truncus arteriosus; dorsal aorta
Cartilaginous rod
Brain
Cartilage of pharyngeal arch 1
Meckel’s cartilage
Meckel’s cartilage = cartilage of PA1. Dorsal nodules of meckel’s cartilage break away to form the ____ and ______
Malleus; incus
Perichondrium of meckel’s cartilage (PA1) will form the ____ ____ of the malleus and _______ ligament
Anterior ligament; sphenomandibular
Ventral parts of meckel’s cartilage (PA1) will form the primordium of the ______, but this is just acting as a placeholder until the bone can form laterally and the cartilage disappears
Mandible
Cartilage of PA2
Riechert’s cartilage
Riechert’s cartilage (PA2) + an independent dorsal anlage will form the _____ as well as the _____ ____ of the temporal bone
Stapes; styloid process
The cartilage between the styloid and the hyoid eventually regresses, and the perichondrium of Riechert’s cartilage (PA2) will form the ______ ligament
Stylohyoid
The ventral end of Riechert’s cartilage (PA2) ossifies and forms what structure?
Lesser horn of hyoid bone
The third pharyngeal arch cartilage ossifies and becomes what structure?
Greater horn of hyoid bone
What forms the body of the hyoid bone?
The hypopharyngeal eminence, which is a prominence in the floor of embryonic pharynx (from pharyngeal arches 3 and 4)
What is the fate of the 4th and 6th pharyngeal arches?
They fuse, forming laryngeal cartilages (except epiglottis)
T/F: the fifth arch has no derivatives
True
Muscular components of pharyngeal arches are derived from what 2 sources?
Paraxial mesoderm
Prechordal plate
What muscles and corresponding n. are associated with the first arch?
Muscles of mastication (CN V)
What muscles and corresponding n. are associated with the second arch?
Stapedius and muscles of facial expression (CN VII)
What muscles and corresponding n. are associated with the third arch?
Stylopharyngeus (CN IX)
What muscles and corresponding n. are associated with the fourth arch?
Cricothyroid
Levator veli palatini
Pharyngeal constrictors
CN X
What muscles and corresponding n. are associated with the sixth arch?
Intrinsic mm of the larynx (CN X)
Each pharyngeal arch is supplied by its own cranial n. Special visceral efferents supply _____ derived from the arches. Special visceral afferents supply ______ and _______ of the head and neck.
Muscles; dermis; mucous membranes
How does the trigeminal n. contribute to the pharyngeal arches?
Supplies the first arch
Principle sensory n. of head and neck — innervates face, teeth, mucous membranes of nasal cavities, palate, mouth, and tongue
Motor nerve for muscles of mastication
How does the facial n. (CN VII) contribute to the pharyngeal arches?
Supplies 2nd arch
Muscles of facial expression
How does the glossopharyngeal n. (CN IX) contribute to the pharyngeal arches?
Supplies 3rd arch
Stylopharyngeus m.
How does the vagus n. (CN X) contribute to the pharyngeal arches?
Supplies 4th and 6th arches
4th arch is supplied by superior laryngeal branch of CN X and its recurrent laryngeal branch
Constrictos of pharynx (4th) and intrinsic mm of larynx (6th)
The primordial pharynx is derived from _______ and widens cranially as it joins the _______, but narrows as it joins the esophagus.
________ of the pharynx lines the internal aspects of the pharyngeal arches as associated pouches
Foregut; stomodeum
Endoderm
_____ pairs of pharyngeal pouches develop in a craniocaudal sequence between the arches
The first forms between the ___ and ____ arches
Five
1st; 2nd
Which pair of pharyngeal pouches is rudimentary, if present?
5th pair
Pharyngeal pouch endoderm contacts the ectoderm of pharyngeal grooves, which forms a double-layered ______ ________ which separates pouches from grooves
Pharyngeal membrane
Pharyngeal membranes appear in the floors of the pharyngeal grooves, forming where the epithelia of the grooves and pouches meet. This area is quickly infiltrated and separated by mesenchyme, obliterating all but the _____ pharyngeal membrane, which combines with intervening mesenchyme to form the ____ _____
1st; tympanic membrane
The epithelial lining of the pharyngeal pouches, which is ______ germ layer, forms important organs in the head/neck
Endoderm
The first pharyngeal pouch expands into an elongated _____ ______. An expanded distal part of this structure contacts the 1st groove, contributing to part of the _____ _____ (the other part coming from the 1st pharyngeal membrane)
Tubotympanic recess; tympanic membrane
The cavity of the tubotympanic recess formed by the first pharyngeal pouch forms the _____ ___ and _____ _____
The connection of the tubotympanic recess with the pharynx elongates, which forms the _______ _____
Tympanic cavity; mastoid antrum
Pharyngotympanic tube
The second pharyngeal pouch is largely obliterated as the ____ ___ develops, BUT part of the cavity of this pouch remains as the ____ ____ (fossa), which is a depression between the palatoglossal and palatopharyngeal arches
Palatine tonsil; tonsillar sinus
Endoderm of the second pharyngeal pouch proliferates - of which the central core will break down to form the ____ ______, the remainder will form surface epithelium of the tonsils and the lining of the above structure
Mesenchyme around the crypts differentiates into _____ tissue at 20 wks, later organizing into _____ _____ of the palatine tonsil
Tonsillar crypts
Lymphoid; lymphatic nodules
The third pharyngeal pouch will expand and form a solid, dorsal bulbar part and a hollow, elongated ventral part.
By the 6th week, the epithelium of the dorsal bulbar part differentiates into the ______ _____ _____. Epithelium of the elongated ventral parts proliferates, obliterating the cavities. Portions then come together in the median plane to form the _______
Glands lose connections with the pharynx due to growth of brain and cardiac regions, resulting in caudal displacement of derivatives of 2nd-4th pouches
Inferior parathyroid glands; thymus
[note that the inferior parathyroid glands will separate from thymus at later stage]
The fourth pharyngeal pouch expands and forms a dorsal, bulbar part as well as an elongated, ventral part.
By the 6th week, epithelium of dorsal bulbar part differentiates into a ____ ____ ____ which lies on the dorsal surface of the thyroid gland.
The fourth pouch also gives rise to the _____ body
Superior parathyroid gland
Ultimopharyngeal
Pharyngeal ______ separate the pharyngeal arches and are separated externally. They are numbered 1-4 from cranial to caudal and arise during the 4th-5th weeks.
The first pair persists as the _____ ____ _____
Pairs 2-4 lie in the ____ ____, a slit-like depression, and should be obliterated by the 7th week as the neck develops.
Grooves
External acoustic meatus
Cervical sinus
[note that birth defects of 2nd groove are common]
Remnants of cervical sinus and/or the 2nd pharyngeal groove which persist and form a spherical/elongated cyst d/t collections of epithelial debris and fluid
Cervical (branchial) cysts
Cervical (branchial) cysts often lie free in the neck, inferior to the angle of the ______; they also occur along the anterior border of the ____ m.
They are apparent until late childhood/early adulthood as slowly enlarging, painless swellings in the neck; also possible that they remain patent as fistulas or periauricular openings
Mandible; SCM
What is the first endocrine gland to develop, at 24 days post fertilization?
Thyroid primordium
Thyroid primordium forms from a median ______ thickening in the floor of the primordial pharynx. It descends into the neck with tongue growth and passes ____ to the developing hyoid bone and _______ cartilages
It is connected to the tongue by a narrow tube called the ______ duct
Endodermal; ventral; laryngeal
Thyroglossal
At 7 wks, the thyroid starts out as a small mass of endodermal cells which are broken up into epithelial ____ by vascular mesenchyme. At this point the thyroglossal duct has normally degenerated, except for the proximal opening which persists as the _____ ____ on the dorsal tongue. The _______ lobe is variably present and extends superiorly from the isthmus in 50% of people
Cords; foramen cecum; pyramidal
By the 10th week, the epithelial cords of the future thyroid have divided into cellular groups and a lumen. The cells are arranged into a single layer around thyroid _______
At the 11th week, colloid appears and synthesis of ____ occurs
At 20 weeks, levels fetal ____ and _____ increase
At 35 weeks, levels of the above 2 hormones reach adult levels
Follicles
TH
TSH; thyroxine
The elongated ventral part of the 4th pharyngeal pouch forms the _____ ____ which fuses with the thyroid gland
Cells disseminate within the thyroid and form ______ cells (derived from _______ cells), which produce calcitonin (lowering blood Ca)
Ultimopharyngeal body
Parafollicular; neural crest
Malformation of eyes, ears, mandible, and palate which together constitute ____ ____ syndrome
First arch
What general developmental event causes first arch syndrome?
Insufficient migration of NCCs into the 1st arch during the 4th week
Describe treacher collins syndrome
First arch syndrome that is also called mandibulofacial dysostosis
Characterized by malar hypoplasia with down-slanting palpebral fissures, defects of lower eyelids, deformed external ears and sometimes other ear structures
Autosomal dominant; mutations in TCOF1 which encodes TREACLE protein involved in ribosome biogenesis —> increased apoptosis of cranial NCCs
What first pharyngeal arch syndrome typically occurs de novo and is associated with hypoplasia of the mandible, cleft palate, and defects of the eyes and ears?
Pierre Robin sequence
What is the initiating defect in Pierre robin sequence?
Small mandible (micrognathia) —> results in posterior displacement of the tongue and obstruction of full closure of the palate resulting in bilateral cleft palate
Absence of a thyroid gland or one of its lobes
Thyroid agenesis
Unilateral failure of thyroid formation
Thyroid hemiagenesis
Which lobe of the thyroid is more commonly absent in thyroid hemiagenesis?
Left lobe
[mutations in the receptor for TSH are likely involved]
What syndrome is characterized by agenesis of thymus and parathyroid glands, congenital hypoparathyroidism, shortened philtrum of upper lip, low set ears, nasal clefts, thyroid hypoplasia, and cardiac abnormalities?
DiGeorge syndrome
The aortic arch artery system initially consists of 5 pairs of arteries that arise from the ____ ____. These are remodeled to form great arteries of the thorax and branches that supply the head/neck.
The common and internal carotids are the ____ arch arteries.
The distal internal carotids are extensions of the ____ ____
The external carotids form de novo from the ___ ____
Aortic sac
3rd
Dorsal aorta
Common carotids
Endothelium of the head vasculature and aortic arch arteries arises from what germ layer?
Mesoderm
Histogenesis of parathyroid glands: epithelium of the dorsal parts of the ___ and ____ pouches proliferates in 5th week. Small nodules form on dorsal aspect of each pouch. Vascular _____ invests and forms capillary network. ______ cells differentiate during the embryonic period, secreting PTH, which regulates fetal Ca metabolism. ____ cells differentiate at 5-7yrs of age
3rd; 4th; mesenchyme; Chief (principal); oxyphil
Histogenesis of the thymus: thymic primordium develops from epithelial cells derived from endoderm of 3rd pair of pouches. Epithelial tubes grow into mesenchyme and become solid cords that proliferate, forming side branches. Each side branch becomes the core of a lobule of the thymus. Some epithelial cords become arranged around a central point, forming ____ _____. Other epithelial cords spread apart, but keep their connections to form an epithelial ______, which will be invaded by lymphocytes. Growth and development of the thymus are not complete at birth, and will actively contibue during childhood until it eventually involutes
Thymic corpuscles (Hassall corpuscles); reticulum
