Development of Pharyngeal Arches Dennis Flashcards
When do the pharyngeal arches develop?
They develop in early 4th week as the NC cells migrate to the future head and neck
What makes up the core of pharyngeal arches and what covers them externally/internally?
LO #1
Mesoderm and mesenchyme make up the core of each arch, ectoderm covers the arch externally, and endoderm covers the internal surface.
LO #3
Where does the mesenchyme that makes up the core of the arch come from?
embryonic CT derived from migratory NCC
LO #3
Where does the mesoderm of the head come from and what does it do for the arch?
Arises from paraxial mesoderm and gives each arch the ability to form PA muscles
LO #3
How does the lateral plate mesoderm contribute to the pharyngeal arch?
angioblasts differentiate into endothelium
LO #3
How does the prechordal plate mesoderm contribute to the pharyngeal arches?
extraocular muscles
What plays an essential role in regulating development of arches??
pharyngeal endoderm
What are the elements of pharyngeal arches?
- cartiliaginous rods form skeleton
- Muscular component
- Cranial nerves
- Arch artery
LO #4,6
What cartilage makes up pharyngeal arch 1 and what does the dorsal part form?
Meckel’s Cartilage which will form the malleus and incus
LO #4,6
What cartilage makes up the second pharyngeal arch and what does the dorsal region and ventral region form?
Riechert’s cartilage and the dorsal part will make the stapes and styloid process and the ventral portion will make the lesser horn of the hyoid
LO #4,6
What happens to the third pharyngeal arch cartilage?
It ossifies forming the greater horn of the hyoid
LO #4,6
What happens to the 4th and 6th arch cartilages?
4th forms laryngeal cartilages including epiglottis which is NCC derived
6th forms laryngeal cartialges also but origin is unknown
What muscles and nerves are associated with the first arch?
Muscles of mastication and trigeminal
What muscles and nerves are associated with the second arch?
Facial expression and stapedius Facial nerve
What muscles and nerves are associated with the third arch?
stylopharyngeus CN 9 glossopharyngeal
What muscles and nerves are associated with the fourth arch?
cricothyroid, pharyngeal constrictors and vagus nerve
What muscles and nerves are associated with the sixth arch?
intrinsic muscles of larynx and vagus nerve
What do the occipital myotomes give rise to?
tongue musculature
What does the prechordal plate give rise to?
extraocular muscles
What is Treacher Collins Syndrome?
First arch syndrome it is an autosomal dominant disorder with a mutation in the TCOF1 gene. Malar hypoplasia deformed ears and defectss of lower eyelids. Insufficient migration of NCC into 1 arch during the 4th week of development
What is Pierre Robin sequence?
First arch syndrome. Occurs de novo in patients and is associated with hypoplasia of mandible cleft palate and defects of ears and eyes. Micrognathia is initiating defect which will result in displacement of the tongue obstructing closure of the palate resulting in bilateral clefft palate
Where are pharyngeal grooves located and what are they covered with?
Externally between pharyngeal arches and covered with ectoderm
Where are pharyngeal pouches lcoated and covered with?
Internally as part of pharynx and they are covered with endoderm
What does the first groove form?
External acoustic meatus
What does the first pouch form?
Tubotympanic recess and tympanic cavity and mastoid antrum. The pouch elongates to form pharyngotympanic tube. Contributes to the tympanic membrane
what does the second pouch form?
Tonsillar sinus
Endoderm forms tonsillar epithelium
Mesenchyme forms lymphoid nodule of palatine tonsils
What does the third pouch form?
inferior parathyroid gland from the dorsal portion
thymus from the ventral portion
What does the fourth pouch form?
Dorsal part superior parathyroid glands
Ultimobranchial body fuses with thyroid gland and gives parafollicular cells
What is the external cervical sinus?
It is an anomaly when the 2nd groove and cervical sinus do not obliterate. Detected due to discharge of mucus and commonly associated with auricular sinuses
What is the Internal cervical sinus?
An anomaly, persistence of pouch two, it is rare and opens into tonsillar sinus or near palatopharyngeal arch
What is a cervical cyst?
Remnant of cervical sinus and/or 2nd groove. Slowly enlarging painless, free lying cyst in the neck inferior to the angle of the mandible. Accumulates fluid and cellular debris
What is a cervical fistula?
canal that opens into tonsillar sinus and external side of neck. It is a persistence of parts of the second groove and pouch. Ascends through the subcutaneous tissue and platysma to reach carotid sheath and passes btw carotids and opens into tonsillar sinus
When does the thyroid take on definitive shape?
7 weeks and the thyroglossal duct will degenerate
