Neck development Flashcards
sangeetha
how many pairs of pharyngeal pouches and clefts are present in 5 week embryo
4 pairs of clefts and 5 pouches but the last is often considered as part of 4th
what are the three tissue layers surrounding the pharyngeal arches
- outer ( ectoderm)
-inner( endoderm) - between them is mesenchyme and ectomesenchyme
what does the 1st pharyngeal cleft give rise to
EAM
contributes to tympanic membrane(eardrum): the 1st cleft forms the outer layer( ectodermal)
what happens to 2nd 3rd 4th clefts
2nd pharyngeal arch proliferates and overlaps them and form a space lined by epithelium and eventually lose contact with outside forming a cervical sinus
what happens to cervical sinus during development and what can its remnants cause
it will disappear but the remnants can lead to formation of lateral cervical cyst in childhood
what can result from failure of cervical sinus to disappear
pathological conditions such as cysts and fistulas
what do the pharyngeal arches give rise to
imp organs and and structures during development
what does the 1st pharyngeal pouch give rise to
proximal part forms Eustachian tube( auditory tube)
distal portion forms middle ear cavity
contributes to the tympanic membrane : forms inner layer ( endodermal) of eardrum
what does the 2nd pharyngeal pouch give rise to
it forms palatine tonsil and by the 3rd to 5th months the tonsil is infiltrated by lymphatic tissue
what does the 3rd pharyngeal pouch give rise to
dorsal wing forms : inferior parathyroid
ventral wing forms: thymus
what happens when the thymus migrates to thorax
the thymus will pull the inferior parathyroid gland with it and parathyroid rests on dorsal surface of thyroid gland
what does the 4th pharyngeal pouch give rise to
the epithelium forms the superior parathyroid gland and this gland attaches to the migrating thyroid and is located on dorsal surface of thyroid gland
what does the 5th pharyngeal pouch give rise to
ultimobranchial body which is incorporated into thyroid gland and gives rise to C-cells that will secrete CALCITONIN
when does the thyroid gland begin to develop
thyroid gland is the 1st endocrine gland to develop around the 4th week of intrauterine life
what is the origin of the thyroid gland
so it involves endodermal cells proliferating in the floor of primitive pharynx area at the foramen cecum
how is the thyroid gland development related to the 2nd pouch as the ppt mentioned
because the thyroid gland develops near the 2nd pouch but does not originate from it
role of foramen cecum in the early embryonic development
marks the origin point of the thyroid gland
how does the thyroid gland initially form
the gland forms as a bilobed diverticulum that descends in front of the pharyngeal gut
where does the thyroid gland migrate during development
migrates in front of hyoid bone and the laryngeal cartilages
what is the thyroglossal duct and what its significance
connects thyroid gland to the tongue during migration but later degenerates as the gland reaches its final position
what is the final position of thyroid gland by week 7 of embryonic development
positioned anterior to the trachea and it got median isthmus separating two lateral lobes
what is a thyroglossal cyst
its a remnant of thyroglossal duct
where can thyroglossal cyst be found
at any point along the pathway from foramen cecum to neck where thyroid gland descends
what are the symptoms of thyroglossal cyst
a midline neck mass that is movable and can become infected
