development of thyroid gland, tongue, and ear Flashcards
what is the first endocrine gland to develop in the embryo?
thyroid gland
when does thyroid gland development begin?
24 days after fertilization
the thyroid gland develops from a median endodermal thickening in the ___________
floor of a primordial pharynx
thyroid primordium
small outpouching that develops from the thickening in the floor of the primordial pharynx
the thyroid primordium comes from which pharyngeal pouch?
2nd
thyroglossal duct
narrow tube connecting the thyroid gland to the tongue that eventually dissolves
how are the two lobes of the thyroid gland connected?
isthmus of the thyroid gland
-lies anterior to the developing second and third tracheal rings
by what week does the thyroid assume definitive shape and reach its final site in the neck?
seventh week
the thyroglossal duct has normally degenerated by what week?
seventh week
foramen cecum
the proximal opening of the thyroglossal duct that persists
-small pit in tongue
the pyramidal lobe extends upward from the isthmus in about _____% of people
50%
levator of thyroid gland
fibrous tissue or smooth muscle that attaches the pyramidal lobe to the hyoid bone
the pyramidal lobe and associated smooth muscle represent a persistent part of the distal end of the _____
thyroglossal duct
site of origin of thyroglossal duct between floor of branchial arches 1 and 2
foramen cecum
what does the thyroid primordium consist of?
solid mass of endodermal cells
what does the cellular aggregation of the thyroid primordium break up into?
a network of epithelial cords
by what week do the cords divide into small cellular groups?
10
what forms in each cell cluster of the thyroid when the cells become arranged in a single layer?
lumen
what happens during the 11th week in thyroid development?
colloid begins to appear in each cell called thyroid follicles and iodine concentration and synthesis of thyroid hormones can be demonstrated
thyroid secretion reaches adult level by how many weeks?
35 weeks
congenital hypothyroidism (cretinism)
most common metabolic disorder in neonates
-common cause of intellectual disability
causes of congenital hypothyroidism
agenesis–failure of normal development of thyroid gland
ectopic thyroid–situated in a different location (e.g. beneath tongue)
signs and symptoms of congenital hypothyroidism
- retarded physical and mental growth
- spine curved and height is less than 3 ft
- head is large with wiry hair
- thick eyelids and large tongue
- abdomen protruding and sexual maturity not seen
treatment of congenital hypothyroidism
levothyroxine given to children
ectopic thyroid
thyroid develops in abnormal position
-mostly along course of thyroglossal duct
1/4000 people
most common site for ectopic thyroid
lingual
accessory thyroid gland tissue is–
lateral to thyroid cartilage
anomalies related to thyroglossal duct
cyst
sinus
fistula
t/f the thyroglossal duct disappears
true
what causes a thyroglossal cyst?
remnant of duct persists and forms a cyst in the tongue or anterior neck
thyroglossal cyst
painless, progressively enlarging, moveable mass
- observed at 5 yrs
- inferior to hyoid bone
- may contain thyroid tissue
thyroglossal duct sinus
following infection of a cyst
perforation of the skin
opens in the median plane of the neck, anterior to the laryngeal cartilages
thyroglossal duct may remain patent and open into external surface causing a —
fistula
arch development of tongue
arch 1– oral part of tongue (anterior 2/3)
arch 2–initial contribution to surface is lost
arch 3–pharyngeal part of tongue (posterior 1/3)
arch 4–epiglottis and adjacent regions
development of anterior 2/3 of tongue
- 3 swellings from 1st arch
- proliferation of mesenchyme in ventromedial parts of the 1st pair of pharyn arches
- median tongue bud (elevation) appears in floor of primordium pharynx near end of 4th week, just in front of foramen cecum–> swelling is first indication of tongue
- 2 oval distal tongue buds develop on each side of the median tongue bud
what grows over the median tongue bud?
lateral tongue buds increase in size and merge together overgrowing the median tongue bud
what forms the anterior 2/3 of the tongue?
merged distal tongue buds
how is the fusion of the distal tongue bud indicated?
a middle groove, the median sulcus of the tongue and internally by fibrous lingual septum
(median tongue bud forms no recognizable part of the adult tongue)
2 elevations that develop caudal to the foramen cecum to form the posterior 1/3 of tongue?
- copula: forms by fusion of ventromedial part of the 2nd pair of pharyngeal arches
- hypopharyngeal eminence: develops caudal to the copula from mesenchyme in ventromedial parts of the 3rd and 4th pairs of pharyngeal arches
what happens to the copula as the tongue develops?
gradually overgrown by the hypopharyngeal eminience and disappears
the pharyngeal part of the tongue develops from what?
the remaining part of the hypopharyngeal eminence
terminal sulcus
line of fusion of anterior and posterior parts of tongue
-v shaped
pharyngeal mesenchyme
connective tissue and vasculature of tongue
occipital myotomes
most of tongue muscles from myoblasts that migrate from occipial mytomes
innervates tongue muscles as they develop
hypoglossal nerve (XII)
the entire tongue is within the mouth at birth, its posterior third descends into the oropharynx by —– yrs old
4
tongue muscles are from ______ occipital myotomes
3,4,5
lingual papillae appear toward the end of the —- week
8
what kind of nerve endings do lingual papilla contain
afferent nerve endings
what papilla appear first
vallate and foliate
close to the terminal branches of glossopharyngeal nerve IX
filiform papillae
most common
threadlike shape
develp during early fetal period (10-11 wks)
when do fungiform papillae form?
later near termination of chorda tympani branch
when do taste buds develop
11-13 wks by active interaction bw epithelial cells of tongue and invading gustatory cells from chorda tympani and glossopharyngeal and vagus nerves
when is there a fetal response to bitter taste?
26-28 weeks
anterior 2/3 of tongue nerve supply
lingual branch of mandibular division of trigeminal
taste for anterior 2/3
chorda tympani except vallate papillae which are innervated by glossopharyngeal nerve (IX)
motor for anterior 2/3
hypoglossal
common sensation of tongue
trigeminal
nerve of 1st pharyngeal arch and this arch forms the median and distal tongue buds
trigeminal
nerve of second phar arch
facial
palatoglossus is supplied by?
vagus
the posterior 3rd of tongue is innervated by ?
glossopharyngeal from 3rd arch
superior laryngeal branch of vagus supplies?
small area of tongue anterior to epiglottis
the vagus nerve is of the — arch
4
all muscles of the tongue are supplied by _____ except for _____
all by hypoglossal except palatoglossus which is supplied from pharyngeal plexus by fibers from vagus nerve
aglossia
no tongue
feeding, breathing, and speech issue
bifid tongue
failure of fusion of 2 lateral lingual swelling
congenital lingual cyst of fistula
persistent lingual part of thyroglossal duct
tongue tie (ankyloglossia)
short, thick band of tissue which connects the lip of tongue to floor of mouth and restricts movement of tongue
microglossia
small tongue
-with microgenitalia and limb defects
macroglossia
large tongue
- trisomy 21
- acromegaly
- mucopolysaccharidoses
- congential hypothyroidism
- diabetes
3 anatomical parts of ear
- external –auricle, external auditory meatus, outer layer of tympanic membrane
- middle–3 auditory ossicles (stapes, incus, malleus), inner layer of tympanic membrane
- internal–vestibulocochlear organ (cochlea and semicircular canal)
external auditory canal develops from–
surface ectoderm that covers the dorsal end of the 1st pharyngeal groove
meatal plug
solid epithelial plate that develops at bottom of funnel shaped pharyngeal groove
what lines the middle ear?
1st pharn pouch endoderm
eustachan tube
connects pharynx to ear
malleus and incus form from the mesoderm of the — arch
1st arch
mechel’s cartilage
stapes forms from
mesoderm of 2nd arch
reichert’s cartilage
ossicles are full sized by ____
15 weeks
ossicles ossify by
25 weeks
tensor tympani supplied by —
mandibular nerve (1st arch)
stapedius supplied by
facial nerve (2nd arch)
the first brachial arch is also called
mandibular arch
second arch is called
hyoid arch
in between 1st and 2nd brachial arch is called the
ectodermal cleft
ectoderm of internal ear
membranous labyrinth
bony labyrinth
mesoderm of internal ear
what happens in the 3rd week of internal ear development?
surface ectoderm–otic placode invaginates into otic pit
4th week in ear development
pit edges fuse to become otic vesicle (primordium of membranous labyrinth)
otic vesicle separates from surface ectoderm, elongates, and forms the _____
endolymphatic duct and sac
dorsal utericular part of ear
forms endolymphatic and semicircular ducts and utericle
ventral saccular part of ear
forms saccules and cochlear duct
congenital deafness
inner ear deafness (rubella)
middle ear deafness, anomalies of 1st and 2nd arches
auricular anomalies of ear
accessory auricle, absence of auricle, small auricle
atresia of external auditory meatus
failure of canalization
congenital cholestotoma
keratin filled cysts that grow medial to tympanic membrane result either from birth abnormality, trauma or metaplasia
what criteria do conditions need to fulfill in order for them to be a congenital ear disorder?
- mass medial to tympanic membrane
- normal tympanic membrane
- no previous history of ear discharge, perforation, or surgery
