THYROID GLAND & TONGUE

THYROID GLAND & TONGUETHYROID GLAND & TONGUE

Dr. Mujahid KhanDr. Mujahid Khan

Development of ThyroidDevelopment of Thyroid

The thyroid gland is the first endocrine gland to The thyroid gland is the first endocrine gland to develop in embryodevelop in embryo

It begins to form about 24 days after fertilizationIt begins to form about 24 days after fertilization

It develops from a median endodermal It develops from a median endodermal thickening in the floor of a primordial pharynxthickening in the floor of a primordial pharynx

Thickening soon forms a small outpouching Thickening soon forms a small outpouching called thyroid primordiumcalled thyroid primordium


As the embryo and tongue grow, the As the embryo and tongue grow, the developing thyroid gland descends in the developing thyroid gland descends in the neck, passing ventral to the developing neck, passing ventral to the developing hyoid bone and laryngeal cartilageshyoid bone and laryngeal cartilages

For a short time the thyroid gland is For a short time the thyroid gland is connected to the tongue by a narrow tube, connected to the tongue by a narrow tube, the thyroglossal ductthe thyroglossal duct


At first the thyroid primordium is hollow but it At first the thyroid primordium is hollow but it soon becomes solid and divides into right and soon becomes solid and divides into right and left lobesleft lobes

The two lobes are connected by the isthmus of The two lobes are connected by the isthmus of the thyroid glandthe thyroid gland

Isthmus lies anterior to the developing second Isthmus lies anterior to the developing second and third tracheal ringsand third tracheal rings

By seventh week it assumes the definitive shape By seventh week it assumes the definitive shape and has reached its final site in the neck and has reached its final site in the neck


The thyroglossal duct has normally The thyroglossal duct has normally degenerated by seventh weekdegenerated by seventh week

The proximal opening of the thyroglossal The proximal opening of the thyroglossal duct persists as a small pit in the tongue, duct persists as a small pit in the tongue, the foramen cecumthe foramen cecum

A pyramidal lobe extends upward from the A pyramidal lobe extends upward from the isthmus in about 50% of peopleisthmus in about 50% of people


The pyramidal lobe may be attached to the The pyramidal lobe may be attached to the hyoid bone by fibrous tissue or smooth hyoid bone by fibrous tissue or smooth muscle, the levator of thyroid glandmuscle, the levator of thyroid gland

The pyramidal lobe and the associated The pyramidal lobe and the associated smooth muscle represent a persistent part smooth muscle represent a persistent part of the distal end of the thyroglossal ductof the distal end of the thyroglossal duct

Histogenesis of ThyroidHistogenesis of Thyroid

The thyroid primordium consists of a solid mass of endodermal cellsThe thyroid primordium consists of a solid mass of endodermal cells

The cellular aggregation later breaks up into a network of epithelial The cellular aggregation later breaks up into a network of epithelial cords cords

By the tenth week the cords have divided into small cellular groupsBy the tenth week the cords have divided into small cellular groups

A lumen soon forms in each cell cluster and the cells become arranged A lumen soon forms in each cell cluster and the cells become arranged in a single layer around the lumenin a single layer around the lumen

During the eleventh week colloid begins to appear in these structures, During the eleventh week colloid begins to appear in these structures, called thyroid folliclescalled thyroid follicles

Iodine concentration and synthesis of thyroid hormones can be Iodine concentration and synthesis of thyroid hormones can be demonstrateddemonstrated

Thyroglossal Duct Cysts & Thyroglossal Duct Cysts & SinusesSinuses

Cyst may form anywhere along the course Cyst may form anywhere along the course followed by the thyroglossal duct during descent followed by the thyroglossal duct during descent of the primordial thyroid gland from the tongueof the primordial thyroid gland from the tongue

Normally the thyroglossal duct atrophies and Normally the thyroglossal duct atrophies and disappear disappear

A remnant of it may persist and form a cyst in A remnant of it may persist and form a cyst in the tongue or in the anterior part of the neckthe tongue or in the anterior part of the neck


It usually lies just inferior to the hyoid boneIt usually lies just inferior to the hyoid bone

Most thyroglossal duct cysts are observed by the Most thyroglossal duct cysts are observed by the age of 5 yearsage of 5 years

The swelling produced is usually develops as a The swelling produced is usually develops as a painless, progressively enlarging, moveable masspainless, progressively enlarging, moveable mass

The cyst may contain some thyroid tissueThe cyst may contain some thyroid tissue


Following infection of a cyst, a perforation Following infection of a cyst, a perforation of the skin occurs forming a thyroglossal of the skin occurs forming a thyroglossal duct sinusduct sinus

It usually opens in the median plane of the It usually opens in the median plane of the neck, anterior to the laryngeal cartilagesneck, anterior to the laryngeal cartilages

Development of TongueDevelopment of Tongue

A median triangular elevation appears in the A median triangular elevation appears in the floor of the primordium pharynx near the end of floor of the primordium pharynx near the end of 44thth week, just rostral to the foramen cecum week, just rostral to the foramen cecum

This swelling or median tongue bud is the first This swelling or median tongue bud is the first indication of tongue developmentindication of tongue development

Soon two oval distal tongue buds develop on Soon two oval distal tongue buds develop on each side of the median tongue budeach side of the median tongue bud


The three lingual buds result from the The three lingual buds result from the proliferation of mesenchyme in ventromedial proliferation of mesenchyme in ventromedial parts of the first pair of pharyngeal archesparts of the first pair of pharyngeal arches

The distal tongue buds rapidly increase in size, The distal tongue buds rapidly increase in size, merge with each other, and overgrow the merge with each other, and overgrow the median tongue budmedian tongue bud

The merged distal tongue buds form the anterior The merged distal tongue buds form the anterior two-thirds (oral part) of the tonguetwo-thirds (oral part) of the tongue


Fusion of the distal tongue buds is Fusion of the distal tongue buds is indicated by a middle groove, the median indicated by a middle groove, the median sulcus of the tongue and internally by the sulcus of the tongue and internally by the fibrous lingual septumfibrous lingual septum

Median tongue bud forms no recognizable Median tongue bud forms no recognizable part of the adult tonguepart of the adult tongue

Formation of Posterior third of Formation of Posterior third of TongueTongue

It is indicated by two elevations that develop It is indicated by two elevations that develop caudal to the foramen cecumcaudal to the foramen cecum

Copula: Forms by fusion of the ventromedial part Copula: Forms by fusion of the ventromedial part of the second pair of pharyngeal archesof the second pair of pharyngeal arches

The hypopharyngeal eminence: Develops The hypopharyngeal eminence: Develops caudal to the copula from mesenchyme in the caudal to the copula from mesenchyme in the ventromedial parts of the third and fourth pairs of ventromedial parts of the third and fourth pairs of archesarches


As the tongue develops the copula is gradually As the tongue develops the copula is gradually overgrown by the hypopharyngeal eminence overgrown by the hypopharyngeal eminence and disappear and disappear

As a result, the pharyngeal part of the tongue As a result, the pharyngeal part of the tongue develops from the rostral part of the develops from the rostral part of the hypopharyngeal eminencehypopharyngeal eminence

The line of fusion of the anterior and posterior The line of fusion of the anterior and posterior parts of the tongue is roughly indicated by a V-parts of the tongue is roughly indicated by a V-shaped groove called terminal sulcusshaped groove called terminal sulcus


Pharyngeal mesenchyme forms the connective tissue Pharyngeal mesenchyme forms the connective tissue and vasculature of the tongueand vasculature of the tongue

Most of the tongue muscles are derived from myoblasts Most of the tongue muscles are derived from myoblasts that migrate from the occipital myotomesthat migrate from the occipital myotomes

The hypoglossal nerve (CN The hypoglossal nerve (CN ⅫⅫ) accompanies the ) accompanies the myoblast during their migration and innervates the myoblast during their migration and innervates the tongue muscles as they developtongue muscles as they develop

The entire tongue is within the mouth at birth, its The entire tongue is within the mouth at birth, its posterior third descends into the oropharynx by 4 years posterior third descends into the oropharynx by 4 years of age of age

Papillae and Taste BudsPapillae and Taste Buds

Lingual papillae appear towards the end of the Lingual papillae appear towards the end of the eighth weekeighth week

The vallate and foliate papillae appear first, The vallate and foliate papillae appear first, close to the terminal branches of the close to the terminal branches of the glossopharyngeal nerve (CN glossopharyngeal nerve (CN Ⅸ)Ⅸ)

The fungiform papillae appear later near The fungiform papillae appear later near termination of chorda tympani branch of termination of chorda tympani branch of the facial nervethe facial nerve

Papillae and Taste BudsPapillae and Taste Buds The most common lingual papillae, known as The most common lingual papillae, known as

filiform papillae because of their threadlike filiform papillae because of their threadlike shape, develop during early fetal period (10-11 shape, develop during early fetal period (10-11 weeks)weeks)

They contain afferent nerve endings sensitive to They contain afferent nerve endings sensitive to touchtouch

Taste buds develop during 11-13 weeksTaste buds develop during 11-13 weeks

Most taste buds form on the dorsal surface of Most taste buds form on the dorsal surface of the tonguethe tongue

Papillae and Taste BudsPapillae and Taste Buds

Fetal responses in the face can be Fetal responses in the face can be induced by bitter tasting substances at 26-induced by bitter tasting substances at 26-28 weeks, indicating that the reflex 28 weeks, indicating that the reflex pathways between taste buds and facial pathways between taste buds and facial muscles are established by this agemuscles are established by this age

Nerve Supply of the TongueNerve Supply of the Tongue

The development of tongue explains its nerve The development of tongue explains its nerve supplysupply

The sensory supply to the mucosa of almost the The sensory supply to the mucosa of almost the entire anterior two-thirds of the tongue is from entire anterior two-thirds of the tongue is from the lingual branch of the mandibular division of the lingual branch of the mandibular division of the trigeminal nervethe trigeminal nerve

This nerve is the nerve of first pharyngeal arch This nerve is the nerve of first pharyngeal arch and this arch forms the median and distal and this arch forms the median and distal tongue budstongue buds


Facial nerve is the nerve of second pharyngeal Facial nerve is the nerve of second pharyngeal arch arch

Its chorda tympani branch supplies the taste Its chorda tympani branch supplies the taste buds in the anterior two-thirds of the tongue buds in the anterior two-thirds of the tongue except the vallate papillaeexcept the vallate papillae

The facial nerve does not supply any of the The facial nerve does not supply any of the tongue mucosa, except for taste buds in the oral tongue mucosa, except for taste buds in the oral part of the tongue part of the tongue


The vallate papillae in the oral part of the tongue The vallate papillae in the oral part of the tongue are innervated by glossopharyngeal nerve (CN are innervated by glossopharyngeal nerve (CN ⅨⅨ) of the third pharyngeal arch) of the third pharyngeal arch

This is due to the reason that mucosa of This is due to the reason that mucosa of posterior two third of the tongue is pulled slightly posterior two third of the tongue is pulled slightly anteriorly as the tongue developsanteriorly as the tongue develops

The posterior third of the tongue is innervated The posterior third of the tongue is innervated mainly by the glossopharyngeal nerve, which is mainly by the glossopharyngeal nerve, which is a nerve of third pharyngeal archa nerve of third pharyngeal arch


The superior laryngeal branch of the vagus The superior laryngeal branch of the vagus nerve (CN nerve (CN ⅩⅩ) of the fourth arch supplies small ) of the fourth arch supplies small area of the tongue anterior to the epiglottisarea of the tongue anterior to the epiglottis

All muscles of the tongue are supplied by the All muscles of the tongue are supplied by the hypoglossal nerve (CN hypoglossal nerve (CN ⅫⅫ), except for ), except for palatoglossus, which is supplied from palatoglossus, which is supplied from pharyngeal plexus by fibers arising from the pharyngeal plexus by fibers arising from the vagus nervevagus nerve

THYROID GLAND & TONGUE

Documents

THYROID GLAND & TONGUE