Tongue and Thyroid Development

Flashcards covering the embryological development of the human tongue and thyroid gland based on clinical embryology lecture notes.

Oral part of the tongue

The anterior $\frac{2}{3}$ of the tongue.

Pharyngeal part of the tongue

The posterior $\frac{1}{3}$ of the tongue.

Lateral lingual swellings

Two swellings from the first pharyngeal arch that form the anterior $\frac{2}{3}$ of the tongue.

Tuberculum impar

A small median triangular swelling in the floor of the primitive pharynx, also known as the median swelling of the first arch.

Hypobranchial eminence

A large median swelling (copula of His) associated with the second, third, and fourth pharyngeal arches.

Occipital myotomes

The source of the myoblasts that migrate into the tongue to develop its muscles.

End of 4th week of IUL

Timing for the appearance of the tuberculum impar in the floor of the primitive pharynx.

Foramen cecum

A blind depression in the floor of the primitive pharynx marking the site of thyroid gland development.

Distal tongue buds

Another name for the two lateral lingual swellings.

Median sulcus

The line of fusion of the two lateral lingual swellings on the dorsal surface of the tongue.

Nerve of the first arch

The mandibular branch of the trigeminal nerve.

Nerve of the third arch

The glossopharyngeal nerve.

Nerve of the fourth arch

The superior laryngeal nerve.

Sulcus terminalis

A V-shaped groove marking the line of fusion between the anterior $\frac{2}{3}$ and posterior $\frac{1}{3}$ of the tongue.

Epiglottis development

Develops from the caudal part of the hypobranchial eminence.

Hypoglossal nerve

The nerve of the occipital myotomes that accompanies myoblasts during migration to the tongue.

Tongue location at birth

At birth, both the anterior and posterior parts are located within the oral cavity.

Age of posterior tongue descent

$4\,\text{years}$ of age, when the posterior third descends into the oropharynx.

Median plane structure (Tongue)

The median sulcus formed by the fusion of lingual swellings.

Mucous membrane origin

Derived from the endoderm of the primitive foregut.

Fibroareolar tissue origin

Develops from the mesenchyme of the pharyngeal arches.

Linguogingival sulcus

A sulcus that develops to separate the tongue from the floor of the mouth.

Aglossia

Complete absence of the tongue due to agenesis of tongue primordia.

Hemiglossia

A condition occurring if one of the lateral lingual swellings fails to develop.

Ankyloglossia

Also known as tongue tie, caused by the frenulum extending to the tip of the tongue.

Bifid tongue

Failure of fusion of the two lateral lingual swellings resulting in a split anterior tongue.

Ankyloglossia superior

A rare condition where the tongue is adherent to the palate.

Lingual nerve

A branch of the mandibular nerve that provides general sensory innervation to the anterior $\frac{2}{3}$ of the tongue.

Chorda tympani nerve

A branch of the facial nerve providing special taste sensation to the anterior $\frac{2}{3}$ of the tongue.

Internal laryngeal nerve

Carries taste sensations from the posterior-most part of the tongue.

Beer drinker’s nerve

A clinical nickname for the internal laryngeal nerve.

Thyroglossal duct

An endodermal diverticulum in the floor of the primitive pharynx that forms the thyroid gland.

Parafollicular cells

Also called C cells, they develop from neural crest cells and produce calcitonin.

Ultimobranchial body

Formed by the fusion of the fourth and fifth pharyngeal pouches; also called the caudal pharyngeal complex.

Thyroid development start time

Begins during the third week of IUL as an endodermal thickening.

Thyroid functioning start time

The thyroid gland starts functioning by the end of the third month of IUL.

Thyroid isthmus location

Lies anterior to the developing second and third tracheal rings.

Pyramidal lobe

A structure present in $50\%$ of people, differentiating from the distal end of the thyroglossal duct.

Levator glandulae thyroideae

A band of fibrous tissue or smooth muscle attaching the pyramidal lobe to the hyoid bone.

Thyroid follicles

Thyroid cells arranged around a lumen produced by epithelial cords group division.

Colloid

A source of thyroxine and triiodothyronine produced in the thyroid follicle lumen by the 12th week of IUL.

Calcitonin

A hormone produced by C cells derived from the caudal pharyngeal complex.

Lingual thyroid

The most common abnormal site for thyroid tissue, located within or under the tongue mucosa.

Sublingual thyroid

Thyroid tissue located in the neck above, at, or just below the hyoid bone.

Intrathoracic thyroid

A condition where all or part of the thyroid gland is located in the thorax.

Occult carcinoma of thyroid

Thyroid carcinoma that is less than $1.5\,cm$ in diameter.

Lateral aberrant thyroid

Historically misnamed; usually refers to metastasis in cervical lymph nodes from occult carcinoma.

Thyroid hemiagenesis

Absence of one lateral lobe of the thyroid gland, commonly seen on the left side.

Thyroglossal cyst

A cyst formed when parts of the thyroglossal duct persist along its course.

Thyroglossal fistula

An external opening on the neck surface caused by a ruptured thyroglossal cyst.

Accessory thyroid

Small nodules of thyroid tissue in close proximity to the normal thyroid gland.

First endocrine gland to develop

The thyroid gland.

Vallate and foliate papillae

The first lingual papillae to develop.

Fetal facial responses to bitter taste

Can be induced at $26\text{--}28\text{ weeks of IUL}$.

Reflex pathways established age

Established between taste buds and facial expression muscles by the seventh month of IUL.

Caudal pharyngeal complex

The structure in humans formed by incorporating the fifth pouch into the fourth pouch.

Microglossia

A clinical condition where the tongue is abnormally small.

Macroglossia

A clinical condition where the tongue is abnormally large.

Frenulum linguae

The structure that anchors the tongue to the floor of the mouth.

Larynx, Trachea, Esophagus

Examples of possible sites for ectopic thyroid tissue.

Third arch mesoderm role

Grows over the second arch mesoderm to fuse with the first, burying the second arch.

Taste buds formation

Occurs during $11\text{--}12\text{ weeks of IUL}$ via inductive interaction.

Agenesis of tongue primordia

The embryological cause of rare aglossia.

In situ development

Mechanism by which some muscles of the tongue probably develop without migration.

Endodermal thickening

The first indication of thyroid development between the tuberculum impar and copula.

Thyroglossal duct path

Descends across the tongue, in front of the hyoid, then becomes retrohyoid.

Trigeminal nerve (Mandibular branch)

The nerve supplying the mucous membrane of the anterior $\frac{2}{3}$ of the tongue.

Second arch exclusion

The second arch is excluded from tongue development because it is buried by the third arch.

Occipital myoblasts migration

Explains the unique course of the hypoglossal nerve through the pharyngeal arches.

24 days after fertilization

The approximate time when the first indication of the thyroid gland appears.

Thyroid histogenesis

The process where epithelial cords divide into cell clusters to form follicles.

Isthmus absence

A possible anomalous shape of the thyroid gland.

Pyramidal lobe origin side

Usually arises on the left side of the upper aspect of the isthmus.

5 years of age

The age by which thyroglossal cysts are typically observed.

Midline of front of neck

The specific location where thyroglossal cysts are always formed.

Technetium-99m scan

A scan used to demonstrate sublingual thyroid location.

Infants with Down’s syndrome

Often characterize fissuring of the tongue and hypertrophy of lingual papillae.

Alveololingual sulcus

An endodermal sulcus that gradually separates the tongue from the primitive floor of the mouth.

Bitter tasting substances

Chemicals used to induce fetal facial responses at $26\text{--}28\text{ weeks of IUL}$.

Occult carcinoma size

A carcinoma of the thyroid gland with a diameter less than $1.5\,cm$.

Mandibular process structures

Lower lip, lower jaw, and tongue develop from this region.

Superior laryngeal nerve role

Supplies the mucous membrane of the posterior-most part of the tongue and epiglottis.

Glossopharyngeal nerve (CN IX)

The nerve of the third arch supplying the posterior $\frac{1}{3}$ of the tongue.

Thyroid tissue in 10% autopsies

The prevalence rate observed for lingual thyroid in autopsy studies.

Seventh week of IUL (Thyroid)

The time when the thyroid gland reaches its definitive position in the neck.

Cranial part of hypobranchial eminence

Forms the posterior $\frac{1}{3}$ of the tongue including circumvallate papillae.

Caudal part of hypobranchial eminence

Forms the posterior-most part of the tongue and the epiglottis.

Lingual swelling development

Develops soon after the tuberculum impar on each side of it.

Fusion of lingual swellings

The process that results in the overgrowth of the tuberculum impar.

Thyroid primordium network

Occurs when solid mass of cells is invaded by surrounding mesenchyme to form cords.

Colloid production timing

Starts at the end of the third month, approximately the 12th week of IUL.

C cells abbreviation

Stands for calcitonin-producing cells.

Suprahyoid thyroid

An ectopic thyroid location high in the neck above the hyoid bone.

Secondary opening on neck surface

Characteristic of a thyroglossal fistula after a cyst ruptures.

General sensation (Anterior Tongue)

Carried by the lingual nerve.

Special sensation/Taste (Anterior Tongue)

Carried by the chorda tympani nerve.

Nerve of the second arch

The facial nerve.

Thyroglossal duct persistence

The proximal opening persists on the tongue's dorsum as the foramen cecum.

Solid mass of endoderm

The initial composition of the thyroid primordium.

Gustatory nerve cells

Invading cells that interact with tongue epithelium to form taste buds.