General information

2. EMBRYONIC DEVELOPMENT OF THE TONGUE

3. The tongue: Is a muscular organ of the oral cavity and is an
accessory digestive organ in the digestive system. The tongue
has a very rich neurovascular supply, and its importance in
humans is tightly connected to the digestive system and
speech.
THE TONGUE
- MUSCULAR STRUCTURE
- SENSORY ORGAN

4. Function of the tongue:
- Mastication
- Swallowing
- Taste
- Speech

5. Development of the tongue
The tongue begins development in the 4th
week of gestation
(pregnancy). It is derived from the 4 pharyngeal arches 1-4
(forms the mucosa of the tongue) and the occipital somites
(forms the musculature of the tongue).

6. A fully developed tongue consists of two parts:
- Anterior 2/3
- Posterior 1/3 ( root of the tongue)

7. They are separated from each other by a shallow V-shaped
groove called a terminal sulcus
Terminal sulcus

8. In the first stage of development, lateral and medial swellings appear:
 Two lateral lingual swellings– derived from the 1st pharyngeal arch contribute
to the mucosa of the anterior 2/3rd of the tongue
 Three medial swellings :
o Tuberculum impar – derived from the 1st pharyngeal arch, contributes to
the mucosa of the anterior 2/3rd of the tongue.
o Cupola (hypobranchial eminence) –derived from the 2nd , 3rd and 4th
pharyngeal arches. Forms the mucosa of the posterior 1/3rd of the tongue.
o Epiglottal swelling – derived from the 4th pharyngeal arch. Forms the
epiglottis.

9. Anterior 2/3 of the tongue develops from first pharyngeal arch
Posterior 1/3 of the tongue develops from 2nd
, 3rd
, and 4th
pharyngeal
arch

10. Anterior 2/3 starts developing when the mesoderm of the 1st
pharyngeal arch proliferates giving rise to midline swelling called
Tuberculum impar. During the following week, the mesoderm of the
same arch gives rise to two lateral swellings called right and left
lateral lingual swellings just lateral and above the tuberculum impar.
Lateral lingual swellings enlarge and overlap tuberculum impar and
merge with each other along the midline giving rise the mucosa over
the anterior 2/3 of the tongue. Their line of fusion called median
sulcus of the tongue.
Development of anterior 2/3 of the tongue

12. Development of posterior 1/3 of the tongue
The posterior 1/3 of the tongue also begins to develop around week
4 as a medial swelling called copula (hypobranchial eminence).
Which is derived from 2nd
, 3rd
and 4th
pharyngeal arches. Forms the
mucosa of the posterior 1/3 of the tongue. Then the mucosa of the
posterior 1/3 of the tongue fuses with the anterior 2/3 and forms a
complete tongue.

13. The region between anterior 2/3 and posterior 1/3 contains a V
shaped depression called terminal sulcus. At the tip of the terminal
sulcus the endoderm develops downward into thyroid gland. The
decend of the endoderm creats tiny sac called Foramen cecum.
Foramen cecum represents the origin of the thyroid gland.

14. Development of the musculature of the tongue
Occipital somites Myoblasts Tongue skeletal muscles
Occipital Somites (Musculature)
The intrinsic and extrinsic muscles of the tongue are derived from
occipital somites, which are segments of mesoderm in the region of
the upper neck. The somites migrate from the neck anteriorly to give
rise to the muscles of the tongue.

15. The occipital somites that come from paraxial mesoderm migrate into
the developing tongue, the occipital somites give rise to myoblasts
and then develop into tongue skeletal muscles

16. Taste buds
After the complete development of mucosa and musculature of the tongue, taste
buds start to spread over the surface of the tongue around week 8 and finish
differentiating into different types around week 11-13.
Cells of the taste bud are derived from epithelial lineages but are
specialized to perform gustatory functions.

17. Vasculature
The lingual artery (branch of the external carotid) does most of the
supply, but there is a branch from the facial artery, called the
tonsillar artery, which can provide some collateral circulation.
Drainage is by the lingual vein.

18. Nerve supply
The functional components of the tongue are:
- Motor
- Sensory.
The motor component refers to the muscles of the tongue,
whereas the sensory component is associated with the
structures called lingual papillae which contain taste
receptors.

19. Innervation of the anterior 2/3
-Sensory innervation of the mucosa is via the lingual branch
of the trigeminal nerve
-Taste bud innervation is via the chorda tympani branch of
the facial nerve
-The taste buds in the circumvallate papilla that present in
the posterior most of the of the anterior 2/3 of the tongue are
innervated by glossopharyngeal nerve.

20. Innervation of the posterior 1/3
- Sensory innervation of the mucosa is mostly via the
glossopharyngeal nerve (and some vagus)
-Taste innervation is mostly via the glossopharyngeal nerve (and some
vagus)
Motor innervation of the tongue
Hypoglossal nerve (CN XII) provides motor innervation to all of the
interensic and extrinsic muscles of the tongue , except for the
palatoglossus muscle which is innervated by the vagus nerve

21. Lingual papillae: are small structures
on the upper surface of the tongue that
give it its characteristic rough
texture. The four types of papillae on
the human tongue have different
structures and are accordingly classified
as circumvallate (or vallate), fungiform,
filiform, and foliate. All except the
filiform papilla are associated with taste
buds.

22. Developmental (congenital) disorders
Most developmental disorders of the tongue are related to its size and
shape, though structural defects also exist. Some of the developmental
disorders are:
1- Microglossia
2- Macroglossia
3- Ankyloglossia

23. Microglossia This is a rare condition where the size of the
tongue is abnormally small. Cases of complete absence of the
tongue have been reported. A tiny tongue will pose many
difficulties related to speech and swallowing. There is no
treatment for this condition, and the affected person will have
to train their tongue to the best of their abilities.

24. Microglossia

25. Macroglossia
Macroglossia is the medical term for an unusually large tongue. Sever
enlargement of the tongue can cause cosmetic and functional difficulties in
speaking, eating, swallowing and sleeping. There are many causes can be
associated with a number of genetic abnormalities including: trisomy 21
(Down syndrome), acromegaly. Treatment is dependent upon the exact cause.

26. Ankyloglossia (Tongue-Tie)
Ankyloglossia (tongue-tie) is the general clinical term for the short lingual
frenulum (less than 2 cm), that limits the range of movement of the tongue,
This is associated with speech development and feeding disorders. In the most
common form of ankyloglossia, the frenulum extends to the tip of the tongue.

27. Thyroid gland
The thyroid, or thyroid gland, is an endocrine gland in
vertebrates. In humans it is in the neck and consists of two
connected lobes. The lower two thirds of the lobes are
connected by a thin band of tissue called the thyroid
isthmus. The thyroid is located at the front of the neck,
below the Adam's apple

28.  The thyroid gland appears as an epithelial proliferation at a
point indicated by the foramen ceacum . Subsequently, the
thyroid descends in front of the pharyngeal gut as a bilobed
diverticulum .
 During this migration, the thyroid remains connected to the
tongue by the thyroglossal duct which later disappears.
 With further development, the thyroid gland descends in
front of the hyoid bone and the laryngeal cartilages. It reaches
its final position in front of the trachea in the 7 th week.

29.  The thyroid begins to function at approximately the end of
the third month, at which time the first follicles containing
colloid become visible.
 Follicular cells produce the colloid that serves as a source
of:
Triiodothyronine(T3)
Thyroxine (T4)
Parafollicular, or C, cells derived from the ultimobranchial
body(derived from (4th pharyngeal pouch) , serve as a source
of calcitonin.

30. Thyroglossal duct cyst
A thyroglossal duct cyst is a congenital anomaly it’s a mass
or lump in the front part of neck that is filled with fluid.
Thyroglossal cysts are the most common cause of midline
neck masses and are generally located caudal to (below) the
hyoid bone. These neck masses can occur anywhere along
the path of the thyroglossal duct, from the base of the tongue
to the suprasternal notch. A thyroglossal cyst may lie at any
poínt along the migratory pathway of the thyroid gland but
is always near or in the midline of the neck.

31. It is a cystic remnant of the thyroglossal duct,they may also
be found at the base of the tongue or close to the thyroid
cartilage.Sometimes, a thyroglossal cyst is connected to the
outside by a fistulous canal, a thyroglossal fístula. Such a
fistula usually arises secondarily after rupture of a cyst but
may be present at birth.