Embryology 7: Development of Tongue and Anomalies PDF

EMBRYOLOGY 7 Dr.Ban A.Ghani DEVELOPMENT OF TONGUE AND ANOMALIE The tongue is a muscular structure located on the floor of the oral cavity.It is the primary taste organ and plays a key role in the initial phases of swallowing. Embryologically, the...

EMBRYOLOGY 7 Dr.Ban A.Ghani DEVELOPMENT OF TONGUE AND ANOMALIE The tongue is a muscular structure located on the floor of the oral cavity.It is the primary taste organ and plays a key role in the initial phases of swallowing. Embryologically, the development of tongue is a very complicated process that starts around the 4th week of the gestation period, and its development has a marked influence on the oral cavity. The development begins with the growth of a medial swelling from the 1st pharyngeal arch, known as tuberculum impar. Gradually, two lateral lingual swellings start to grow in the 5 th week from the same arch. As the lateral swellings increase in size, they eventually merge and overlap tuberculum impar. This merging leads to the formation of the anterior 2/3rd of the tongue. Since the mucosa overlying this area of the tongue has its origin from the 1st pharyngeal arch; it receives its sensory innervation from the mandibular branch of the V cranial nerve (trigeminal nerve). From the mesoderm of the 2nd , 3rd , and 4th pharyngeal arches, another median swelling, known as hypobranchial eminence(copula which is overgrown by the 3rd and 4th arches) begins to develop and form the posterior 3rd of the tongue. The mucosa overlying this area of the tongue receives its sensory innervation from the IX cranial nerve (glossopharyngeal nerve). The posterior-most part of the tongue develops from a third median swelling form the epiglottis, arising from the 4th pharyngeal arch. This area of the tongue receives its innervations from the superior laryngeal nerve. EMBRYOLOGY 7 Dr.Ban A.Ghani OCCIPITAL SOMITES (MUSCULATURE) The connective tissue component, as well as vasculature of the tongue, is derived from cranial neural crest cells (CNCC). These cells initiate the formation of the tongue bud and the interstitial connective tissue. The myoblasts which are responsible for the formation of the muscle components of the tongue derive from the occipital somite which are segments of mesoderm in the region of the upper neck.. Cells from this somite migrate into the primordium of the tongue, thus, forming the muscle cells in the tongue ,they receive their innervations from the XII cranial nerve (hypoglossal nerve) except the palatoglossus muscle. EMBRYOLOGY 7 Dr.Ban A.Ghani TONGUE ANOMALIE Some of the various morphological variations that may occur during the development of tongue are: AGLOSSIA: Congenital absence of the tongue is extremely rare. Usually, the tongue is absent in cases of gross underdevelopment or maldevelopment of the first pharyngeal arches. EMBRYOLOGY 7 Dr.Ban A.Ghani MICROGLOSSIA: It is an uncommon developmental condition and is also known as hypoglossia. Its defining feature is a rudimentary or an abnormally small tongue. It leads to limited muscular movement. MACROGLOSSIA: is an infrequently encountered condition characterized by tongue enlargement, seen in association with other congenital defects leading to syndromes such as down syndrome (trisomy 21). ANKYLOGLOSSIA: It occurs due to failure in cellular degeneration leading to anchorage between the tongue and floor of the mouth; this is commonly known as "tongue-tied" and demonstrates an abnormally short lingual frenulum. Ankyloglossia can range in severity from mild to complete ankyloglossia in which the tongue gets fused to the floor of the mouth restricting its free movement. EMBRYOLOGY 7 Dr.Ban A.Ghani CLEFT TONGUE: It is also known as bifid tongue and occurs when the lateral swellings fail to merge. It can be partial or complete. The former is manifested as a deep groove on the dorsal surface of the tongue in the midline. It occurs when the mesenchymal proliferation interferes with the merging leading to failure of the obliteration of the groove. GEOGRAPHIC TONGUE: also known as benign migratory glossitis is an inflammatory disorder caused by loss of filiform papillae. EMBRYOLOGY 7 Dr.Ban A.Ghani