development of, tongue, thyroid, sinus and salivary …...developmental anomalies •macroglossia...
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Development of, tongue, thyroid, sinus and salivary glands
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Development of tongue
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• 1st ,2nd, 3rd, 4th pharyngeal arches
• Median swelling- tuberculum impar
• Two lateral swellings –lingual
• Caudal medial swelling- hypobrachialeminence
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Anterior 2/3 of the tongue:
• Formation: median and lateral tongue buds that arise from the floor of the 1st pharyngeal archand then grow rostrally.
• thus it is formed by fusion of --• tuberculum impar , • two lingual swellings • The tongue buds are then invaded by occipital
myoblasts that form the intrinsic muscles of the tongue.
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• Thus anterior 2/3rd of tonguer is supplied by lingual branch of mandibular nerve ,(post trematic nerve of this arch) and chordatympani nerve( pretrematic nerve of arch)
• posterior 1/3rd of tongue is supplied by glossopharyngeal nerve ( nerve of 3rd arch)
• Most posterior 1/3rd of tongue is supplied by superior laryngeal nerve ( nerve of 4th
arch)
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• Musculature of tongue is derived from occipital myotomes --explains nerve supply by hypoglossal nerve, nerve of these myotomes.
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Posterior 1/3rd of tongue
• formed from cranial part of hypobranchialeminence ( copula)
• the second arch mesoderm gets buried below the surface .
• the third arch mesoderm grows over it to fuse with mesoderm of first arch .
• posterior one third of tongue thus formed by third arch mesoderm.
• posterior most part of tongue is derived from fourth arch
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• Thus swellings from the floor of the 3rd and 4th pharyngeal arches overgrow the 2nd arch and fuse with the anterior 2/3 of the tongue.
• posterior 1/3 of the tongue is derived from the 3rd and 4th arches
• Intrinsic musculature is also derived from occipital myoblasts.
• The line of fusion of the anterior 2/3 and posterior 1/3 of the tongue is indicated by the terminal sulcus.
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Developmental anomalies
• Macroglossia• microglossia• Median rhomboid glossitis : smooth red rhomboidal zone
of the tongue in front of foramen ceacum due to persistence of tuberculum impar
• Ankyloglossia• Bifid tongue: due to failure in the fusion of the 2
lateral lingual prominences.• Thyroid gland may be persist at the base of the
tongue.• Part of the thyroglossal duct may persist at the
base of the tongue & lead to cyst formation
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Development of thyroid
• thyroid median endodermal thickening in the floor of pharynx, outpouch – thyroid diverticulum
• tongue grows, cells descend in neck
• thyroglossal duct - proximal end at the foramen cecum of tongue thyroglossal duct
• thyroid diverticulum - hollow then solid, right and left lobes, central isthmus
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