Development of the Tongue and Thyroid Gland PDF

DEVELOPMENT OF THE TONGUE AND THYROID GLAND MOHD ASIM KHAN ASSISTANT PROFESSOR- KKU (KSA) [email protected]...

DEVELOPMENT OF THE TONGUE AND THYROID GLAND MOHD ASIM KHAN ASSISTANT PROFESSOR- KKU (KSA) [email protected] LEARNING OBJECTIVES ▪ At the end of this lecture, the students should be able to: 1. Describe the development of the tongue and correlate the nerve supply of tongue with its development 2. Describe congenital anomaly associated with the tongue: Tongue-tie 3. Describe the embryology of the thyroid gland in brief and discuss its histogenesis 4. Describe the embryological basis of: 1. Ectopic thyroid gland  DEVELOPMENT OF THE TONGUE ▪ ORAL PART (ANTERIOR TWO-THIRDS) OF THE TONGUE: Forms from 1. One median swelling (Tuberculum Impar) - First indication of tongue development 2. Two lateral lingual swellings These three swellings originate from the first pharyngeal arch in the floor of the pharynx just rostral to the foramen caecum due to proliferation of mesoderm near the end of the fourth week 3. The lateral lingual swellings rapidly increase in size, merge with each other, and overgrow the median tongue swelling The merged lateral swellings form the anterior two thirds (oral part) of the tongue Tuberculum = Small eminence or tubercle Impar = Being an unpaired anatomical part Ventral portion of the pharyngeal arches seen from above at week 5 Reference: Medical Embryology By Langman, 13th Edition  DEVELOPMENT OF THE TONGUE P ▪ PHARYNGEAL PART (POSTERIOR ONE-THIRD) OF THE TONGUE P Indicated by two elevations that develop caudal to the foramen cecum in the floor of the pharynx due to a proliferation of mesoderm associated with pharyngeal arches 2, 3, and 4 1. COPULA Copula derives from the Latin noun for a "link" ▪ Formed by second pair of pharyngeal arches or "tie" that connects two different things 2. HYPOPHARYNGEAL EMINENCE (=HYPOBRANCHIAL EMINENCE) ▪ Develops caudal to the copula from third and fourth pairs of the pharyngeal arches Schematic horizontal sections through the pharynx showing successive stages in the development of the tongue during the fourth and fifth weeks Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition  DEVELOPMENT OF THE TONGUE PHARYNGEAL PART (POSTERIOR ONE-THIRD) OF THE TONGUE 1. The copula (pharyngeal arch 2) is overgrown by the hypobranchial eminence (pharyngeal arches 3 and 4) and disappears 2. As a result, the pharyngeal part of the tongue develops from the rostral part of the hypobranchial eminence thereby eliminating oralpart sp any contribution of the copula (pharyngeal arch 2) in the formation of the definitive Scheme to show how the second arch is buried by adult tongue overgrowth of the third arch, during development of the tongue Reference: Human Embryology, By Inderbir Singh, 11th edition  DEVELOPMENT OF THE TONGUE The line of fusion between the oral and pharyngeal parts of the tongue is indicated by the terminal sulcus Drawings of the adult tongue Dorsum of the adult tongue Reference: Color Atlas of Clinical Embryology, By Moore, 2nd Edition Reference: Lippincott’s Concise Illustrated Anatomy- Head and Neck (Volume 3) By Pansky and Gest  SUMMARY OF THE DERIVATION OF COMPONENTS OF THE TONGUE ADULT COMPONENT EMBRYONIC GENERAL SENSATION SPECIAL SENSATION COMPONENT (Pain, Temperature) (TASTE APPRECIATION) 1. Mucosa of anterior 2/3 1st arch Lingual nerve Chorda tympani (Oral part) (Mandibular division of (Facial nerve, CN VII) 2. Epithelium 3. Connective tissue trigeminal nerve, CN V3) I I Except vallate papillae 1. Mucosa of posterior 1/3 3rd arch Glossopharyngeal nerve, CN IX (Pharyngeal part) 2. Epithelium I Includes vallate papillae 1 3. Connective tissue 1. Posterior most near vallecula 4th arch Superior laryngeal nerve 2. Epithelium (Vagus nerve, CN X) 3. Connective tissue sensory oh Muscles Myoblasts migrating MOTOR NERVE 1. Intrinsic muscles from occipital somites All muscles of the tongue are supplied by the hypoglossal 2. Extrinsic muscles …………………………………… nerve (XII) except palatoglossus which is supplied from the Palatoglossus pharyngeal plexus by fibers arising from the vagus nerve From mesoderm of 4th pharyngeal arch  DEVELOPMENT OF THE TONGUE MUSCLES OF THE TONGUE All the muscles of the tongue except the palatoglossus are formed by mesoderm derived from myoblasts that migrate into the tongue region from occipital somites Reference: Netter’s Atlas of Human Embryology, By Cochard, 1st edition  DEVELOPMENT OF THE THYROID GLAND 1. First endocrine gland to develop 2. The thyroid primordium first forms late in the fourth week and appears as a small, solid mass of endodermal proliferating at the apex of the foramen cecum on the developing tongue Cecum (or Caecum): Latin, blind A primordium (Plural, primordia) is an organ or tissue in its earliest recognizable stage of development Ventral portion of the pharyngeal arches seen from above showing development of the tongue. I to IV, the cut pharyngeal arches. A. 5 weeks (6 mm). B. 5 months. Note the foramen cecum, site of origin of the thyroid primordium Reference: Medical Embryology By Langman, 13th Edition  DEVELOPMENT OF THE THYROID GLAND 3 1. The thyroid primordium descends in front of the pharyngeal gut as a bilobed thyroid diverticulum Ñw Is ok Diverticulum: Pouch or sac opening from a hollow organ 1 2 Note the foramen cecum, site of origin of the thyroid primordium A to D: Stages in the development of the thyroid gland Midsagittal view of embryo at 4 to 5 weeks Reference: Human Embryology, By Inderbir Singh, 11th edition Reference: Netter’s Atlas of Human Embryology, By Cochard, 1st edition  DEVELOPMENT OF THE THYROID GLAND 2. During this migration, the thyroid remains connected to the tongue by a narrow canal, the thyroglossal duct 3. The thyroglossal duct breaks down by the end of the fifth week and disappears, but may persist as pyramidal lobe or thyroglossal cyst Fig.1 4. The site of the thyroglossal duct is indicated in the adult by the foramen cecum Thyr/o + Glossal (of the tongue) A B c D 1. The thyroid originates as an endodermal proliferation at the tip of the foramen cecum of the developing tongue and migrates inferiorly to its final site anterior and inferior to the larynx 2. Until the fifth week, the thyroid remains connected to the foramen cecum by the thyroglossal duct 3. The gland reaches its final site in the seventh week Arrow indicates the direction of migration of the developing thyroid gland Reference: Human Embryology, By Larsen, 5th edition  DEVELOPMENT OF THE THYROID GLAND 5. With further development, the thyroid gland descends in front of the hyoid bone (behind which it later forms a recurrent loop) and the laryngeal cartilages 6. The thyroid gland reaches its final position in front of the trachea in the seventh week and has acquired a small median isthmus and two lateral lobes i.e., assumed its definitive shape MNEMONIC DEVICE THYROID= 7 Alphabets = Week 7 A C B D Path taken by the thyroid gland during its embryological descent Development of the thyroid gland (indicated by the former tract of the thyroglossal duct Reference 1 : Human Embryology, By Larsen, 5th edition Reference 2: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition  DEVELOPMENT OF THE THYROID GLAND 1. The endoderm of the thyroid primordium differentiates into the thyroid follicular cells 2. The thyroid begins to function at approximately the end of the third month at which time the first follicles containing colloid become visible see 3. Follicular cells produce the colloid that serves as a source of thyroxine and triiodothyronine 1 2 4. Thyroid function is necessary for proper Thyroid gland organization Embryology of the thyroid brain development 1. Reference: Lippincott Illustrated Reviews – Physiology, By Preston and Wilson, 2nd Edition 2. Reference: Lippincott Illustrated Reviews – Anatomy, By Harrell and Dudek, 1st Edition Note: The thyroid gland begins to secrete hormone as early as weeks 10-12 The colloid begins to appear in the thyroid follicles at week 11  DEVELOPMENT OF THE THYROID GLAND 1 2 Fig. A Embryo at 4 to 5 weeks PHARYNX (ANTERIOR VIEW OF LEFT SIDE) Reference: Netter’s Atlas of Human Embryology, By Cochard, 1st edition EMBRYOLOGY OF THE THYROID GLAND THYROID GLAND ORGANIZATION 1. Reference: Lippincott Illustrated Reviews – Anatomy, By Harrell and Dudek, 1st Edition 2. Reference: Lippincott Illustrated Reviews – Physiology, By Preston and Wilson, 2nd Edition Neural crest cells within the ultimopharyngeal body, i.e.,pharyngeal pouch 4 (ultimobranchial body) disperse throughout the thyroid gland and differentiate into the parafollicular cells (or C cells) Parafollicular cells of thyroid gland serve as a source of (or secrete) calcitonin, a hormone involved in regulation of the calcium level in the blood  THYROID GLAND - CLINICAL NOTES ▪ ECTOPIC THYROID GLAND 1. Located along the normal route of its descent from the tongue 2. Lingual thyroid glandular tissue (most common type) 3. Sublingual thyroid gland (high in neck, at or just inferior to hyoid bone) f Ectopic= Occurring in an abnormal position 1 2 The head and neck, showing the usual sites of the ectopic thyroid tissue The broken line indicates the path followed by the thyroid gland during its descent, as well as the former tract of the thyroglossal duct Position of the thyroid gland in the adult Broken line, the path of migration Reference: Medical Embryology by Langman, 13th Edition Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition