1 DEVELOPMENT OF THE HEAD AND NECK G.LUFUKUJA

Head and neck  The mesenchyme for formation of the head region is derived from paraxial and lateral plate mesoderm, neural crest, and thickened regions of ectoderm known as ectodermal placodes. G.LUFUKUJA2

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4 Skeletal structure of skull; mesenchyme for these structures is derived from neural cells (blue star), and paraxial mesoderm (somites) (red), * * * * * *

Head and neck…  Paraxial mesoderm (somites)forms the floor of the brain case and a small portion of the occipital region; all voluntary muscles of the craniofacial region, the dermis and connective tissues in the dorsal region of the head, and the meninges caudal to the prosencephalon. G.LUFUKUJA5

PHARYNGEAL APPARATUS (Branchial arch) (Branchial arch  Neural crest cells originate in the neuroectoderm of forebrain, midbrain, and hindbrain regions and migrate ventrally into the pharyngeal arches and rostrally around the forebrain and optic cup into the facial region. In these locations they form mid-facial and pharyngeal arch skeletal structures  There are 5 pairs of branchial arches, that form on either side of the pharyngeal foregut on day 22 are the embryologic basis of all the differentiated structures of the head and neck 6G.LUFUKUJA

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9 Branchial arches

G.LUFUKUJA10 The Neural crest cells that originate in the neuro- ectoderm of forebrain, midbrain, and hindbrain regions form tissues that include cartilage, bone, dentin, tendon, dermis, pia and arachnoid, sensory neurons, and glandular stroma. PHARYNGEAL APPARATUS…

11 Derivatives of the first branchial arch cartilages  The first pharyngeal arch consists of a dorsal portion, the maxillary process, and a ventral portion, the mandibular process, which contains Meckel’s cartilage  During further development, Meckel’s cartilage disappears except for two small portions at its dorsal end that persist and form the incus and malleus G.LUFUKUJA

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 Mesenchyme of the maxillary process gives rise to the premaxilla, maxilla, zygomatic bone, and part of the temporal bone through membranous ossification  The mandible is also formed by membranous ossification of mesenchymal tissue surrounding Meckel’s cartilage G.LUFUKUJA13 Derivatives of the first branchial arch cartilages…

Musculature of the first pharyngeal arch  Musculature of the first pharyngeal arch includes the muscles of mastication (temporalis, masseter, and pterygoids), anterior belly of the digastric, mylohyoid, tensor tympani, and tensor palatini. G.LUFUKUJA14

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The nerve supply to the muscles of the first arch  The nerve supply to the muscles of the first arch is provided by the mandibular branch of the trigeminal nerve.  Since mesenchyme from the first arch also contributes to the dermis of the face, sensory supply to the skin of the face is provided by ophthalmic, maxillary, and mandibular branches of the trigeminal nerve.  Other derivatives  Mucous membrane and glands of the anterior two thirds of the tongue are derived from ectoderm and endoderm of the 1 st arch Mucous membraneanterior two thirds of the tongueectodermendoderm G.LUFUKUJA16

Derivatives of the second pharyngeal arch  The cartilage of the second or hyoid arch (Reichert’s cartilage) gives rise to the stapes, styloid process of the temporal bone, stylohyoid ligament, and ventrally, the lesser horn and upper part of the body of the hyoid bone. G.LUFUKUJA17

Muscles of the 2 nd arch  Muscles of the hyoid arch are the stapedius, stylohyoid, posterior belly of the digastric, auricular, and muscles of facial expression.  The facial nerve, the nerve of the second arch, supplies all of these muscles. G.LUFUKUJA18

THIRD PHARYNGEAL ARCH  The cartilage of the third pharyngeal arch produces the lower part of the body and greater horn of the hyoid bone. The musculature is limited to the stylopharyngeus muscles. These muscles are innervated by the glossopharyngeal nerve, the nerve of the third arch G.LUFUKUJA19

FOURTH AND SIXTH PHARYNGEAL ARCHES  Cartilaginous components of the fourth and sixth pharyngeal arches fuse to form the thyroid, cricoid, arytenoid, corniculate, and cuneiform cartilages of the larynx. G.LUFUKUJA20

FOURTH AND SIXTH PHARYNGEAL ARCHES  Muscles of the fourth arch (cricothyroid, levator palatini, and constrictors of the pharynx) are innervated by the superior laryngeal branch of the vagus, the nerve of the fourth arch.  Intrinsic muscles of the larynx are supplied by the recurrent laryngeal branch of the vagus, the nerve of the sixth arch. G.LUFUKUJA21

PHARYNGEAL POUCHES  The human embryo has five pairs of pharyngeal pouches. The last one of these is atypical and often considered as part of the fourth.  Since the epithelial endodermal lining of the pouches gives rise to a number of important organs, the fate of each pouch is discussed separately. G.LUFUKUJA22

FIRST PHARYNGEAL POUCH  The first pharyngeal pouch forms a stalklike diverticulum, the tubotympanic recess, which comes in contact with the epithelial lining of the first pharyngeal cleft, the future external auditory meatus. G.LUFUKUJA23

FIRST PHARYNGEAL POUCH…  The distal portion of the diverticulum widens into a saclike structure, the primitive tympanic or middle ear cavity, and the proximal part remains narrow, forming the auditory (eustachian) tube. The lining of the tympanic cavity later aids in formation of the tympanic membrane or eardrum G.LUFUKUJA24

SECOND PHARYNGEAL POUCH  The epithelial lining of the second pharyngeal pouch proliferates and forms buds that penetrate into the surrounding mesenchyme. The buds are secondarily invaded by mesodermal tissue, forming the primordium of the palatine tonsil. During the third and fifth months, the tonsil is infiltrated by lymphatic tissue. Part of the pouch remains and is found in the adult as the tonsillar fossa. G.LUFUKUJA25

THIRD PHARYNGEAL POUCH  In the fifth week, epithelium of the dorsal wing of the third pouch differentiates into the inferior parathyroid gland, while the ventral wing forms the thymus.  Both gland primordia lose their connection with the pharyngeal wall, and the thymus then migrates in a caudal and a medial direction, pulling the inferior parathyroid with it. G.LUFUKUJA26

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 Epithelium of the dorsal wing of the fourth pharyngeal pouch forms the superior parathyroid gland. When the parathyroid gland loses contact with the wall of the pharynx, it attaches itself to the dorsal surface of the caudally migrating thyroid as the superior parathyroid gland G.LUFUKUJA29 FOURTH PHARYNGEAL POUCH

 The fifth pharyngeal pouch, the last to develop, is usually considered to be a part of the fourth pouch. It gives rise to the ultimobranchial body, which is later incorporated into the thyroid gland. Cells of the ultimobranchial body give rise to the parafollicular, or C, cells of the thyroid gland. These cells secrete calcitonin, a hormone involved in regulation of the calcium level in the blood. G.LUFUKUJA30 FIFTH PHARYNGEAL POUCH

 The 5-week embryo is characterized by the presence of four pharyngeal clefts, of which only one contributes to the definitive structure of the embryo. The dorsal part of the first cleft penetrates the underlying mesenchyme and gives rise to the external auditory meatus. G.LUFUKUJA31 Pharyngeal Clefts The epithelial lining at the bottom of the meatus participates in formation of the eardrum

G.LUFUKUJA32 Pharyngeal Clefts

 Active proliferation of mesenchymal tissue in the second arch causes it to overlap the third and fourth arches. Finally, it merges with the epicardial ridge in the lower part of the neck, and the second, third, and fourth clefts lose contact with the outside.  The clefts form a cavity lined with ectodermal epithelium, the cervical sinus, but with further development this sinus disappears. G.LUFUKUJA33 2 nd Pharyngeal Clefts

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35 Branchial cysts/sinus G.LUFUKUJA

Development of the Tongue  The adult tongue is derived from embryonic processes arising from the first three pharyngeal arches and a small contribution from the fourth arch.  The anterior two thirds of the adult tongue (the movable part) is formed by two lateral swellings and a single one, the tuberculum impar, all of which are derived from the first pharyngeal arch 36G.LUFUKUJA

Development of the Tongue…  The posterior third (the fixed part or the root of the tongue) is formed by an embryonic process, the hypobranchial eminence or copula. This process is derived mainly from the second and third pharyngeal arches with small part from the fourth pharyngeal arch.  The muscles of the tongue are derived from a different embryonic source, namely the occipital myotomes. 37G.LUFUKUJA

38 Development of the Tongue

Development of the Tongue…  The junction of the anterior 2/3 and the posterior 1/3 of the adult tongue is marked by a V-shaped structure, the sulcus terminalis and at its tip is a blind foramen, the foramen caecum. This site marks the area from which an epithelial structure arise during embryonic development and extend inferiorly to the anterior part of the future neck where it forms the thyroid gland. 39G.LUFUKUJA

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Tongue tie  Medically defined as having ankyloglossia, is a condition in which the lingual frenulum (a membrane that connects the tongue to the floor of the mouth G.LUFUKUJA41

Development of the pituitary gland  Just anterior to the buccopharyngeal membrane, a midline diverticulum known as the Rathke pouch develops in the oral ectoderm of the roof of the primitive oral cavity.  This evaginating pouch comes in contact with a pouch developing from the floor of the diencephalon. Further development of these two opposed structures gives rise to the pituitary gland. G.LUFUKUJA42

G.LUFUKUJA43 Development of the pituitary gland…

G.LUFUKUJA44 Development of the pituitary gland…

Rathke cleft cyst  A Rathke's cleft cyst is a benign growth found on the pituitary gland in the brain, specifically a fluid-filled cyst in the posterior portion of the anterior pituitary gland. It occurs when the Rathke's pouch does not develop properly, and ranges in size from 2 to 40mm in diameter pituitary glandcystRathke's pouch  If a cyst adds pressure to the optic chiasm, it may cause visual disturbances, pituitary dysfunction, and headaches G.LUFUKUJA45

Thyroid Gland  The thyroid gland appears as an epithelial proliferation in the floor of the pharynx between the tuberculum impar and the copula at a point later indicated by the foramen cecum. 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 a narrow canal, the thyroglossal duct. G.LUFUKUJA46

G.LUFUKUJA47 Thyroglossal cyst/ thyroglossal fistula.

Lingual thyroid G.LUFUKUJA48

49 The Face  The face is formed from 7 primordia surrounding the stomodeum  Single frontonasal prominence -cranial boundary of the stomodeum  Paired median nasal process  Paired maxillary process  Paired mandibularprocess G.LUFUKUJA

50 Derivatives of the branchial arch cartilages  When the embryo is 42 days old, five mesenchymal prominences can be recognized: the mandibular prominences (first pharyngeal arch), caudal to the stomodeum; the maxillary prominences (dorsal portion of the first pharyngeal arch), lateral to the stomodeum; and the frontonasal prominence, a slightly rounded elevation cranial to the stomodeum. G.LUFUKUJA

51 Development of the Face…  The Frontonasal prominence forms the forehead. The nasal prominence is split into lateral and medial nasal processes by formation of a nasal placode  Thus a horseshoe-shaped nasal processes surrounds the nasal placode, which undergoes apoptosis to form a depression; the nasal pit. Initially, the maxillary and lateral nasal prominences are separated by a deep furrow, the nasolacrimal groove.  Ectoderm in the floor of this groove forms a solid epithelial cord that detaches from the overlying ectoderm. After canalization, the cord forms the nasolacrimal duct; its upper end widens to form the lacrimal sac. G.LUFUKUJA

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Intermaxillary segment  As a result of medial growth of the maxillary prominences, the two medial nasal prominences merge not only at the surface but also at a deeper level. The structure formed by the two merged prominences is the intermaxillary segment G.LUFUKUJA53

G.LUFUKUJA54 labial component,upper jaw component,palatal component,

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Secondary Palate  These are outgrowths, the palatine shelves, appear in the sixth week of development and are directed obliquely downward on each side of the tongue G.LUFUKUJA56

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58 Anomalies  Craniofacial: These are defects associated with tissue fusion. Estimated 1/3 of all congenital defects are craniaofacial  Facial Clefts - Anomalies associated with defective fusion of Facial prominences  1. Cleft lip - failure of maxillary prominence to fuse with intermaxillary process  2. Cleft palate - failure of the lateral palatine processes to fuse G.LUFUKUJA

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Paranasal air sinuses  develop as diverticula of the lateral nasal wall and extend into the maxilla, ethmoid, frontal, and sphenoid bones. G.LUFUKUJA61

Thank you 62G.LUFUKUJA