Pharyngeal Apparatus PDF

Pharyngeal Apparatus by Dr. Afolayan Outline Description Components Derivatives Developmental Anomalies  DESCRIPTION: Pharyngeal Apparatus Also known as the branchial apparatus, meaning gills Formation starts on embryonic day 22 Involved in modeling and development of th...

Pharyngeal Apparatus by Dr. Afolayan Outline Description Components Derivatives Developmental Anomalies  DESCRIPTION: Pharyngeal Apparatus Also known as the branchial apparatus, meaning gills Formation starts on embryonic day 22 Involved in modeling and development of the cephalic end and face of the embryo Result in a complex form for the pharyngeal segment of the digestive tract. The lateral walls of the developing pharyngeal gut form the branchial system or apparatus Components of Pharyngeal apparatus Four components. Pharyngeal Arches Pharyngeal Grooves Pharyngeal Pouches Pharyngeal Membranes Pharyngeal Arches The first pharyngeal arch (mandibular arch) are masses of mesoderm covered by ectoderm and lined by endoderm. Within these masses, muscular and skeletal components develop, as well as aortic arches and nerve networks. The arches are separated by grooves, visible on the surface of the embryo as pharyngeal clefts and in the interior as the pharyngeal pouches = Meckel cartilage separates into two prominences : maxillary and mandibular prominences. Aortic Arch -Maxillary Artery 1st Pharyngeal Pouch –Auditory tube (eustachian tube) and tympanic cavity (distal end) 1st Pharyngeal Groove –External auditory meatus (exterior ear opening) Mandibular arch 2 prominences: Maxillary and Mandibular Maxillary Process: Cranial/Ventral -upper jaw Bone (intramembranous): 1. maxilla 2. zygomaticbone 3. squamouspart of the 4. temporal bone Mandibular arch MandibularProcess: Caudal/dorsal -lower jaw Cartilages -Meckel’scartilage -Malleus -Incus Bone -Mandible  The second pharyngeal arch (hyoid arch) -os hyoid, (along with parts of the third and fourth arches) During the fifth week, the second pharyngeal arch enlarges and overgrows the third and fourth arches, forming an ectodermal depression-the cervical sinus 2nd Aortic Arch -Hyoid artery, Stapedial artery 2nd Pharyngeal Pouch -Supratonsilar fossa –component of the palatine tonsils Hyoid Arch The third pharyngeal arch 🡪 greater cornu and the inferior part of the body 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 The third pharyngeal arch 3rd Aortic Arch –Internal Carotid artery 3rd Pharyngeal Pouch Dorsal -Paired inferior parathyroid, fuses with thyroid gland (parathyroid hormone, Calcium regulation). Ventral -hollow and elongate –fuses ventro-medially to form the bilobedthymus, secondarily moves posterior to become posterior to the thyroid gland (lymphocyte production, blood-thymic barrier). The fourth and the sixth pharyngeal arches Cartilages fuse to form laryngeal cartilages, except for the epiglottis. – 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. – 4th Aortic Arch –Right Subclavian artery, Aorta – 4th Pharyngeal Pouch – Dorsal -forms paired superiorparathyroids – Ventral -PostbranchialBody (ultimobranchial body, calcitonin)  The fifth pharyngeal arch is rudimentary (if present) and has no derivatives. The cartilage of the epiglottis develops from mesenchyme in the hypopharyngeal eminence, a prominence in the floor of the embryonic pharynx that is derived from the third and fourth pharyngeal arches. Musculature derived from the Pharyngeal arches Nerves Derive from the Pharyngeal Arches Cartilages derived from the pharyngeal arches Pharyngeal Pouches  PHARYNGEAL POUCHES Develop in a craniocaudal sequence between the arches 4 well-defined pairs of pharyngeal pouches; the 5th pair is rudimentary or absent. The endoderm of the pouches contacts the ectoderm of the pharyngeal grooves. A double-layered pharyngeal membranes separates the pharyngeal pouches from the pharyngeal grooves Pharyngeal pouches  The First Pharyngeal Pouch : Expands into an elongate tubotympanic recess The distal part of this recess contacts the first pharyngeal groove- the formation of the tympanic membrane (eardrum). The cavity of the tubotympanic recess --tympanic cavity & antrum mastoid The connection of the tubotympanic recess with the pharynx gradually elongates - pharyngotympanic tube (auditory tube). The Second Pharyngeal Pouch largely obliterated as the palatine tonsil develops, part of the cavity of this pouch remains as the tonsillar sinus or fossa. The pouch endoderm forms the surface epithelium and the lining of the tonsillar crypts. At approximately 20 weeks, the mesenchyme differentiates into  The Third Pharyngeal Pouch At 6th week, the epithelium of each dorsal part differentiate into an inferior parathyroid gland. The epithelium of the ventral parts come together in the median plane to form the thymus Each lobe has its own blood supply , lymphatic drainage, and nerve supply. Next : lose their connections with the pharynx.  During the expansion of brain and associated structures rostrally, the pharynx and cardiac structures generally expand caudally, the derivatives of pharyngeal pouches two to four to become displaced caudally. Later , the parathyroid glands separate from the thymus and lie on the dorsal surface of the thyroid gland The Fourth Pharyngeal Pouch At 6th week, each dorsal part: superior parathyroid gland, which lies on the dorsal surface of the thyroid gland. Ventral:ultimobranchial body, incorporated with thyroid, give rise to C cell (parafollicular cells) Pharyngeal pouches Pharyngeal pouches  Pharyngeal pouches superior parathyroid gland  PHARYNGEAL GROOVES/cleft Visible on each side during the fourth and fifth weeks. Separate the pharyngeal arches externally. Only one pair of grooves contributes to postnatal structures; the first pair persists as the external acoustic meatus or ear canals. The other grooves lie in a slitlike depression-the cervical sinus-and are normally obliterated along with the sinus as the neck. At the end of the 7th week, the second to fourth pharyngeal grooves and the cervical sinus have disappeared, giving the neck a smooth contour  PHARYNGEAL MEMBRANES As floors of the pharyngeal grooves. the epithelia of the grooves and pouches approach each other. The endoderm of the pouches and the ectoderm of the grooves are soon separated by mesenchyme. Only one pair of membranes contributes to the formation of adult structures; the first pharyngeal membrane, along with the intervening layer of mesenchyme, becomes the tympanic membrane.