Embryology II.pdf

Embryology II Pharyngeal Apparatus 24-28 day old Embryonic structure Key for development of head and neck Three components: o Pharyngeal clefts (ectoderm) o Pharyngeal arches (mesoderm) o Pharyngeal pouches (endoderm) Pharyngeal Arches Pharyngeal arches derived from mesoderm Each pharyngeal arch giv...

Embryology II Pharyngeal Apparatus 24-28 day old Embryonic structure Key for development of head and neck Three components: o Pharyngeal clefts (ectoderm) o Pharyngeal arches (mesoderm) o Pharyngeal pouches (endoderm) Pharyngeal Arches Pharyngeal arches derived from mesoderm Each pharyngeal arch gives rise to: o Cartilage element o Muscular element o Vascular element o Nervous element Cartilage Nerve Max. Process Maxilla Zygomatic bone Mand. Process Mandible Meckel’s Cartilage (incus, malleus) Pharyngeal Arches Muscle Vessel CN V (5) Chew Muscles of Mastication (Temporalis, Masseter, pterygoids) Anterior Digastric Mylohyoid Tensor Tympani (middle ear) Maxillary Artery 2nd Arch Reichert’s Cartilage Stapes (mid ear) Styloid Process Hyoid (Lesser horn) CN VII (7) Smile Stapedius (ear) Auricular (ear) Stylohyoid Posterior digastric Muscles of facial expression Stapedial Artery Embryonic vessel Involuted in development Hyoid Artery Embryonic vessel Develops into Small branch of internal carotid 3rd Arch Hyoid (Greater horn) CN IX (9) Swallow Stylopharyngeus Common carotid Proximal internal carotid artery 4th 6th Arch (Fused) Larynx Cartilage Thyroid Arytenoid Cricoid Corniculate Cuneiform CN X (10) Swallow Speak Laryngeal muscles 4th Cricothyroid Levator Palatini Pharyngeal constrictors 6th All intrinsic muscles of larynx except cricothyroid 1st Arch ** No 5th arch in humans 4th L: aortic arch R: right subclavian 6th (pulmonary arch) L pulmonary artery, ductus arteriosus R pulmonary artery 1st arch: forms the face. The rest of the arches form the neck Treacher Collins Syndrome First arch syndrome Failure of neural crest cell migration Mutation TCOF1, POLR1C, POLR1D Underdeveloped facial bones o Small mandible (mandibular hypoplasia) o Small jaw (micrognathia) o Absent/small ears o Glossoptosis (retraction of tongue) May lead to difficulty breathing o Underdeveloped lower jaw o Obstruction of airway by tongue Tongue During 4th week, tongue appears as two lateral lingual swellings and one medial this is called Tuberculum impar Anterior two-thirds: 1st and 2nd arches o Sensation: CN V-5 (1st arch) o Taste: CN VII-7 (2nd arch) Posterior third: 3rd and 4th arches o Sensory: CN IX-9 (3rd arch) o Some posterior taste CN X (4th arch) Pharyngeal Pouches 4 pouches in total Made of eNdoderm 1st Pouch Forms portions of inner ear Eustachian tube Middle ear cavity Contributes to tympanic membrane Pharyngeal Pouches 2nd Pouch 3rd Pouch Lining of palatine tonsils Ventral- Thymus Forms buds Dorsal- Inf Parathyroid Invaded by mesoderm glands (L and R on neck) Invaded by lymphatic tissue 4th Pouch Ventral Ultimobranchial body (c-cells) Incorporates into thyroid Forms C-cells (calcitonin) Derived from neural crest cells Dorsal Sup. Parathyroid glands Lecture quiz In the 4th week, the first brachial arch divides into? -Maxilla and mandible What cartilage does the 2nd Arch give rise to? -Reichert’s Does Treacher Collins cause cleft cyst? -NO Arytenoid DiGeorge Syndrome Thymic Aplasia Failure of 3rd/4th pharyngeal pouch to form Most cases: 22q11 chromosomal deletion Abnormal thymus, parathyroid function Classic triad: o Loss of thymus (Loss of T-cells, recurrent infections) o Loss of parathyroid glands (hypocalcemia, tetany) o Congenital heart defects (“conotruncal”) Pharyngeal Clefts 4 Clefts Lined by ectoderm 1st Cleft = external auditory meatus 2nd – 4th = cervical sinus o Temporary Cavity o Obliterates in development Branchial Cleft Cyst Present as neck mass o Location based on cleft of origin o 2nd cleft cysts are most common o Below angle of the mandible Anterior to sternocleidomastoid muscle Often noticed when becomes infected Fistula to skin may develop Often occurs in children Mass does not move with swallowing Contrast with thyroglossal duct cyst o Midline neck mass o Moves with swallowing Cleft Lip and Palate Cleft lip: Most common craniofacial malformation (1/1600) Cleft lip and palate often occur together Result from tissues of face not joining properly during development. Multifactorial etiology: o Environmental o Medication (antiseizure, methotrexate) o Vitamin deficiency o Obesity o Genetic Cleft Lip Lip forms btwn the 4th and 7th weeks of pregnancy o Openings in a baby's upper lip o Primary palate (front of palate) Due to failure of fusion of: o Intermaxillary segment (merged medial nasal processes) with maxillary process (formation of 1° palate) Ultrasound detected: 13th week of pregnancy Cleft Palate The roof of the mouth (palate) is formed btwn the 6th and 9th weeks of pregnancy Failure of fusion of the two lateral palatine shelves or failure of fusion of lateral palatine shelf with the nasal septum and/or 1° palate (formation of 2° palate) Openings in a baby's roof of the mouth (palate) Summary: Cleft lip and palate have distinct, multifactorial etiologies but often occur together Cleft lip o Openings in a baby's upper lip o Failure of fusion of intermaxillary segment (merged medial nasal processes) w the maxillary process (formation of 1° palate) speech issues, oral hygiene issues, feeding issues, lots of cavities Cleft palate o Openings in a baby's roof of the mouth (palate) o Caused by failure of fusion of the two lateral palatine shelves or failure of fusion of lateral palatine shelf with the nasal septum and/or 1° palate (formation of 2° palate)