PHARYNGEAL (BRANCHIAL) ARCHES• Derived from neural crest cells• Resemble fish gills (branchia)• Begin to develop early in the 4th week• By end of 4th week, four pairs of arches are visible on the surface (not 5th and 6th ) and a buccopharyngeal membrane ruptures forming communication between primitive oral cavity and foregut
PHARYNGEAL ARCHES (CONT.)• Contribute to the formation of the neck as well as the face.• Visible structures at 42 weeks: 1st arch: mandibular prominence, maxillary prominences, and the frontonasal prominence
PHARYNGEAL ARCHES (CONT.)• Core of mesenchymal tissue covered by surface ectoderm (outside) and by endodermal epithelium (inside)• Ectoderm -> skeletal• Mesoderm -> muscles with accompanying nerve• Arterial component (aortic arches)• Therefore, each arch carries nerve, muscle, bone and blood supply
FIRST PHARYNGEAL ARCH• Maxillary process (dorsal) – Premaxilla, maxilla, zygomatic bone, portion of temporal bone• Mandibular process (ventral) – Contains Meckel’s cartilage which disappears except for dorsal end (incus & malleus) and mandible
FIRST PHARYNGEAL ARCH• Muscles of mastication, digastric (ant belly), mylohyoid, tensor tympani and tensor palatini• Therefore, the accompanying motor nerve is the mandibular branch of trigeminal (V2) and sensory are V1, V2, and V3• 1st aortic arch practically disappears but forms the maxillary artery
SECOND PHARYNGEAL ARCH• Reichert’s cartilage – stapes, styloid process, stylohyoid ligament, lesser horn and upper part of the hyoid• Muscles include: stapedius, stylohyoid, digastric (post belly), auricular, and those of facial expression• Facial nerve (CN VII)• 2nd aortic arch – stapedial & hyoid arteries
THIRD PHARYNGEAL ARCH• Cartilaginous contributions include greater horn and lower part of hyoid• Sole muscle: stylopharyngeus• CN IX (Glossopharyngeal nerve)• 3rd aortic arch (quite large): common carotid, 1st portion of internal carotid (remainder dorsal aorta), and external carotid
FOURTH & SIXTH PHARYNGEAL ARCH• Cartilaginous contributions to larynx derived from fusion: thyroid, cricoid, arytenoid, corniculate, and cuneiform• Muscles of 4th: cricothyroid, levator palatini, and pharyngeal constrictors are innervated by SLN (CN X)• Muscles of 6th: intrinsics of larynx are innervated by RLN (CN X)• 4th aortic arch: L->arch of aorta & R->subclavian• 6th aortic arch: L & R pulmonary with ductus arteriosus on left
ANATOMY (CONT…)• It is a conical fibromuscular tube forming upper part of air and food passage. It is 12-14 cm long. Extends from base of skull to inferior border of cricoid cartilage anteriorly and inferior border of C6 posteriorly• Widest portion (5cm) at hyoid• Narrowest portion (1.5cm) at caudal end• Divided into 3 parts: nasopharynx, oropharynx, and laryngo(hypo)pharynx
NASOPHARYNX/EPIPHARYNX• Anterior: choana (posterior nasal aperture)• Posterior: pharyngobasilar membrane, superior constrictor muscle, arch of atlas covered by prevertebral muscle and fascia.• Superior: basi-occiput and basi-sphenoid.• Inferior: soft palate (Anteriorly) deficient posteriorly-nasopharyngeal isthmus.• Lateral :pharyngeal opening of eustachian tube situated 1.25 cm behind the posterior end of inferior turbinate, bounded by torus tubaris. above and behind the tubal elevation is a recess- fossa of Rosenmuller.
STRUCTURES OF PHARYNGEAL WALL1. Mucus membrane-ciliated columnar in nasopharyx and stratified squamous in other areas.2. Pharyngeal aponeurosis ( pharyngo-basilar fascia)3. Muscular coat-external layer contains superior , middle, inferior constrictors. Internal layer-stylopharyngeus, salpingopharyngeus, palatoparyngeus.4. Buccopharyngeal fascia.
KILLIAN’S DEHISCENCE• Inferior constrictor muscle has two parts -thyropharyngeus with oblique fibres and cricopharyngeus with transverse fibres. A potential gap between these two parts is called killian’s dehiscence. Also called “gateway of tears” as perforation can occur during esophagoscopy. This is also the site of mucosal herniation in case of pharyngeal pouch.
NASOPHARYNGEAL TONSIL• Tonsil - It is a sub epithelial collection of lymphoid tissue at the junction of roof and posterior wall of nasopharynx. it increases in size up to 6 yrs and then gradually atrophies.• Bursa - epithelial lined median recess found within the adenoid mass and extends from pharyngeal mucosa to periosteum of basiocciput. It represents attachment of notochord to the pharyngeal endoderm during embryonic life. Sometimes an abscess can form in the bursa -Thornwald’s disease.
TUBAL TONSIL AND SINUS OF MORGAGNI• Tubal tonsil-Collection of subepithelial lymphoid tissue situated at the tubal elevation. It is continuous with nasopharyngeal tonsil forms a part of waldeyar’s ring.• Sinus of Morgagni - space between the base of the skull and free upper border of superior constrictor muscle. Eustachian tube, levator veli palatine, tensor veli palatine and ascending pharyngeal artery passes through it.
PASSAVANT’S RIDGE• It is a mucosal ridge raised by fibres of palato-pharyngeus. It encircles the posterior and lateral walls of nasopharyngeal isthmus. Soft palate during contraction, makes firm contact with this ridge to cut off nasopharynx from the oropharynx during deglutition or speech.
WALDEYER’S RING• Scattered subepithelial lymphoid aggregates in and around pharynx are collectively called waldeyer’s ring• It consists of inner ring and outer ring• Inner ring: nasopharyngeal tonsil, palatine tonsil, lingual tonsil, tubal tonsil, lateral pharyngeal bands, nodules in posterior pharyngeal wall• Outer ring: lymph nodes at retropharyngeal, styloid, lateral pharyngeal, behind sternomastoid, at bifurcation of common carotid, in front of sternomastoid, at angle of jaw, at hyoid and subhyoid
FUNCTIONS OFNASOPHARYNX1. Conduit for air.2. Ventilation of middle ear and equalize pressure.3. With passavant’s ridge to cut off nasopharynx from oropharynx.4. Resonating chamber during voice production.5. Drainage channel for secretion drainage from nose.
OROPHARYNX• Extends from plane of hard palate above to plane of hyoid bone below.• Anterior: oropharynx communicates with oral cavity,• Posterior: related to retropharyngeal space opposite C2-3, superior constrictor through oropharyngeal isthmus.• Superior: soft palate• Inferior: base of tongue, lingual tonsils, valleculae, superior epiglottis.• Laterally: palatoglossal (Anteriorly) and palatopharyngeal arches (posteriorly), palatine (faucial) tonsil
FUNCTIONS OF OROPHARYNX1. Conduit for passage of food and air.2. Pharyngeal phase of deglutition.3. Vocal tract for certain speech sounds.4. Appreciation of taste.5. Local defense and immunity.
HYPOPHARYNX• Lowest part of larynx, Lies posterior and partly on sides of the larynx. lies opposite C3-6• Superior: superior border of epiglottis and pharyngoepiglottic folds (plane passing through body of hyoid bone)• Inferior: inferior border of the cricoid• Posterior/lateral: middle & inferior constrictors, bodies of C3-C6• Anterior: laryngeal inlet• Subdivided into three regions-pyriform sinus (fossa), post cricoid region, posterior pharyngeal wall.
PYRIFORM SINUS• Lies on either side of larynx and extends from pharyngoepiglottic fold to the upper end of esophagus.• boundaries: -laterally: thyrohyoid membrane and thyroid cartilage. -medially: aryepiglottic fold, posterolateral surface of arytenoid, cricoid cartilage.• Internal laryngeal nerve passes submucosally in lateral wall of sinus so easily accessible for local anaesthesia. In carcinoma of pyriform sinus this nerve causes referred otalgia.
PHARYNGEAL MUSCLES AND NERVE SUPPLY.• External circular and internal longitudinal (opposite in remainder of GI tract)• External: 3 constrictors (CN XI via X and ELN/RLN for middle and inferior) function to constrict wall of pharynx during swallow• Internal: palatopharyngeus and salpingopharyngeus (CN XI via X) and stylopharyngeus (CN IX) act to elevate pharynx and larynx during speech/swallow• CN V supplies nasopharynx
PHARYNGEAL MUSCLES(CONT…)• Tensor veli palatini (V3) tenses soft palate & opens ET during yawn/swallow• Levator veli palatini (CN XI via X) elevates palate during swallow/yawn• Palatoglossus (CN XI via X) approximates tongue and soft palate
BLOOD SUPPLY• Blood supply is by branches of external carotid artery1. Ascending pharyngeal. A2. Ascending palatine branch of facial. A3. Lingual. A4. Superior thyroid. A
VENOUS DRAINAGE• The veins form the pharyngeal plexus which drains into common facial vein and internal jugular vein
PARAPHARYNGEAL SPACE• Pyramidal in shape with its base at the base of skull and apex at the hyoid bone• Boundaries:a) Superior: base of skullb) Inferior: mediastinumc) Medial: buccopharyngeal fascia, prevertebral muscle and fasciad) Lateral: ramus of mandible, deep surface of parotid, medial pterygoid muscle• Contents: carotid artery, jugular vein, CN ix, x, xi, xii, cervical sympathetic trunk, deep cervical lymph nodes
RETROPHARYNGEAL SPACE (GILLETTE’S SPACE)• Space lies behind the pharynx, divided by a median partition into right and left compartment• Boundaries:a) Anteriorly: buccopharyngeal fasciab) Posteriorly: prevertebral fasciac) Superior extent: base of skulld) Inferior: bifurcation of trachea• Contents: retropharyngeal lymph nodes which usually disappear at 3-4 years of age.