Sentidos de inclusión-concesión (S6, S7, S8)

The process of swallowing is usually divided into three phases: oral (buccal), pharyngeal and esophageal. The swallowing center in medulla integrates functions of cranial nerves V, VII, IX, X and XII. Various mechanical and neuromuscular conditions can disrupt this process.

„ _{Oral phase: The food is chewed, lubricated and converted}

into a bolus, which is then propelled into the pharynx. The tongue is elevated against the palate and food is propelled into oropharynx. It is a voluntary phase.

„ _{Pharyngeal phase: Once the bolus of food comes into}

oropharynx, a series of reflex actions occurs, which do not allow the food to go into nasopharynx, oral cavity and larynx and facilitate carrying the food past oropharynx and laryngopharynx into the esophagus.

 Nasopharynx: Closure of nasopharynx, which occurs

when soft palate contracts against the Passavant’s ridge, cuts of the nasopharynx from oropharynx.

 _{Oropharynx: Closure of oropharyngeal isthmus, which}

occurs due to the sphincteric action of palatoglossal muscles when tongue contracts against palate, prevents the entry of food back into oral cavity.

 Larynx: Closure of laryngeal inlet by contraction of

aryepiglottic folds and closure of false and true cords prevent aspiration of food material into the larynx. There occurs temporary cessation of respiration and rising of larynx under the base of tongue. The function of epiglottis is not clear but is seen deflecting backwards while food passes into the pyriform fossa.

 _{Hypopharynx: When pharyngeal muscles contract}

cricopharyngeus muscles relax and food passes from pharynx into the esophagus. These actions are well timed and synchronous.

„ _{Esophageal phase: Once the food enters into the esophagus,}

cricopharyngeal sphincter closes and primary peristalsis of

abdominal pressure.

„ _{Pinch-cock effect of diaphragm.} „ _{Mucosal folds.}

„ _{Esophago-gastric angle.}

Heartburn (Pyrosis) refers to the feeling of substernal burning

and is highly specific of gastroesophageal reflux disease (GERD).

eMBRyOlOGy

Pharyngeal apparatus (Fig. 23)

It consists of pharyngeal arches (1, 2, 3, 4 and 6), internal pouches (1, 2, 3 and 4) and external grooves (1, 2, 3 and 4). Figure 23 and 24 summarize their anatomic associations in fetus and adults.

Pharyngeal arches (Fig. 24)

Table 2 summarizes the relationships among the nerves and adult structures derived from the pharyngeal arches and myotomes. First Arch Syndrome: it occurs from abnormal development of i pharyngeal arch. the faulty migration of neural crest cells causes facial anomalies. the two well-described syndromes are following:

1. treacher Collins Syndrome: it consists of mandibular and zygomatic hypoplasia and patients have down-slanted palpebral fissure, coloboma and malformed ear.

2. pierre Robin Sequence: it is a triad of poor mandibular growth, cleft palate and posteriorly placed tongue.

Fig. 23: Branchial apparatus showing branchial arches,

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Chapter 3

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a

natomy and Physiology of Oral Cavity

, Pharynx, and

e

sophagus

Fig. 24: Derivatives of branchial arches

taBle 2 the neural, muscular and skeletal elements derived from pharyngeal arches and myotomes; and skel- etal muscles innervated by cranial nerves

Arches and Myotomes Nerve Muscles Skeletal i arch mandibular division of

trigeminal nerve (Cn V3)

mastication (masseter, temporalis, medial and lateral pterygoids), mylohyoid, anterior belly of digastric and tensor tympani and palati

mandibular process-mandible, maxillary process-maxilla (meckel’s cartilage), malleus, incus and sphenomandibular ligament

ii arch Facial nerve (Cn Vii) muscles of facial expression, posterior belly of digastric, stylohyoid, stapedius

Hyoid (lesser horn and upper body), styloid process, stapes and stylohyoid ligament

iii arch Glossopharyngeal nerve (Cn iX)

Stylopharyngeus Hyoid (greater horn and lower body)

iV arch Vagus (Cn X): External laryngeal nerve branch of superior laryngeal nerve

Cricothyroid and inferior constrictor thyroid cartilage

Vagus (Cn X): pharyngeal branches to pharyngeal plexus

All the muscles of palate (except tensor palati) and pharynx (except stylopharyngeus and inferior constrictor)**

V arch Lost

Vi arch Vagus nerve (Cn X): Recurrent laryngeal nerve

All the intrinsic muscles of larynx (except cricothyroid) and inferior constrictor

Cricoid, arytenoid, corniculate, and cuneiform cartilages

myotome Accessory nerve (Cn Xi) trapezius and sternocleidomastoid Skull and scapula Occipital myotome Hypoglossal nerve (Cn X) All the muscles of tongue except

palatoglossus

preoptic myotome Oculomotor (Cn iii) All the extraocular muscles except lateral rectus and superior oblique trochlear (Cn iV) Superior oblique

Abducens (Cn Vi) Lateral rectus

** the development of pharyngeal and palatine muscles (innervated by vagus nerve) are controversial.

Pharyngeal Pouches and Grooves

Table 3 summarizes the adult structures derived from the pharyngeal pouches and grooves.

DiGeorge Sequence: it consists of involvement of neural crest cells and the failure of iii and iV pharyngeal pouches to differentiate into the parathyroids and thymus. the patient presents with following problems:

1. immunological problems. 2. Hypocalcemia.

3. Cardiovascular defects such as persistent truncus arteriosus. 4. Abnormal ears.

5. micrognathia.

• Ectopic parathyroid or thymus: they are generally found along the lateral aspect of neck and important during neck surgery. they result from abnormal migration of parathyroids and thymus from iii and iV pharyngeal pouches to their adult positions.

• Branchial Fistula: This pharyngeal fistula occurs when II pharyngeal pouch and groove persist. it is generally found along the anterior border of sternocleidomastoid muscle. • Branchial Cyst: this pharyngeal cyst forms when pharyngeal

grooves, which normally obliterates, persist. it is usually located in the upper neck near the angle of mandible.

thyroid Gland

Thyroid gland develops from midline thyroid diverticulum that forms in the floor of foregut and migrates caudally to its adult position. The thyroglossal duct, which is later obliter- ated, connects the thyroid diverticulum to the foregut that is indicated by foramen cecum in adults.

• Thyroglossal cyst or fistula: They occur in midline of neck when parts of thyroglossal duct persist. the cyst is generally seen near the hyoid bone but may also be found at the base of tongue (lingual cyst).

• Ectopic thyroid: Ectopic thyroid tissue may be found in the midline of neck along the course of thyroglossal duct.

Section 1

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Basic Sciences

tongue

„ _Mucosa:

– _{Anterior two-third of the tongue is associated with}

I pharyngeal arch and innervated by lingual branch of mandibular division of trigeminal nerve (CN V₃).

– _{Posterior one-third of tongue is associated with III}

pharyngeal arch and is innervated by glossopharyn- geal nerve (CN IX).

„ _{Muscles: Intrinsic and extrinsic muscles of tongue develop}

i Groove Epithelial lining of external auditory canal Rest of the

Grooves

Obliterated

** neural crest cells migrate into ultimobranchial body and form parafollicular cells of thyroid gland.

Palate

1. Intermaxillary segment and primary palate: The two medial nasal prominences fuse together at the midline and develop into the following structures that lie anterior to incisive foramen:

a. Philtrum of upper lip b. Four incisor teeth c. Primary palate

2. Secondary palate: It develops from two palatine shelves (outgrowths of maxillary prominences) that fuse together in midline posterior to incisive foramen.

Cleft palate: it occurs when two palatine shelves fail to fuse together in midline or the primary palate.

1. Philtrum: Vertical midline sulcus of upper lip extending from nasal columella to vermilion border. 2. Waldeyer’s ring: this ring of lymphoid tissue is situated in both nasopharynx and oropharynx.

3. adenoids: they are situated in the roof and posterior wall of nasopharynx and do not have a capsule on external surface. they do not have crypts. they are present at birth and usually disappear by puberty.

4. Second pharyngeal pouch: palatine tonsil develops in the second pharyngeal pouch. 5. Main blood supply to tonsil: it is from the tonsillar branch of facial artery.

6. Passavant’s ridge: it represents superior interdigitation of the superior constrictor and palatopharyngeal muscles. 7. Killian-Jamieson’s space: It lies between cricopharyngeus and circular fibers of the esophagus.

8. Killian dehiscence: it is found between thyropharyngeus and cricopharyngeus.

9. Structures passing between superior and middle constrictors: Glossopharyngeal nerve and stylopharyngeus muscle. 10. Structure passing between middle and inferior constrictor muscles: Superior laryngeal artery and vein and internal

laryngeal branch of superior laryngeal nerve.

11. Rouviere’s node: this most superior node of the lateral group of retropharyngeal lymph nodes is common site of lymphatic metastasis from the nasopharynx.

12. Structures passing between upper border of superior constrictor muscle and base of skull: they are levator veli palatini, Eustachian tube, and ascending palatine artery.

13. lamier hackemann’s space: it lies between circular and longitudinal fibers of the esophagus.