The Pharynx

 The Pharynx    

The pharynx is situated behind the nasal cavities, the mouth, and the larynx and may be divided into nasal, oral, and laryngeal parts. The pharynx is funnel shaped, its upper, wider end lying under the skull and its lower, narrow end becoming continuous with the esophagus opposite the 6th cervical vertebra. The pharynx has a musculomembranous wall, which is deficient anteriorly. Here, it is replaced by the posterior openings into the nose, choanae the opening into the mouth, and the inlet of the larynx. By means of the auditory tube, the mucous membrane is also continuous with that of the tympanic cavity.

Muscles of the Pharynx

The muscles in the wall of the pharynx consist of three constrictor muscles-

·        Superior Constrictor

·        Middle Constrictor

·        Inferior Constrictor

Their fibers run in a somewhat circular direction

Following muscles are also found-

·        Stylopharyngeus

·        Salpingopharyngeus 

Their fibers run in a somewhat longitudinal direction.

The three constrictor muscles extend around the pharyngeal wall to be inserted into a fibrous band or raphe that extends from the pharyngeal tubercle on the basilar part of the occipital bone of the skull down to the esophagus.

The three constrictor muscles overlap each other so that the middle constrictor lies on the outside of the lower part of the superior constrictor and the inferior constrictor lies outside the lower part of the middle constrictor.

The lower part of the inferior constrictor, which arises from the cricoid cartilage, is called the cricopharyngeus muscle. The fibers of the cricopharyngeus pass horizontally around the lowest and narrowest part of the pharynx and act as a sphincter.

Killian’s dehiscence is the area on the posterior pharyngeal wall between the upper propulsive part of the inferior constrictor and the lower sphincteric part, the cricopharyngeus.

Structure of the Pharynx

The pharynx is divided into three parts:

·        nasal pharynx

·        oral pharynx

·        laryngeal pharynx

Nasal Pharynx

This lies above the soft palate and behind the nasal cavities. In the submucosa of the roof is a collection of lymphoid tissue called the pharyngeal tonsil. The pharyngeal isthmus is the opening in the floor between the soft palate and the posterior pharyngeal wall. On the lateral wall is the opening of the auditory tube, the elevated ridge of which is called the tubal elevation. The pharyngeal recess is a depression in the pharyngeal wall behind the tubal elevation. The salpingopharyngeal fold is a vertical fold of mucous membrane that covers the Salpingopharyngeus muscle.

Oral Pharynx

This lies behind the oral cavity. The floor is formed by the posterior one third of the tongue and the interval between the tongue and epiglottis. In the midline is the median glossoepiglottic fold, and on each side the lateral glossoepiglottic fold. The depression on each side of the median glossoepiglottic fold is called the vallecula. On the lateral wall on each side are the palatoglossal and the palatopharyngeal arches or folds and the palatine tonsils between them.

The palatoglossal arch is a fold of mucous membrane covering the palatoglossus muscle. The interval between the two palatoglossal arches is called the oropharyngeal isthmus and marks the boundary between the mouth and pharynx. The palatopharyngeal arch is a fold of mucous membrane covering the palatopharyngeus muscle. The recess between the palatoglossal and palatopharyngeal arches is occupied by the palatine tonsil.

 Laryngeal Pharynx

This lies behind the opening into the larynx. The lateral wall is formed by the thyroid cartilage and the thyrohyoid membrane. The piriform fossa is a depression in the mucous membrane on each side of the laryngeal inlet.

Sensory Nerve Supply

Nasal pharynx-The maxillary nerve (V2)

Oral pharynx- The Glossopharyngeal nerve

Laryngeal pharynx The internal laryngeal branch of the vagus nerve

Blood Supply of the Pharynx-Ascending pharyngeal, tonsillar branches of facial arteries, and branches of maxillary and lingual arteries.