Pharynx

 Introduction 

The pharynx is a wide muscular tube,
situated behind the nose, the mouth and the larynx.
Clinically, it is a part of the upper respiratory passages where infections are common.
The upper part of the pharynx transmits only air, the lower part (below the inlet of the larynx), only food, but the middle part is a common passage for both air and food 

Dimensions of Pharynx 

Length: About 12 cm.
width:
1. Upper part is widest (3.5 cm) and noncollapsible
2. Middle part is narrow
3. The lower end is the narrowest part of the gastrointestinal tract (except for the appendix). 

Boundaries 

Superiorly 

Base of the skull, including the posterior part of the body of the sphenoid and the basilar part of the occipital bone, in front of the pharyngeal tubercle.
Inferiorly 

The pharynx is continuous with oesophagus at the level of C6 vertebra, corresponding to the lowest border of cricoid cartilage 

Posteriorly
The pharynx glides freely on the prevertebral fascia which separates it from the cervical vertebral bodies 

Anteriorly 

It communicates with the nasal cavity, the oral cavity and the larynx. Thus the anterior wall of the pharynx is incomplete
On each side
1. The pharynx is attached to: 

a. Medial pterygoid plate
b. Pterygomandibular raphe
c. Mandible
d. Tongue
e. Hyoid bone
f. Thyroid and cricoid cartilages.
2. It communicates on each side with the middle ear cavity through the auditory tube.
3. The pharynx is related on either side to:
a. The styloid process and muscles attached to it
b. The common carotid, internal carotid & external carotid arteries and cranial nerves related to them. 

Parts of the Pharynx 

The cavity of the pharynx is divided into: 

1. Nasal part, Nasopharynx
2. Oral part, Oropharynx
3. Laryngeal part, Laryngopharynx 

Nasopharynx 

Situation - Behind nose
Extent - Base of skull (body of sphenoid) to soft palate
Communications - Anteriorly with nose 

Nerve supply - Pharyngeal branches of pterygopalatine ganglion
Relations: 

i. Anterior - Posterior nasal aperture
ii. Posterior and roof - Body of sphenoid bone and basiocciput and anterior arch of atlas.
Presence of a. Nasopharyngeal tonsil prominent in children
b. Nasopharyngeal bursa - mucus diverticulum
iii. Lateral wall - Opening of auditory tube above this is tubal elevation with tubal tonsil 

Lining epithelium - Ciliated columnar epithelium
Function - Passage for air (respiratory function) 

Oropharynx 

Situation - Behind oral cavity
Extent - Soft palate to upper border of epiglottis
Communication -
1. Anteriorly with oral cavity,
2. Above with nasopharynx
3. Below with laryngopharynx
Nerve supply - lX and X nerves 

Relations: 

Anterior - Oral cavity
Posterior and roof - Body of second and third cervical vertebrae
Lateral wall - Tonsillar fossa containing palatine tonsil 

Lining epithelium - Stratified squamous nonkeratinised epithelium
Function - Passage for air and food 

Laryngopharynx 

Situation - Behind larynx.
Extent - Upper border of epiglottis to lower border of cricoid cartilage
Communication - 

lnferiorly with oesophagus 

Anteriorly with larynx 

Above with oropharynx 

Nerve supply - lX and X nerves 

Relations: 

Anterior - 

1. lnlet of larynx,
2. Posterior surface of cricoid cartilage 

3. Arytenoid cartilage 

Posterior and roof - 

Fourth and fifth cervical vertebrae
Lateral wall - Piriform fossa on each side of inlet of larynx, bounded by aryepiglottic fold medially and thyroid cartilage laterally.
Lining epithelium - Stratified squamous nonkeratinised epithelium
Function - Passage for food 

Structure of Pharynx 

The wall of the pharynx is composed of the following five layers from within outwards.
1. Mucosa
2. Submucosa 

3. Pharyngobasilar fascia or pharyngeal aponeurosis. 

This is a fibrous sheet internal to the pharyngeal muscles.
It is thickest in the upper part where it fills the gap between the upper border of the superior constrictor and the base of the skull, and also posteriorly where it forms pharyngeal raphe. Superiorly, the fascia is attached to basiocciput, the petrous temporal bone, the auditory tube, posterior border of the medial pterygoid plate, and pterygomandibular raphe.

Inferiorly, it is gradually lost deep to muscles, and hardly extend beyond the superior constrictor. 

4. The muscular coat consists of 

an outer circular layer 

made up of the three constrictors (superior, middle and inferior) and 

an inner longitudinal layer 

made up of the stylopharyngeus, the salpingopharyngeus and the palatopharlmgeus muscles..

5. The buccopharyngeal fascia covers the outer surface of the constrictors of the pharynx and extends forwards across the pterygomandibular raphe to cover the buccinator.

Like the pharyngobasilar fascia, the buccopharyngeal fascia is best developed in the upper part of the pharynx. 

Between the buccopharyngeal fascia, and the muscular coat there are the pharyngeal plexuses of veins and nerves 

Muscles of the Pharynx - General features 

The muscular basis of the wall of the pharynx is formed mainly by
the three pairs of constrictors - superior, middle and inferior. 

The origins of the constrictors are situated anteriorly in relation to the posterior openings of the nose, the mouth and the larynx.
From here their fibres pass into the lateral and posterior walls of the pharynx, the fibres of the two sides meeting in the mid line in a fibrous raphe. 

The three constrictors are so arranged that the inferior overlaps middle which in turn overlaps the superior. 

The fibres of the superior constrictor reach the base of the skull posteriorly, in the middle line.
On the sides, however, there is a gap between the base of the skull and the upper edge of the superior constrictor. 

This gap is closed by the pharyngobasilar fascia which is thickened in this situation. 

The lower edge of the inferior constrictor becomes continuous with the circular muscle of the oesophagus. These muscles develop from IV and VI pharyngeal arch 

The superior constrictor takes origin from the 

following (from above downwards): 

• Pterygoid hamulus (pterygopharyngeus).
• Pterygomandibular raphe (buccopharyngeus).
• Medial surface of the mandible at the posterior end of the mylohyoid line, i.e. near the lower attachment of the pterygomandibular raphe (mylopharyngeus).
• Side of posterior part of tongue (glossopharyngeus). 

The middle constrictor takes origin from: 

The lower part of the stylohyoid ligament
Lesser cornua of hyoid bone
Upper border of the greater cornua of the hyoid bone. 

The inferior constrictor consists of two parts. 

The thyropharyngeus arises from:
a. The oblique line on the lamina of thyroid cartilage, including the inferior tubercle.
b. A tendinous band that crosses the cricothyroid muscle and is attached above to the inferior tubercle of the thyroid cartilage.
c. The inferior cornua of the thyroid cartilage. 

The cricopharyngeus arises from the cricoid cartilage behind the origin of the cricothyroid muscle. 

lnsertion of Constrictors 

All the constrictors of the pharynx are inserted into a median raphe on the posterior wall of the pharynx.
The upper end of the raphe reaches the base of the skull where it is attached to the pharyngeal tubercle on the basilar part of the occipital bone 

Longitudinal Muscle Coat 

The pharynx has three muscles that run longitudinally.
1. The stylopharyngeus arises from the styloid process. 

It passes through the gap between the superior and middle constrictors to run downwards on the inner surface of the middle and inferior constrictors. 

2. The fibres of the palatopharyngeus descend from the sides of the palate and run longitudinally on the inner aspect of the constrictors 

3. The salpingopharyngeus descends from the auditory tube to merge with palatopharyngeus 

Structures passing in between the pharyngeal muscles
Features
1. The large gap between the upper concave border of the superior constrictor and the base of the skull is semilunar and is known as the sinus of Morgagni. 

It is closed by the upper strong part of the pharyngobasilar fascia
The structures passing through this gap are:
a. The auditory tube. 

b. The levator veli palatini muscle.
c. The ascending palatine artery
d. Palatine branch of ascending pharyngeal artery.
2 .The structures passing through the gap between the superior and middle constrictors are:
The stylopharyngeus muscle and the glossopharyngeal nerve.
3. The internal laryngeal nerve and the superior
laryngeal vessels pierce the thyrohyoid membrane
in the gap between the middle and inferior constrictors.
4. The recurrent laryngeal nerve and the inferior laryngeal vessels pass through the gap between the lower border of the inferior constrictor and the oesophagus 

Killian's Dehiscence 

In the posterior wall of the pharynx, the lower part of the thyropharyngeus is a single sheet of muscle,
not overlapped internally by the superior and middle constrictors. 

This weak part lies below the level of the vocal folds or upper border of the cricoid lamina and
is limited inferiorly by the thick cricopharyngeal sphincter. 

This area is known as Killian's dehiscence. Pharyngeal diverticula are formed by out pouching of the dehiscence
Such diverticula are normal in the pig.
Pharyngeal diverticula are often attributed to neuromuscular incoordination in this region which may be due to the fact that different nerves supply the 

two parts of the inferior constrictor. 

The propulsive thyropharyngeus is supplied by the pharyngeal plexus, and
sphincteric cricopharyngeus, by the recurrent larlngeal nerve. 

If the cricopharyngeus fails to relax when the thyropharyngeus contracts, the bolus of food is pushed backwards, and tends to produce a diverticulum. 

Nerve Supply 

The pharynx is supplied by the pharyngeal plexus of nerves which lies chiefly on the middle constrictor.
The plexus is formed by:
1. The pharyngeal branch of the vagus carrying fibres of the cranial accessory nerve. 

2. The pharyngeal branches of the glossopharyngeal nerve. 

3. The pharyngeal branches of the superior cervical sympathetic ganglion.
• Motor fibres are derived from the cranial accessory nerve through the branches of the vagus. 

• They supply all muscles of pharynx, except the stylopharyngeus which is supplied by the glossopharyngeal nerve.
• The inferior constrictor receives an additional supply from the external and recurrent laryngeal nerves. 

• Sensory fibres or general visceral afferent from the pharynx travel mostly through the glossopharyngeal nerve, and partly through the vagus.
  
• the nasopharynx is supplied by the maxillary nerve through the pterygopalatine ganglion; and
  
• the soft palate and tonsil, by the lesser palatine and glossopharyngeal nerves.
  
• Taste sensations from the vallecula and epiglottic area pass
  through the internal laryngeal branch of the vagus.
  
• The parasympathetic secretomotor fibres to the pharynx are
  derived from the lesser palatine branches of the pterygopalatine ganglion 

BIood Supply 

The arteries supplying the pharynx are as follows.
1. Ascending pharyngeal branch of the external carotid artery.
2. Ascending palatine and tonsillar branches of the facial artery.
3. Dorsal lingual branches of the lingual artery.
4. The greater palatine, pharyngeal and pterygoid branches of the maxillary artery. 

The veins form a plexus on the posterolateral aspect of the pharynx.
The plexus receives blood from the pharynx, the soft palate and the prevertebral region. It drains into the internal jugular and facial veins. 

Lymphatic Drainage 

Lymph from the pharynx drains into the retropharyngeal and deep cervical lymph nodes. 

Deglutition (Swallowing) 

Swallowing of food occurs in three stages described below. 

First Stage 

1. This stage is voluntary in character.
   
2. The anterior part of the tongue is raised and pressed against the hard palate by the intrinsic muscles of the tongue, especially the superior longitudinal and transverse muscles. The movement takes place from anterior to the posterior side. This pushes the food bolus into the posterior part of the oral cavity. 
3. The soft palate closes down on to the back of the tongue, and helps to form the bolus.
   
4. Next, the hyoid bone is moved upwards and forwards by the suprahyoid muscles.
   The posterior part of the tongue is elevated upwards and backwards by the styloglossi muscles and the palatoglossal arches are approximated by the palatoglossi muscles.
   This pushes the bolus through the oropharyngeal isthmus to the oropharynx, and the second stage begins.
   

Second Stage 

1. It is involuntary in character. 

During this stage, the food is pushed from the oropharynx to the lower part of the laryngopharynx. 

2. The nasopharyngeal isthmus is closed by elevation of the soft palate by levator veli palatini and tensor
veli palatini and by approximation to it of the posterior pharyngeal wall (ridge of Passavant). 

This prevents the food bolus from entering the nose.
3. The inlet of larynx is closed by approximation of the aryepiglottic folds by aryepiglottic and oblique arytenoid muscles. 

This prevents the food bolus from entering the larynx.
4. Next, the larynx and pharynx are elevated behind the hyoid bone by the longitudinal muscles of the pharynx, and the bolus is pushed down over the posterior surface of the epiglottis, the closed inlet of the larynx and the posterior surface of the arytenoid cartilages, by gravity, and by contraction of the superior and middle constrictors and of the palatopharyngeus. 

Third Stage 

1. This is also involuntary in character. 

In this stage, food passes from the lower part of the pharynx to the oesophagus. 2. This is brought about by the inferior constrictors of the pharynx.
Clinical Anatomy 

Difficulty in swallowing is known as dysphagia 

DEVELOPMENT 

The primitive gut extends from the buccopharyngeal membrane cranially, to the cloacal membrane caudally.
It is divided into four parts - the pharynx, the foregut, the midgut and the hindgut.
The pharynx extends from buccopharyngeal membrane to the tracheobronchial diverticulum. 

It is divided into upper part, the nasopharynx; middle part, the oropharynx; and the lower part, the laryngopharynx.

Watch lectures on YouTube:

Pharynx | Extent | Relations | Parts | Boundaries | Features

Structure of Pharynx | Layers | Muscles - Constrictors & Longitudinal | Nerve Supply |Deglutition |