د. حسين جاسم
The pharynx

L.1   Anatomy & Physiology
   
   The pharynx is a fibromuscular tube situated in the upper part of the respiratory & digestive systems it extend from the base of the skull to the level of C6 cervical vertebra .In this extension its related to the nose superiorly & to the oral cavity in the middle & to the digestive system below where it becomes continuous with the esophagus at the level of the cricoid cartilage (C6 level).
   It’s a funnel shape covered by fascia attached to the base of the skull internally (the pharyngo-basilar fascia) & externally (bucco-pharyngeal fascia), it's divided into three parts: -
 
1. The nasopharynx:                                                                                                                
       It lies anterior to the first cervical vertebra (C1)&is limited superiorly by the base of the skull & inferiorly by the soft palate. The anterior wall lies opposite to the nose, the inferior wall lies opposite to oropharynx, the lateral wall has the opening of the Eustachian tubes & behind this opening there is an eminence called: Eustachian cushion & behind the Eustachian cushion there is depression (recess) called: fossa of Rosenmuller    which is covered by mucosa  & is the  commonest site of malignant tumers development in the nasopharynx.
         In the roof of the nasopharynx there is lymphoid tissue aggregation called: pharyngeal tonsil (adenoid) which is situated in the submucosa of the nasopharynx at the junction of the roof & the posterior wall of the nasopharynx. When these tonsils swollen it can cause closure of the nose anteriorly & closure of the Eustachian tube laterally.                                                                                                                         

2. The oropharynx:                                                                                     
               It lies against the (C2, C3) vertebrae & is the middle part of the pharynx which is related to the oral cavity anteriorly, to the soft palate superiorly, to the epiglottis inferiorly. The lateral walls contain the palatine tonsils, which are situated between 2-folds (pillars), the anterior one is formed by the palatoglossus muscle & the posterior one is formed by the palatopharyngeus muscle. The palatine tonsils form part of a complete ring of lymphoid tissue called: Waldeyers ring that surrounds the entry of the air & food passages.  
                 The mucosa of this lymphoid tissue has the ability to uptake the (Ag) which induces stimulation of the Ag-receptors (T & B lymphocytes) causing an inflammatory response & then production of (IgA, IgG & few amount of IgD) as adeffence mechanism to infection in this area. Repeated (recurrent) infection causing repeated Ag reaction which is sometimes so sever to produce lymphatic tissue hypertrophy (tonsils & adenoid) causing airway obstruction where surgical removal of the obstructing tissue take advance over immunity function. Sometimes the Ag-reaction may involve the mesenteric lymph nodes (causing lower abdominal pain) that’s why tonsillitis is one of the differential diagnosis of acute appendicitis (so its important to examine the tonsils in patient with lower abdominal pain).
            The tonsil is an EFFERENT lymphatic tissue (has NO AFFERENT lymphatic vessels) & is composed of mucosa, muscle fibers, lymphatic tissue & capsule (formed by the pharyngobasiller fascia). The medial 1/3 of the tonsil is covered by mucosa, while the lateral 2/3 is covered by capsule & embedded in the lateral wall of the oral cavity.
           The tonsil has a rich blood supply (as seen in the diagram) coming mainly from the facial artery (branch from  the external carotid) this branch & the major venous drainage   the  paratonsiller vein forming the major sites of post tonsillectomy bleeding.

3. The hypopharynx (laryngopharynx):
              It lies against (C3, C4, C5&C6) cervical vertebrae, it opens anteriorly into the larynx & is bounded above by the upper border of the epiglottis & below by the lower border of the cricoid cartilage.
              The hypopharynx contain 3-areas (the posterior pharyngeal wall, the pyriform fossa, the post cricoid area). The posterior pharyngeal wall is formed by the middle & inferior constrictor muscles of the pharynx & its covering mucosa & continues laterally to form the lateral wall of the pyriform fossa while the ary-epiglottic folds of the supraglottis form the medial wall. The mucosa covering the cricoid & arytenoid cartilages forming the post cricoid area.
             
              The epiglottis is connected to the posterior 1/3 of the tongue (tongue base) by three folds 1-median &2-lateral glosso-epiglottic folds, the median fold divide the depression between the 2-lateral folds into 2-depressions called: the valleculae. The pharyngeal mucosa has a rich lymphatic supply, which can cause easy spread of tumer cells between different areas in the pharynx.   

Mechanism of swallowing:
    The act of swallowing is composed of three stages: the oral, pharyngeal & esophageal stage. This mechanism depend on an intact neurological muscular systems that control this mechanism in 2-phases (voluntary&involuntary).
     The neurological pathway include afferent nerve fibers ----medulla----efferent stimuli by the glossopharyngeal & vagus nerves, damage at any level of this pathway or damage to the muscles acting on swallowing will lead to dysphagia & regurgitation of fluid & food to the larynx & trachea leading to aspiration pneumonia.
       The voluntary phase started at the mouth (chewing) which require intact teeth & tongue & then the bollus of food is pushed to the pharynx voluntarily where the involuntary phase begins (in this time the soft palate is elevated to close the nasopharynx & prevent regurgitation of food to the nose). Then the sensory part of the mandibular branch of the trigeminal nerve send impulses to the brain stem then through the glossopharyngeal & vagus nerves impulses reach the (superior, middle, inferior) constrictors of the pharynx causing contraction & pushing of food to the upper esophageal sphincter which opens to the esophageal lumen where a peristaltic wave started pushing the food to the lower esophageal sphincter.

Pharyngeal Spaces:
1.	Retropharyngeal space :
       Which is aspace between the vertebral column & the posterior wall of the pharynx, it’s covered anteriorly by the buccopharyngeal fascia its apotential space containing the retropharyngeal lymph nodes, which may be inflamed specially in children causing expansion of the space anteriorly & airway obstruction & dysphagia which need urgent surgical drainage.
2.	Parapharyngeal space:
        It lies on each side of the pharynx deep to the sternomastoid muscle extending from the skull base to the superior mediastinum, also its apotential space containing (the carotid artery, internal jugular vein, sympathetic trunk, four cranial nerves & the deep cervical lymph nodes) the lymph nodes may be enlarged in inflammation of the lower 3rd molar tooth & in tonsillitis leading to abscess formation pushing the lateral wall of the pharynx medially.