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The pharynxL.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. Theanterior 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 ofthe 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.