Session 11: Pharynx Flashcards
Self-Study Thyroid Notes
The thyroid gland straddles the larynx and the trachea. It lies deep to the strap muscles (that constitute the infrahyoid muscles). The parathyroid glands (4 in number) are located on the posterior aspect of the thyroid gland.
Disorders and diseases of the thyroid and the parathyroids often require surgical exposure and excision of diseased glandular tissues. In thyroidectomy, accidental removal of the parathyroid tissue may result in disturbances in calcium and phosphorus metabolism.
Because of the profuse blood supply to endocrine glands, the knowledge of their important supply vessels is essential as these vessels are vulnerable to injury during surgical interventions. An enlarged thyroid gland may compress the recurrent laryngeal nerve affecting the movements of the vocal cords resulting in voice disorder.
The isthmus of the thyroid gland may have to be incised to expose the trachea during tracheostomy to keep the airway patent.
Describe the Pharynx
The Pharynx is the superior, expanded part of the Alimentary System, posterior to the nasal and oral cavities and extending inferiorly past the larynx. It is a muscular tube into which the nasal, oral and laryngeal cavities open.
The Pharynx extends from the Cranial Base to the Inferior Border of the Cricoid Cartilage Anteriorly and the Inferior Border of C6 Vertebra Posteriorly.
It is widest (Approximately 5cm) opposite the hyoid and narrowest (approximately 1.5cm) at its inferior end, where it is continuous with the oesophagus.
The posterior wall of the pharynx lies against the prevertebral layer of the deep cervical fascia.
Describe the Nasopharynx
- C1 Level
- Attached to the posterior skull and bounded anteriorly by the posterior nares.
- Boundaries:
- Superior: skull base
- Inferior: level of soft palate
- Anterior: posterior choanae (posterior nasal apertures)
- Posterior: nasopharyngeal tonsil, C1
- Respiratory Function as it is the posterior extension of the nasal cavities – through two choane.
- Continuous below with the oropharynx at the level of the soft palate.
- The auditory (Eustachian) tube opens into the nasopharynx. The opening of this orifice is controlled by a muscle that lies beneath the fold of mucous membrane of the region.
- Pseudostratified Ciliated Epithelium with Goblet Cells
- Lymphoid tissue forms a Tonsillar ring around the superior part of the pharynx, which aggregates to form the Adenoids. They lie in the mucous membrane of the roof and the posterior wall of the nasopharynx.The adenoids may become swollen during infection in children, blocking the Eustachian tube and leading to otitis media.
Describe the boudnaries, function and epithelium of the Oropharynx
Behind oral cavity and tongue
Boundaries
- Superior: level of soft palate
- Inferior: superior edge of glottis
- Anterior: oral cavity
- Posterior: C2-C3
Extends from the soft plate to the superior border of the epiglottis, where it is continuous with the larynopharynx which lies behind the laryngeal inlet, the arytenoids cartilage and the cricoids lamina.
Digestive Function
Stratified Squamous Epithelium non-Keratinised
Describe the Palatine Tonsils in the Oropharynx including blood supply, venous and lymph drainage.
- The palatine tonsils lie in tonsillar fossae on either side of the oropharynx in the interval between the palatoglossal (anterior pillar) and palatopharyngeal (posterior pillar) arches.
- The Palatoglossal arch’s boundary is between buccal cavity and oropharynx, fuses with lateral wall of tongue and contains palatoglossal muscle.
- The palatopharyngeal arch blends with wall of pharynx and contains the palatopharyngeus muscle.
- The palatine tonsils are tonsil encapsulated lymphoid tissue covered with squamous epithelium and crypts, part of the Waldeyer’s ring, atrophies after puberty. The tonsillar fossa floor is the superior constrictor muscle. The palatine tonsils are MALT.
- The blood supply to the palatine tonsils:
- Tonsillar branch of facial artery (also lingual/ascending palatineascending pharyngeal)
- Venous drainage pharyngeal plexus (also paratonsillar vein)
- Lymph drainage of the palatine tonsils:
- Lymphatics pierce superior constrictor muscle
- Pass to nodes along internal jugular vein
- Jugulodigastric node (angle of mandible)
Describe the Laryngopharynx (Hypopharynx)
- Posterior to the Larynx
Boundaries:
- Superior: superior edge of epiglottis
- Inferior: level of inferior edge of cricoid cartilage
- Anterior: larynx
- Posterior: C3-C6 Vertebrae
- Inferiorly opens into oesophagus (post) and larynx (ant) (leaf-shaped)
It lies behind the laryngeal inlet. On each side of the inlet, the laryngopharyngeal cavity has a small depression called the piriform fossae.
Stratified Squamous Epithelium non-keratinised
Fibrocartilage allows to move back and forth.
What is meant by Waldeyer’s Ring?
The pharynx has an incomplete ring of lymphoid tissue consisting of 3 named tonsils lying between the mucosa and muscles. The palatine tonsils lie between the palatoglossal and palatopharyngeal ridges. The pharyngeal tonsils (or adenoids) lie near the roof of the nasopharynx close to the point of entry of the auditory tubes whilst the lingual tonsils are situated beneath the mucosa of the posterior third of the tongue.
What are the 2 muscular components of the Pharynx?
The posterior and lateral walls of the pharynx are all formed by constrictor muscles. The wall of the Pharynx consists of an incomplete outer circular muscle layer and an inner longitudinal muscle layer. The muscle layer is covered internally by the Pharyngobasilar Fascia, which is in turn covered by the Mucous Membrane.
Describe the Outer Circular Muscle Layer
- Superior Constrictor
- Middle Constrictor
- Inferior Constrictor
- Lower horizontal fibres known as Cricopharyngeus
The outer muscles all attach posteriorly at the midline/median raphe. The muscles overlap each other and are incomplete anteriorly. During swallowing the muscle constrict sequentially from above to below to propel the bolus of food downwards (involuntarily during the swallowing reflex).
Describe the Inner Longitudinal Muscle Layer
- Stylopharyngeus
- Palatopharyngeus
- Salpingopharyngeus (in addition to swallowin, it also opens the Eustachian tube to equalize the pressure in the middle ear with the atmosphere).
During swallowing these muscles act to shorten and widen the pharynx and elevate the larynx during swallowing and speaking.
Describe what is meant by a Killian’s dehiscence and Pharyngeal Pouch
Between the two bellies (thyropharyngeal and cricopharyngeus) of the inferior constrictor (sometimes known as between the inferior constrictor and cricopharyngeus) is a small gap known as Killian’s dehiscence where mucosa of the pharynx can be sometimes trapped, thereby increasing the possibility of formation of a true diverticulum (of Zenker), also known as a pharyngeal pouch (just proximal).
Thus, as food is conveyed through the pharynx, some of it may be trapped in the pouch. Some pouches can be asymptomatic (i.e. small) but others can give rise to dysphagia, regurgitation of food or even halitosis.
Pharyngeal Pouch: posterior herniation of pharyngeal mucosa.
This can be due to the fact that it is a weaker area, incoordination of pharyngeal phase of swallowing or criciopharyngeal spasm. Can be treated via endoscopic stapling.
Describe the Sensory and Motor Innervation of the Pharynx
Innervation of the Pharynx is by the Pharyngeal Plexus of nerves. This is formed by branches of the Vagus (CN X) and Glossopharyngeal (CN IX) nerves along with sympathetic fibres from the Superior Cervical Ganglion.
Sensory Innervation
- Nasopharynx: maxillary nerve (CN V2)
- Oropharynx: glossopharyngeal nerve (CN IX)
- Laryngopharynx: vagus nerve (CN X) [teachmeanatomy]
Motor Innervation
- All the muscles of the pharynx are innervated by the vagus nerve (CN X) via its pharyngeal branches to all muscles of the pharynx and soft palate except to:
- Exception to this is the Stylopharyngeus Muscle
- Glossopharyngeal Nerve (CN IX)
NB: Tensor veli palatine is innervated by V3 cranial nerve.
Describe the Voluntary Phase of Swallowing
Once food has been masticated and mixed with saliva to form a bolus, it must be swallowed. Swallowing is in three phases:
Voluntary Phase (deglutition)
- Masticated food bolus is transferred from the oral cavity into the oropharynx mainly by movements of the tongue and soft palate.
- Tongue and suprahyoid muscles pull hyoid and larynx up
- Soft palate elevates – nasopharynx closed off
- Superior constrictors contract
Describe the Pharyngeal Phase of Swallowing
Afferent information from pressure receptors in the palate and anterior pharynx reaches the swallowing centre in the brain stem.
A set of movements is triggered
- Inhibition of breathing
- Raising of the larynx – the elevation of the soft palate to close off the nasopharynx from the oropharynx and laryngopharynx is a reflex-driven process during which the contraction of the suprahyoid and the longitudinal pharyngeal muscles elevate the larynx.
- Closure of the glottis
- Opening of the upper oesophageal ‘sphincter’
- Automatic contraction of the three pharyngeal constrictor muscles force the food into the oesophagus - food bolus passes into hypopharynx by aid of middle and inferior constrictors.
- Larynx protected by overhanging tongue, epiglottis, vocal cords.
- Cricopharyngeus relaxes
Describe the Oesophageal Phase of Swallowing
- The muscle in the upper third of the oesophagus is voluntary striated muscle under somatic control
- The muscle of the lower two thirds is smooth muscle under control of the parasympathetic nervous system.
- A wave of peristalsis sweeps down the oesophagus, propelling the bolus to the stomach in ~9 seconds.
- Coordinated by extrinsic nerves from the swallowing centre of the brain
- Lower oesophageal ‘sphincter’ opens
Describe the blood supply to the pharynx
The blood supply of the Pharynx is via the Superior Thyroid, Ascending Pharyngeal, Ascending and Descending Palatine arteries. They are branches of the lingual, facial and maxillary arteries (branches of the ECA).
Venous Drainage of the Pharynx
Venous drainage of the Pharynx is via the Pharyngeal Venous Plexus => Internal Jugular Vein.
How are children different to adults?
The adult larynx has a cylinder shape. The infant larynx is funnel shaped because of a narrow, undeveloped cricoid cartilage.
Describe Assessment and Examination
Airway resistance: according to Poisuelle’s law, in laminar flow, the rate of flow is inversely proportional to the length and radius^4.
Microlaryngoscopy and Bronchoscopy
- Atropine premed
- Inhalational induction: Sevoflurane and oxygen
- Spontaneously breathing
- Nasopharyngeal ETT
- Lignocaine spray on vocal cords
- Laryngoscope +/- Suspension
- O degrees Hopkins rod
Describe the presentation and causes of acute epiglottis (now very rare)
Presentation
[*] Usually 2-7 years old
[*] Bacterial infection
[*] Septic/pyrexial (>38oC)
[*] Leaning forward and drooling
[*] Classic tripod position
[*] Stridor tends to be continuous and progressive => possibly fatal
Causes
[*] H. influenzae Type B (vaccine has caused decline)
[*] Staphylococci
[*] B-haemolytic streptococci
Pneumococci
