SWALLOWING

what is another term for swallowing

deglutition

what is swallowing

swallowing is the action of:

• preparing food within the oral cavity

• transmitting the prepared bolus from the oral cavity through the pharynx and oesophagus to the stomach safely

how many times do we swallow in a 24h period and how many of those are associated with eating/ drinking

600-1000 (≈ 150 are associated with eating/ drinking - the rest are getting rid of saliva)

state the phases of swallowing

1. oral phase

   • oral preparatory phase

   • oral phase

2. pharyngeal phase

3. oesophageal phase

which phases of swallowing are voluntary and which are a reflex

• the oral phase is voluntary - you can choose when to swallow

• the pharyngeal and oesophageal phases are reflexes - once initiated it cannot be stopped

outline the oral preparatory phase

oral preparatory phase

• preparation of food by mastication and mixing with saliva

• consistency of food monitored by sensory receptors in oral mucosa

outline the oral phase process

• moist chewed food is collected into a bolus mainly by the tongue working against the teeth and hard palate

• the oral cavity is occluded by raising the tongue to the palate from front to back

• this pushes the bolus towards the oesophagus

• the back of the tongue is lowered to form a chute

• food is then pushed into the oropharynx by a backward tongue thrust

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» CN XII (hypoglossal nerve) provides the tongue’s motor innervation

what is the innervation of the muscles of the tongue

• all muscles of the tongue are provided motor innervation by CN XII (hypoglossal)

• except the palatoglossus which is innervated by CN X

what are the trigger points and reflexes during the oral phase of swallowing

• common trigger points:

  • palatoglossal arches/ anterior pillars of fauces

  • posterior pharyngeal wall

  • palatine tonsils

  • soft palate

• bolus contact with trigger points initiates:

  • reflex pharyngeal contraction

  • reflex actions to protect the lower airway

which nerve mediates the sensory aspect of the gag/ pharyngeal reflex

CN IX (glossopharyngeal)

what requirement is usually necessary for the oral phase to be completed

• the mouth must be closed - this elevates the mandible so the suprahyoid muscles can act on the hyoid bone much easier

• it is difficult to swallow with the mouth open

what else occurs as food moves from the mouth to the pharynx

uncertainty as to when certain actions occur as food moves from mouth to pharynx:

• elevation of soft palate (CN X) to stop food entering nasopharynx and nose

• temporary suspension of respiration to minimise inhalation of food into larynx as it passes through the pharynx

outline the main actions of the pharyngeal phase

• passage of food through pharynx

• protection of lower airway to prevent inhalation of food

• passage of bolus by sequential contraction of three pairs of pharyngeal constrictor muscles - innervated by CN X except the stylopharyngeus (CN IX)

what is the lower region of the inferior pharyngeal constrictor muscle also known as

cricopharyngeus - attached to the cricoid cartilage

what is the upper region of the inferior pharyngeal constrictor muscle also known as

thyropharyngeus - attached to the thyroid cartilage

what occurs in the pharyngeal phase to protect the lower airway

• suspension of respiration

• elevation of larynx by suprahyoid muscles

• narrowing of laryngeal entrance - cannot be closed off but can be narrowed by action of aryepiglottic muscles (weak)

• strong adduction of vocal folds

describe the process of laryngeal elevation during the pharyngeal phase of swallowing

• suprahyoid muscles contract which pulls the hyoid bone upwards

• the larynx is connected to the hyoid bone (via the thyrohyoid membrane) therefore the larynx is also elevated

• the epiglottis flips backwards to cover the laryngeal entrance

• epiglottis is convex anteriorly so food is directed laterally away from laryngeal entrance into pyriform recesses

which muscles adduct the vocal folds during the pharyngeal phase of swallowing

• interarytenoids

• lateral cricoarytenoids

describe the process of the pharyngeal phase

• food passes through the pharynx by muscular action

• deflected by epiglottis to bypass narrowed and elevated laryngeal entrance

• respiration is suspended

• rima glottis is closed to prevent anything that does enter the larynx from passing further

• cough reflex if food does enter the larynx

which nerve stimulates the cough reflex

superior laryngeal branch of CN X

outline the oseophageal phase

• food is passed down the oseophagus to the stomach by the action of the oesophageal muscles

how long does swallowing take, why is this?

swallowing takes 1.5-2s and needs to be this fast because respiration is suspended

what is the purpose of coughing

to expel mucus or foreign bodies from the respiratory system

what is the cough reflex initiated by

noxious stimulation of the pharynx, larynx or bronchial passageway - sensory limb of the CN X

what happens during the cough reflex

• diaphragm and intercostal muscles contract

• vocal folds adduct

• glottis closes

• expiratory muscle contracts

• bronchi and non-cartilaginous portions of the trachea collapse

when does the gag reflex occur

if a swallowing reflex is elicited but the stimulating material cannot be swallowed

what occurs during the gag reflex

• the mouth is opened and posterior part of the tongue is elevated in attempt to expel the material

• at the same time the soft palate is elevated to stop material entering the nasopharynx

which nerves are involved in the sensory aspect of swallowing

CN V

• sensory to mouth and lips

CN IX

• sensory to pharynx

• initiates reflex phases of swallowing

which nerves are involved in the motor aspect of swallowing

CN V₃

• muscles of mastication and suprahyoids

CN VII

• muscles of facial expression (lips)

CN X

• muscles of soft palate, pharynx and larynx

CN XII

• muscles of tongue

what is dysphagia

any abnormality of swallowing

what are causes of dysphagia

• obstructive

• neurogenic

• xerostomia

outline obstructive causes of dysphagia

• space occupying lesions e.g. cancer

• occlusion by enlargement of adjacent structures esp. oesophagus

  • can also be heart, great vessels, bronchi

outline neurogenic causes of dysphagia

• interference with neuromuscular mechanisms of swallowing by neuromuscular disease e.g. stroke, Parkinson’s, motor neurone disease

• can cause direct damage to cranial nerves

• can cause damage to control centres of swallowing (stroke)

outline effects of neurogenic dysphagia

• swallowing is slow and difficult

• phases become uncoupled so there may be poor transit - can lead to food pooling

• food pooling increases the chances of aspiration

outline xerostomic causes of dysphagia

• can be due to radiotherapy, medications, other conditions like Sjogren’s

• consistency of saliva is also important - not just quantity

how is swallowing controlled

• swallowing centres in brainstem coordinate the actions of cranial nerves and respiration

• higher centres in insular cortex - some evidence of lateralisation

what problems are caused by dysphagia

• malnutrition

• social problems

• aspiration of food or drink into lower respiratory tract

what happens if food enters the (normal) larynx

superior laryngeal nerve (CN X) elicits cough reflex

outline silent aspiration

• if the laryngeal mechanism is compromised (no sensation/ muscle weakness) food may be inhaled without a cough reflex

  • this is silent aspiration

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• foodstuff enters the bronchial tree and stagnates

• it may become infected - infection is more likely if food is carrying bacteria from a mouth with poor oral hygiene

• this can lead to pneumonia and death

how is swallowing clinically tested

bedside test:

• take sips of water - assess timing of swallow, size of sip

• assess to see if the patient stops drinking, cough, choke or have a “wet voice”

  • wet voice = fluid build up on vocal folds - indicates aspiration

what techniques can be used to assess swallowing

• fiber-optic endoscopic evaluation of swallowing (FEES)

• video fluoroscopy (VFS) - specialised type of radiograph