physiology of deglutition by ROOHIA

Physiology of deglutition

Dr. Roohia

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Introduction• Deglutition involves co-

ordinated activity of muscles of oral cavity, pharynx, larynx and esophagus

• The whole process is partly under voluntary control & partly reflexive in nature

• Deglution by definition involves passage of bolus of food (solid / liquid) from the oral cavity to stomach via the pharynx and esophagus.

• Voluntary control of deglutition involves control of jaw, tongue, degree of constriction and length of pharynx and closure of laryngeal introitus

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Components of deglutition

•Deglution has 3 components•Passage of bolus from oral cavity to

stomach•Protection of airway•Inhibition of air entry into the stomach

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Deglutition - phases

•Oral•Pharyngeal•Esophageal

These stages have been traditionally described for the sake of convenience. They help in the better understanding of the physiological process involved.

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Oral phase• In this phase food is

prepared for swallowing Tongue plays a vital role in

this process• This phase is divided into

oral preparatory phase and oral phase proper

• This phase is vital in all land animals which don’t swallow their food as a whole

• This phase is under voluntary control

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Oral preparatory phase• This phase involves breaking down

of food in the oral cavity• During this phase the food is

chewed and mixed with saliva making it into a bolus which can be swallowed

• The elevators of lower jaw play an important role in bolus preparation

• Tongue plays a vital role in bolus formation by the action of its intrinsic muscles which alters its shape. Its extrinsic muscles changes its position within the oral cavity thereby helping in chewing the food by dental occlusion

• Occlusal action of the lips help in creating an effective seal preventing the bolus from dribbling out of the oral cavity

• The action of buccinator muscle helps in pushing the bolus out of the vestibule into the oral cavity proper

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oral preparatory phase (contd)

• SALIVARY GLANDS: Salivary glands connected

to mouth by ducts. Glands produce saliva. Saliva contains: Mucin- holds food

together. Salivary amylase- starts

digesting carbohydrates. Bicarbonates-maintain PH

level of saliva&protect teeth.

Lysozymes-inhibits bact.,growth.

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Bolus formation• This is the most important

function of preparatory phase

• This involves repeated transfer of food from oral cavity to oropharyngeal surface of tongue

• Bolus accumulates on the oropharyngeal surface of tongue due to repeated cycles of upward & downward movement of the tongue

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Oral phase proper• During this phase the bolus is moved

towards the back of the tongue• The contraction of soft palate

prevents nasal regurgitation• The soft palate also prevents

premature movement of bolus into the oropharynx

• Once the bolus is of suitable consistency the transit from mouth to oropharynx just takes a couple of seconds

• Tongue plays a vital role during this phase. Its intrinsic muscles contracts and reduces its size, while genioglossus muscle elevates the tongue towards the palate

• The elevation of the mandible plays a vital role here

• When the mandible is elevated the suprahyoid muscles raises the hyoid bone

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Pharyngeal phase (Pumping action of tongue & hypopharyngeal suction) • This phase of deglutition is reflexive in

nature• It is during this phase that Ventilatory

and alimentary streams cross each other. Dynamic separation of these streams is possible due to the co-ordination of reflex phase that occurs

• It just takes a second for the bolus to traverse the pharynx and reach the cricopharyngeal area

• Contraction of diaphragm is inhibited making simultaneous breathing & swallowing impossible

• Soft palate is elevated in order to seal off the nasopharynx (T. palatini & L. palatini)

• Vocal cords adduct protecting the airway

• As the bolus passes the palatoglossal & palatopharyngeal folds the act of swallowing becomes reflexive

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Functions of trigger points in oropharynx

• Stimulation of trigger points present in the oropharynx starts off the pharyngeal reflexive stage of swallowing

• Trigger points are present at the faucial arches & mucosa of the posterior pharyngeal wall

• These trigger points are innervated by glossopharyngeal nerve

• Stimulation of these trigger points causes dilatation of pharynx due to relaxation of the constrictors, and elevation of pharynx & larynx due to contraction of longitudinal muscles

• The pharynx constricts behind the bolus thereby propelling it

• Contraction of the inferior constrictor moves the bolus towards the oesophagus

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Importance of laryngeal elevation during pharyngeal stage

• It narrows the laryngeal inlet• It ensures better sealing of the

laryngeal inlet by the downturned epiglottis

• Laryngeal elevation also contributes to dilatation of pharynx

• The laryngeal inlet is closed due to the actions of interarytenoid, aryepiglottic and thyroepiglottic muscles

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Role of epiglottis in the pharyngeal phase

• The movement of epiglottis occurs in two stages

• The epiglottis moves from vertical – horizontal position

• The upper third of epiglottis moves below the horizontal to a slightly lower level to cover the narrowed laryngeal inlet

• The bolus during the course of the swallow impinges on the epiglottis and gets diverted to the lateral food channels

• Solid food tends to go behind the epiglottis in to the post cricoid area

• Liquid food gets split by the epiglottis and passes via the pyriform fossae

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Esophageal stage• This is purely reflexive• This phase begins by

relaxing the cricopharyngeal sphincter

• The time taken for esophageal transit is 10-15 seconds

• Primary / secondary / tertiary peristaltic waves play active roles in this phase

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Neural control of swallowing• Two areas of brain are

involved• Cerebral cortex• Brain stem

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Neural control (initiation)• Initiation of swallow is voluntary• Bilateral prefrontal, frontal and

parietal cortices are involved• Swallowing is initiated when food

comes into contact with certain trigger areas like fauces / mucosa of posterior pharyngeal wall

• Afferent nerve is the glossopharyngeal nerve

• Nucleus tractus solitarius & spinal nucleus of trigeminal nerve play a vital role

• Efferents involve several cranial nerve nuclei which include nucleus ambiguus (muscles of palate, pharynx and larynx), hypoglossal nucleus supplying the muscles of the tongue, motor nuclei of trigeminal and facial nerves supplying the muscles of face, jaws and lips.

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Role of medulla• There are two groups of

neurons in the medulla while lie between the afferent and efferent system

• First group lie in the dorsal medulla above the nucleus of the solitary tract

• The second group lie in the ventral medulla around nucleus ambiguus

• These groups of neurons are named as lateral & medial medullary swallowing centers

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Role of central pattern generator

• Central pattern generator are a set of neurons capable of initiating sequential swallow

• These neurons act like a cardiac pacemaker

• Since the process of swallowing and breathing are interlinked there is a certain degree of central co ordination taking place

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Phase of respiration & swallowing•Swallowing occurs during expiratory

phase of respiration•This helps in clearing food material left in

the vestibule. Thus it should be considered to be a protective phenomenon

•The rhythm of respiration is reset after a successful swallow

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STUDY OF SWALLOWING

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INDICATIONS FOR STUDY OF SWALLOWING

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STUDY OF SWALLOWING

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Fluroscopic imaging of swallowing

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Double contrast image of pharynx

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Examination of oesophagus

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Dc image of gastro oesophageal junction

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Analysing disorders of swallowing

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asymmetry

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Stasis

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Cricopharyngeal dysfunction

drtbalu's otolaryngology online

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Aspiration

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Web

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THANK YOU

physiology of deglutition by ROOHIA

Health & Medicine

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