Physiology of deglutition

Dr. T. Balasubramanian

PHYSIOLOGY OF DEGLUTITION

DRTBALU'S OTOLARYNGOLOGY ONLINE 2

The crossing of alimentary and Ventilatory streams is an

Evolutionary consequenceOf transition of vertebrates

From sea to land living


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


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


ANATOMY


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.


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


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


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


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


ANATOMY OF PHARYNX• It is a midline tube about 15 cm long

• It is continuous with nasal cavities and larynx above and esophagus below

• The anterior wall of pharynx is incomplete and is composed of posterior part of tongue superiorly and larynx inferiorly

• Pharynx is hence divided into nasopharynx, oropharynx and laryngopharynx according to those structures lying anteriorly

• The reminder of pharynx resembles the gut. It has 4 layers i.e. areolar, muscular, sub mucous and inner mucous membrane (from outside inwards)

• The muscular layer has 2 components i.e. longitudinal and circular muscle layers


ANATOMY OF PHARYNX – (CONTD)• The circular muscle layer is formed by superior, middle and inferior constrictors

• The inferior constrictor has 2 components i.e. thyropharyngeus and cricopharyngeus

• Except the cricopharyngeus muscle all the other muscles acting on the pharynx are paired

• The cricopharynx forms a distinct sphincter at the point where laryngopharynx enters the oesophagus


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


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


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


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


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


NEURAL CONTROL OF SWALLOWING• Two areas of brain are involved

• Cerebral cortex

• Brain stem


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.


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


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


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


Thank you

Health & Medicine

Physiology of deglutition