What Do The Pharynx And Esophagus Add To The Process Of Swallowing?
The process of swallowing (Effigy ane) includes the witting endeavor to ingest food and the largely hidden (reflex) efforts of preparing the bolus to be swallowed (preparatory stage), transferring or transporting of the bolus from oral and pharyngeal passages to the esophagus (oropharyngeal transfer or transport phase), and transporting of the bolus through the esophagus to the stomach (esophageal ship phase).
Figure i: Diagrammatic analogy of motor events of swallowing reflex.
a. Illustrates the onset of the swallowing reflex. Information technology shows tip of tongue in contact with anterior office of palate. Bolus is pushed backward in groove betwixt natural language and palate. Soft palate is being drawn up. b. Bolus has reached the vallecula. Hyoid bone and larynx move upwardly and forward. Epiglottis is tipped downwardly. Contraction wave on posterior pharyngeal wall moves downward. c. Soft palate has been pulled downwardly and approximated to root of tongue by contraction of pharyngopalatine muscles, and past pressure of descending pharyngeal contraction wave. Cricopharyngeus muscle is opening to permit entry of bolus into esophagus. Trickle of food enters also laryngeal opening but is prevented from going farther past closure of ventricular folds. d. The contraction wave has reached vallecula and is pressing out last of bolus from them. The bolus has largely passed through the upper sphincter into esophagus. e. Contraction moving ridge has passed pharynx. Epiglottis is beginning to turn upward again as Hyoid bone and larynx descend. Communication with nasopharynx has been re-established. f. All structures of pharynx have returned to resting position. (Source: Netter medical illustrations with permission from Elsevier. All rights reserved.)
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Physiology of the Oral Phase of Swallowing
Functional Description
The oral stage includes all swallowing activities that occur within the oral crenel. Information technology can be divided into preparatory and transfer phases. The mouth is bounded by the lips anteriorly; the cheeks laterally; the teeth, alveolar ridge, difficult palate, and soft palate anteriorly; the teeth, alveolar ridge, floor of mouth, and natural language inferiorly; and the soft palate, uvula, tonsillar pillars, and posterior part of the natural language that class the posterior opening of the oral cavity or the oropharyngeal isthmus.
Ingestion of a bolus usually requires active lowering of the mandible, opening of the lips, and low of the tongue—actions that increase the size of the oral fissure to accommodate the ingested bolus. During ingestion by sucking, such as with a harbinger, the lips remain sealed around the delivery vessel and the exit to the back of the oral cavity is closed by the tongue and soft palate. Lowering of the mandible along with depression and retraction of the tongue are accompanied by bracing of the cheeks and mouth floor. These actions generate a subatmospheric pressure level inside the oral crenel that facilitates period of fluids into the oral cavity. Such suction may also serve to drive entry of saliva into the oral cavity from the salivary glands.
Mastication is necessary for rendering solid ingested boluses into a size, shape, and consistency that is amenable to transport. This activeness requires complex variations in the force and velocity of mandibular move, holding and grinding solids with the teeth. During this process the cheeks and tongue office to position the solid over the grinding surfaces. The tongue also helps reduce softer or dissolvable solids by mashing them against the bony structures bounding the oral fissure and mixing them with liquid elements of the ingested bolus. Secreted saliva also facilitates dissolving and lubricating solid boluses and is the major stimulus for the basal eat rate between periods of ingestion.
Once the bolus has been adequately prepared it is positioned in a recess on the dorsum of the tongue, primarily by action of the tongue, just with assistance for some boluses by action of the muscles that move the lips, cheek, oral cavity floor, and mandible. The oropharyngeal isthmus open as the transfer phase begins. Not all of the oral crenel contents are necessarily transported together in a single swallow. The bolus is frequently partitioned, with that part not transported remaining within the oral anteroom or on the floor of the oral fissure. Indeed, in the process of normal combined eating and drinking, solid and liquid bolus material may even enter the pharynx before onset of the oral transfer phase of the majority of swallows.
At the showtime of the oral transfer phase the superior perimeter of the tongue is pressed against the hard palate, sealing the bolus from the anterior mouth. Especially with large liquid boluses, the posterior aspect of the tongue and soft palate are closed together to prevent premature spill of the bolus into the throat. In a rapid sequence, the natural language presses against the hard palate, generating a pressure moving ridge directed posteriorly that propels the bolus into the oropharynx. The forcefulness of this natural language activeness tin be volitionally modified. Concurrent with this activity, the soft palate elevates, while the cheeks, floor of mouth, and jaw are braced. The oral phase can be considered completed when the bolus tail enters the oropharynx, at which point the posterior dorsum of the natural language remains sealed against the soft palate to prevent retrograde escape of bolus back into the oral cavity.
Part of Muscles and Motor Nerves
Several muscle groups participate in the oral stage of swallowing (Tables 1, 2, 3, 4, 5, vi). All of these are striated muscles using acetylcholine for neurotransmission via nicotinic receptors. The cell bodies of the motor neurons supplying these muscles are located in brainstem nuclei located in the pons (trigeminal, facial) and medulla (nucleus ambiguous, hypoglossal) or in the anterior horn of the cervical spinal string (C1-2). Figures 2 and iii are illustrations of lateral and anterior-posterior views of the origins of these cranial nerves. Axons from these motor neurons travel via cranial nerves (CNs) V, VII, Nine to XII, and the ansa cervicalis.
Figure 3: Origin of cranial fretfulness involved in swallowing.
This illustration shows an anterior-posterior projection of cranial nerve nuclei. Left half illustrates sensory nuclei and correct half shows motor nuclei. Note that the cranial nerve X is connected with the sensory nucleus (nucleus tractus solitarius, NTS) and motor nucleus to striatal muscles of the pharyngeal and larynx (nucleus ambiguous, NA). Dorsal motor nucleus of the vagus (DMV) contains preganglionic nerves that supply smooth muscle of the esophagus and the rest of the gut. (Source: Netter medical illustration with permission of Elsevier. All rights reserved.)
Muscles in the facial group are supplied by CN VII (Figure 4). During mastication they office to seal the oral fissure and position food over the grinding surfaces of the teeth. The muscles of mastication are supplied past CN V. Their actions move the mandible during chewing, providing the force for grinding food. During the oral ship phase action by muscles in this grouping to heighten the mandible counter the push of the tongue against the hard palate.
The intrinsic muscles of the tongue are supplied by CN XII. They have no bony attachments. Because muscle tissue is incompressible, the muscles of the tongue role as a hydrostat, wherein changes in shape do non result in a change in volume. For instance, contraction of the transverse muscle of the tongue non only narrows the tongue simply likewise lengthens it. The extrinsic muscles of the tongue take their origin on various bony structures and insert into the natural language. Similar the intrinsic tongue musculature, their innervation is via CN XII. Although the palatoglossus muscle tin also be considered an extrinsic tongue muscle, its different embryonic origin (fourth pharyngeal arch) and innervation (nucleus cryptic) propose more advisable placement in the palatal group. Deportment of the extrinsic muscles elevate, depress, protrude, and retract the tongue.
The suprahyoid muscles overall act to raise the hyoid bone and larynx, whereas the infrahyoid muscles have the opposite action. The suprahyoid muscles are supplied past motor neurons located in the trigeminal and facial nuclei in the pons, with the exception being the geniohyoid, which, along with the infrahyoid group, is supplied by motor neurons within the anterior horn of the upper cervical spinal string. During the oral phase, these two groups act in concert to stabilize the position of the hyoid, whereas those suprahyoid muscles with antagonistic action tense the floor of the mouth when acting together. These deportment provide a stable base to resist the forces generated by the natural language contracting against such structures as hard palate and teeth. Thus, these muscles can be active during the both preparatory and transport phases of swallowing.
The palatal musculus group is innervated from motor neurons residing in the trigeminal nucleus or nucleus ambiguous. These muscles human activity during the oral phase of deglutition to stiffen the soft palate, lower the soft palate to prevent premature bolus spill into the pharynx, or elevate the soft palate to open the oral cavity posteriorly.
Role of Afferent Nerves
Sensory input is disquisitional to the oral phase of swallowing, because assessment of the chemical and physical properties of the bolus at this point allows gear up expulsion of boluses with noxious backdrop. Sensory feedback is likewise required during bolus training and transport to permit appropriate positioning of oral structures; attune the forcefulness, velocity, and timing of muscle contractions; and determine the position and readiness of the bolus for transport. Some sensory pathways subserve protective reflexes, such equally the gag reflex. Finally, stimulation of certain sensory receptive fields acts to initiate, or facilitate the initiation of, deglutition.
Afferent sensory neurons of import in the oral phase of swallowing travel in CNs V, Vii, 9, and Eleven (Effigy v). Gustation sensation is conveyed by special visceral afferent fibers from the anterior two thirds of the tongue (CN Vii), the posterior 3rd of the tongue (Nine), and epiglottis (Ten), with these fibers terminating in the nucleus tractus solitarius (NTS). Sense of taste data is conveyed rostrally from the NTS to the thalamus, insula, and hypothalamus. Sensations of light impact, temperature, pressure, pain, musculus stretch, and proprioception for most of the oral cavity and the anterior ii thirds of the natural language are conveyed from fibers that ascend in CN V. These fibers finish in the mesencephalic (stretch, proprioception), spinal (hurting, temperature), and main sensory (touch, pressure) nuclei of CN 5. General somatic afferent innervation of the posterior third of the tongue and the faucial pillars ascends through CN 9 to the NTS. Some neurons that synapse in the NTS also send axons rostrally to the pons and cortex.
The importance of sensory input for the initiation of the oral transport stage of deglutition is self-evident by noting the maximal swallowing frequency that tin be obtained while drinking a glass of water at the fastest possible rate compared to the lower sustainable deglutitive rate observed with dry swallows. Because of the large degree of cortical input to the oral phase of swallowing, trivial data exists regarding the receptive fields and sensory stimuli that facilitate the onset of oral send. Boluses placed on the posterior tongue (glossopharyngeal innervation) trigger swallowing at a lower book than on the anterior tongue (trigeminal innervation), with acid boluses having the lowest threshold. Once the ship stage is triggered, sensory data regarding bolus book and consistency modifies the musculus action.
Central Nervous System Control
Spontaneous, swallowing occurs about in one case per minute in the awake state, is greatly reduced during slumber, and increases during emotional stress. Damage to different areas of the cortex can result in difficulties with mastication and the initiation of swallowing. These observations underline the importance of cortical and cognitive input to the oral phase of swallowing.
Studies on the central command of the oral phase of swallowing have identified a cortical region, the stimulation of which provokes rhythmic jaw and natural language action consequent with mastication. At the brainstem level in that location is testify for a fundamental pattern generator for repetitive masticatory activity, which appears to involve neurons located in the primary trigeminal sensory nucleus and medial pontobulbar reticular germination. In humans, functional imaging studies have identified multiple regions above the brainstem that are active during mastication, including the cortex (sensorimotor, prefrontal, supplementary motor expanse, insula), thalamus, and cerebellum. Subjects with a chewing side preference show ascendant activeness in the contralateral sensorimotor cortex during natural language movement. Masticatory activities are inhibited past induction of swallowing.
Multiple cortical areas including the sensorimotor, insular, prefrontal, anterior cingulate, parieto-occipital cortex, along with the amygdala, thalamus, basal ganglia, and cerebellum have been shown to be activated during voluntary swallowing. An of import observation in well-nigh of these studies is that, although activity is bilaterally represented, there is laterality of activity seen in an inconsistent distribution amongst subjects. The effect of study constraints (e.g., subject confinement/restraint, bolus commitment) on the areas activated is unknown.
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Physiology of the Pharyngeal Phase of Swallowing
Functional Clarification
The pharyngeal phase descriptively is that period from when the swallowed bolus commencement enters the pharyngeal cavity until the bolus tail exits the UES. Anatomically, the pharynx can exist divided into the nasopharynx (above soft palate), oropharynx (from soft palate to pharyngoepiglottic fold), and hypopharynx (pharyngoepiglottic fold to cricopharyngeus musculus). During the pharyngeal phase, three of the potential exits (upper airway, rima oris, and lower airway) must close while the bolus is rapidly propelled into the 4th (esophagus). Closure of these passages results in trapping of approximately 15 mL of air inside the pharyngeal infinite, which is so also transported along with the bolus into the esophagus during isolated single swallows. The time from bolus entrance to bolus go out from the pharynx is slightly less than ane second (Figure 1). This time is longer for larger boluses, due to before archway into the pharynx from the start of the consume. The forceful backward thrust of the tongue accelerates the bolus head apace. With larger bolus volumes, velocity at the level of the UES may exceed 30 cm/sec, whereas velocities of solid particles may approach 40 cm/sec in the supraglottic region (Figure 2). These are much faster velocities than those that are observed at the tail end of the bolus, which average around 10 cm/sec. Passage of the bolus tail temporally approximates the passage of the meridian pressure level moving ridge that occludes the pharyngeal lumen at that level. All of these velocities are faster than those of the peristaltic stripping moving ridge in the esophageal trunk (1 to 4 cm/sec) and likely reflect the need to articulate the pharynx quickly and then that respiration can resume.
During the pharyngeal stage of swallowing the tongue maintains a position against the palate to seal the oropharynx. The soft palate elevates and the proximal pharyngeal walls motion medially to seal off the nasopharynx. The vocal cords and arytenoids are adducted, the adducted arytenoids motility to the base of the epiglottis, and the epiglottis swings down to cover the laryngeal foyer. These actions seal the airway from the pharyngeal cavity. With larger boluses, the bolus head reaches the level of the laryngeal vestibule earlier the epiglottis has completed its downward descent and is channeled around the larynx into the piriform recesses. In addition the hyoid bone and larynx move superiorly and anteriorly, bringing the larynx to a position under the base of the tongue, and out of the path of the bolus as it descends through the pharynx. The throat too widens and shortens, which is accompanied past an elevation of the UES by 2 to 2.5 cm.
The pharyngeal phase can be seen every bit a continuation of the oral ship phase of deglutition. However, swallows tin can as well be initiated at the pharyngeal level, wherein no bolus is transported from the oral cavity. These reflexive or pharyngeal swallows are in response to pharyngeal stimulation, such as due to accumulated food or saliva. With a sufficient level of stimulation, these reflexive swallows appear to be irrepressible.
Office of Muscles and Motor Nerves
All of the muscles involved in the pharyngeal phase of swallowing are striated muscle and use acetylcholine as their neuromuscular transmitter via nicotinic receptors. The cell bodies of the motor neurons supplying these muscles reside in brainstem nuclei located in the pons (trigeminal) and medulla (nucleus cryptic, hypoglossal) or in the anterior horn of the cervical spinal cord (C1-2). Axons from these motor neurons travel via cranial nerves V, IX to XII, and the ansa cervicalis (Tables 1-6).
The intrinsic and extrinsic muscles of the natural language continue the activeness initiated in the oral phase. As the tail of the bolus clears the oral crenel, the dorsum of the tongue remains compressed confronting the difficult and soft palate, thus preventing retrograde bolus escape dorsum into the mouth. Action of the palatopharyngeus muscles to approximate the palatopharyngeal folds may help seal the oral crenel. In addition, the back of the tongue is compressed forcefully against the back of the oropharynx, clearing the bolus into the hypopharynx. The tongue remains pressed against the back of the oropharynx usually until the bolus tail exits the hypopharynx. The tongue so moves frontwards to open the passage to the airway.
The muscles in the palatal group act to tense and elevate the soft palate to seal the archway from the oropharynx to the hypopharynx. The upper portion of the superior pharyngeal constrictor also contracts to shut the pharynx medially as office of the nasopharyngeal seal. The soft palate elevation is maintained until the bolus tail exits the hypopharynx, after which the soft palate unremarkably returns to a rest position.
The muscles of the pharynx tin can be divided into ii functional groups, based on their activeness. Contraction of the longitudinal group (palatopharyngeus, stylopharyngeus, salpingopharyngeus) elevates and shortens the pharynx. The activity of the stylopharyngeus as well widens the throat and opposes anterior move of the posterior pharynx. The deportment of these muscles elevate the larynx as well. Muscles in the circular group (superior, center, inferior constrictors) have fractional overlap at their borders. Contraction proceeds in an aboral direction to clear the trailing portion of the bolus into the esophagus. All of the pharyngeal muscles have their motor neurons located in the nucleus cryptic and are innervated via the pharyngeal plexus, except for the stylopharyngeus (CN IX) (Figure vi). Distribution of the vagus (CN 10) nerve is show in Figure 7 (Figure 7).
The office of the muscles in the suprahyoid and infrahyoid groups changes as the swallow progresses from the oral preparatory to the oral and pharyngeal ship phases. Deportment of the infrahyoid grouping are inhibited, so that the suprahyoid group can heighten the hyoid bone forth with the larynx and move them anteriorly. Considerable variation as to which suprahyoid muscles are activated exists amid individuals. The 1 infrahyoid muscle that remains active is the thyrohyoid, which moves the thyroid cartilage to the base of the hyoid, thus farther elevating the larynx.
The intrinsic muscles of the larynx function to close the glottis and supraglottic infinite, approximating the arytenoids cartilages to the base of the epiglottis. The timing of these events is controversial amidst studies. Some studies report that activation of intrinsic laryngeal muscles occurs later onset of suprahyoid, superior constrictor contractions, and laryngeal elevation and activity in the submental muscles. On the other hand, visual onset of vocal string closure occurs before onset of action in the submental muscles. Song cord closure occurs before the closure of the laryngeal vestibule by the downward movement of the epiglottis. Downwards move of the epiglottis to a horizontal position depends on forces transmitted via the ligament betwixt the epiglottis and hyoid as the hyoid moves anteriorly and superiorly. Further downwardly movement to close the anteroom mostly results from passive compression of the epiglottis past the onrushing bolus and pharyngeal constrictor contraction, although in some individuals the aryepiglottic muscle may facilitate epiglottic movement. Passage of the bolus into the esophagus is followed by opening of the antechamber, generally from elastic recoil of the epiglottis, and and then opening of the glottis by the posterior cricoarytenoid muscle. All of the intrinsic laryngeal muscles involved in deglutition have their motor neurons in the nucleus cryptic, and the axons laissez passer through the inferior laryngeal co-operative of the recurrent laryngeal nerve (CN Ten).
Role of Afferent Nerves
Sensory modalities present in the oral crenel are likewise nowadays in the pharynx and larynx. Nonetheless, the laryngopharynx has more than costless nerve endings in the mucosa and more than slow adapting mechanoreceptors. The maxillary partition of CN V supplies part of the nasopharynx and soft palate. Sensation to the oropharyngeal mucosa is as well supplied by CN Ix. Three branches of the vagus (CN 10) supply the laryngopharynx. The pharyngeal branch supplies the mucosa overlying the levator veli palatini and superior and middle pharyngeal constrictors. The internal branch of the superior laryngeal nerve supplies the hypopharynx, epiglottis, and supraglottic laryngeal structures. The recurrent laryngeal branch supplies the subglottic larynx and junior constrictor. The neurons for these regions synapse within the NTS.
Activation of receptive fields supplied by CN IX and X can trigger reflexive, or pharyngeal, swallows. Receptive fields supplied by the superior laryngeal nerve have the lowest threshold for initiating a swallow. For virtually receptive fields the charge per unit of elicitation of swallowing depends on the strength of the force per unit area stimulus, and dynamic stimuli (due east.g., vibration, stroking) are more effective than static stimuli. Within the larynx and pharynx, water is an effective stimulus for swallowing. Those neurons that synapse with the NTS or adjacent reticular formation trigger swallowing.
Sensory feedback modulates muscular function during the pharyngeal stage of swallow. This is manifest past alterations in timing and magnitude of neuromuscular events. Both bolus volume and consistency can modulate activity, depending on the parameter measured.
Central Nervous System Control
The network of neurons that establish the swallowing blueprint generator (SPG) that controls the pattern and sequence of activation of the muscles that carry out the swallowing activeness is located in the medulla. The SPG conveniently lies within the NTS, which is the primary sensory relay for the sensory information from the throat and also receives cortical input. Neurons of the SPG send projections to the lower motor neurons for the oral and pharyngeal muscles. The activity of the SPG is coordinated with other medullary reflexes. For example, it is difficult to elicit a consume when the cortical masticatory centers are stimulated. The timing of deglutition in response to pharyngeal water stimulation can be volitionally modified. Also, the incidence and relative timing of activation of various deglutitive muscles varies between individuals and between swallows in the same individual.
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Physiology of the Upper Esophageal Sphincter
Functional Anatomy and Neuromuscular Arrangement
The UES is defined manometrically as a region of elevated intraluminal pressure located at the juncture of the hypopharynx and cervical esophagus. On manometry the length of this high pressure zone is usually 2 to 4 cm. Combined manometric and fluoroscopic studies locate the superlative of this loftier-pressure level zone about 1 cm beneath the level of the vocal cords and adjacent to the C5 and C6 vertebral bodies. This location corresponds to that of the cricopharyngeus muscle. The cricopharyngeus muscle is C-shaped muscle, whose ends attach anteriorly to the cricoid lamina. Contraction of its fibers acts to close the lumen, compressing information technology against the cricoid cartilage. Studies suggest that the lowermost portion of the inferior pharyngeal constrictor contributes to the upper part of the UES. It is unclear whether the uppermost portion of the cervical esophageal muscle also contributes to the lowermost part of the sphincter.
The cricopharyngeus has a high proportion of slow-twitch, highly oxidative fibers, which back up the capability of sustained action. Other features are a high elastic tissue content and the generation of maximal agile tension at nearly twice its resting length. The cricopharyngeus also generates a passive tone in response to stretch. The cricopharyngeus is composed of striated muscle using acetylcholine via nicotinic receptors for its neurotransmission. The motor neurons are in the nucleus ambiguus. In that location is withal controversy about the precise pathways over which efferent axons travel to reach the cricopharyngeus, due to possible species differences and limitations in study technique. Bachelor evidence in humans suggests that the pharyngeal plexus (pharyngeal branch of CN 10) and recurrent laryngeal nerve provide a dual ipsilateral innervation to the cricopharyngeus.
Afferent sensory neurons from the UES have their cell bodies in the nodose ganglion and synapse in the NTS. A Golgi tendon organ-like construction nigh the insertion of the cricopharyngeus on the cricoid cartilage may provide feedback on the state of tension in the muscle. Afferent pathways from adjacent structures too participate in reflexes that modulate UES tone.
Modulation of Basal Tone of the Upper Esophageal Sphincter
When not occupied by antegrade or retrograde bolus transport, the UES remains closed. This closure helps prevent violation of the airway by retrograde passage of esophageal or gastric contents. Information technology too prevents diversion of air into the esophagus during respiration. Dissimilar smooth muscle sphincters, the UES does not exhibit a constantly agile tone at balance. Basal tone depends on the level of activity of the motor neurons, which in turn depends on input from afferent sensory and cortical pathways. Force per unit area in the UES falls during slumber and anesthesia. During such periods a basal intraluminal pressure can be observed, which probable results from the passive elastic tissue backdrop of the sphincter or pinch from adjacent structures. Basal force per unit area in the UES varies widely from infinitesimal to minute. Force per unit area in the UES increases during speech, acute emotional stress, and agitation. Movement of a catheter through the sphincter also transiently elevates sphincter pressure. Force per unit area or h2o stimulation of the pharynx too increases UES pressure, as does stimulation of the larynx with air puffs.
Upper Esophageal Sphincter Office During Deglutition
During deglutition the UES converts rapidly from a closed state to an open country to let passage of the swallowed bolus into the esophagus. During this opening the lumen assumes an oval cantankerous section. It then closes as the bolus leaves the pharynx. Because of its attachment to the larynx, which moves upward with deglutition, the UES moves upward 2 to 2.five cm.
Several factors contribute to opening of the UES. There is a autumn in the intraluminal pressure within the UES. In part this is due to an inhibition of the tone of the UES, as observed on electromyography (EMG), that lasts for about 300 to 600 milliseconds (ms). In add-on, the action of the geniohyoid, mylohyoid, and thyrohyoid muscles to pull the larynx forward indirectly exerts inductive traction on the UES. Indeed, activation of these muscles can decrease intraluminal pressure within the UES even when the tone is not inhibited. In addition, the force per unit area applied past the onrushing bolus tin push open the lumen of the UES. Thus, it is possible for the UES to relax without opening and open without relaxing. Although much of the activeness of the UES during deglutition appears stereotyped, its function can be modified by sensory feedback from the swallowed bolus. With larger boluses, the UES force per unit area relaxes earlier and longer and the UES lumen opens longer and wider. The duration of UES opening during deglutition can too be modified volitionally.
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Interactions Between the Oropharynx and Upper Digestive Tract
With deglutition, the oropharynx transfers boluses to the esophagus and thence to the stomach. Material can also travel retrograde from the tummy and esophagus dorsum to the oropharynx. Careful coordination of neuromuscular role during transit in both directions is disquisitional to forestall harm of structures and aspiration of material into the airway.
Pharyngoesophageal and Laryngeal Reflexes
Stimulation of the hypopharynx exerts a powerful inhibitory effect on the esophagus and the LES. Small amounts of fluids in the pharynx tin benumb ongoing peristaltic waves in the esophagus and result in isolated relaxation of the LES when there is no peristalsis. This reflex is mediated by long vagovagal pathways.
Reflux of liquids from the stomach to the esophagus occurs normally subsequently a meal. If this liquid refluxate were to enter the oropharynx, information technology could result in aspiration. Distention of the esophagus at rates slower than those that occur with air commitment during a belch results in contraction of the UES, particularly when the proximal esophagus is distended. During a gastroesophageal reflux event, the UES pressure increases more than the increase in intraesophageal pressure, thus preventing passage of material into the pharynx. It is controversial whether distention of the esophagus with acid enhances this response. Distention of the esophagus is also associated with closure of the vocal cords as an added airway-protective mechanism. Finally, stimulation of the hypopharynx with water results in vocal cord closure, a reflex mediated by CN 9 that can serve to prevent aspiration from refluxed liquids or boluses that fail to articulate the esophagus during deglutition.
Pharynx and Upper Esophageal Sphincter During Belching
During the human activity of belching gas passes abruptly from the tummy into the esophagus, causing precipitous esophageal distention. The passage of gastric gas under pressure is facilitated by the LES, which remains open up, and frequent contractions of abdominal muscles occur during belching. The esophageal distention results in neurally mediated reflex relaxation. The UES opening results from the reflex response and as well from the pressure of the gas existence forced out through the sphincter. The UES response to belching is of slower onset and longer duration than that seen with deglutition. The UES pressure fall results from both a true inhibition of sphincter tone as well as anterior traction on the sphincter past the suprahyoid muscles that pull the hyoid and larynx forward. The vocal cords close before the onset of UES opening, thus preventing inadvertent aspiration of liquid contents that might accompany the expulsion of air.
Pharynx During Vomiting
During vomiting textile is quickly expelled from the stomach through the esophagus and oropharynx. In the initial phase of vomiting the constrictor muscles of the pharynx are relaxed and the pharyngeal dilator muscles are contracted. The UES is relaxed and pulled open up past the muscles that move the hyoid and larynx superiorly and anteriorly. The vocal cords are actively closed to prevent aspiration.
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Interactions between Oral Crenel, Throat, and Respiratory System
In humans, evolutionary changes in the anatomy of passages that subserve respiration, swallowing, and spoken language has resulted in a common chamber for intake of air and food and for speech. Every bit a result, humans take lost the chapters to consume and exhale or speak at the same time. This has necessitated the evolution of neural control systems to coordinate swallowing and respiration. Many of the muscles that are involved in deglutition besides participate in respiration. There are non split up motor neuron pools for each part. Motor neurons for a given musculus can be active during both processes. Coordinated control betwixt the swallowing and respiratory centers is conveyed through interneurons.
Most swallows occur during the expiratory phase of respiration. During swallowing, the vocal cords are apposed and respiration is interrupted. Afterward deglutition, respiration is resumed in the expiratory stage. The direction of airflow with expiration would aid forestall aspiration of whatsoever bolus material prematurely spilled from the oral crenel earlier the swallow or left behind in the hypopharynx subsequently a eat. This coordination is contradistinct by stress on the deglutitive or respiratory systems. With chop-chop repeated swallows, respiration is more than likely to halt and resume with inspiration. As well, in the presence of increased respiratory loads and changes in lung volume, swallowing may be associated with halting and resumption of swallowing during inspiration, thus predisposing to aspiration.
During inspiration the UES pressure level increases, which serves to direct airflow into the larynx instead of the esophagus. During inspiration, the resulting subatmospheric pressure could collapse the airway. This possibility is countered past the activeness of those oropharyngeal muscles capable of dilating the airway, such equally the genioglossus and stylopharyngeus, and tensor veli palatini. During expiration, activation of muscles such equally the pharyngeal constrictors can modulate the resistance to airflow.
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