PHYSIOLOGY OF THROAT

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PHYSIOLOGY OF THROAT:

PHYSIOLOGY OF THROAT

Introduction:

Introduction The throat is the anterior part of the neck , which lies in front of the vertebral column . Or The front of the neck below the chin and above the collarbone. It primarily consists of the pharynx and larynx .

Physiology of Pharynx:

Physiology of Pharynx Deglutition Respiration Voice resonance Defence Middle ear ventilation Taste Sensation

Deglutition:

Deglutition

Stages of Deglutition:

Stages of Deglutition Deglutition can be divided into three stages: Voluntary Oral stage Pharyngeal Stage Esophageal Stage

Voluntary Oral stage :

Voluntary Oral stage Movement of the swallowing depends on the consistency of the material swallowed. Solid – chewed,mixed with saliva,made into appropriate size bolus Liquids-poured/sucked into and is maintained as bolus Lip closure Rotary/lateral jaw and tongue movements When the food is easy ready for swallowing ,it is voluntarily squeezed /rolled posterierly into the pharynx by pressure of the tongue upward and backward against the palate . From here on swallowing becomes entire automatic

Pharyngeal stage :

Pharyngeal stage As the bolus of food enters the posterior of the mouth and pharynx It stimulates epithelial swallowing receptors areas present all around the opening of the pharynx,especially on the tonsillar pillars and impulses from these passes to the brain stem to initiate a series of automatic pharyngeal muscle contraction The soft palate is pulled upwards to close he posterior nares,in this way preventing reflux to food into the nasal cavities The palatopharyngeal folds on each side of pharynx are pulled medially to approximate each other. These folds form a sagittal slit through which the food must pass into the posterior pharynx

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The vocal cords of the larynx are strongly approximated and the larynx is pulled upwards and anteriorly by the neck muscles, These actions combined cause the epiglottis to swing backwards to prevent the passage of food into the nose and trachea The upward movement of the larynx also pulls up and enlarges the opening of the esophagus, or pharyngoesophageal sphincter At the same time the upper 3-4cm of the pharyngoesophageal sphincter relaxes thus allowing the passage of the food to move easily and freely from the posterior pharynx into the upper esophagus.

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The upward movement of the larynx also lifts the epiglottis out of the main stream of food flow,so that the food mainly passes on each sides rather than over the surface of the epiglottis. This movement acts as protection against the entry of food into the trachea. Between swallows this spincter remains strongly contracted,thereby preventing air from going into the esophagus during respiration At the same time that the larynx is raised and the pharyngoesophageal sphincter is relaxed the entire muscular wall of the pharynx contracts, beginning in the superior part of the pharynx and spreading downwards as a rapid peristaltic wave over the middle and inferior pharyngeal areas,which propels the food into the esophagus .

Effect of the pharyngeal stage of swallowing on respiration :

Effect of the pharyngeal stage of swallowing on respiration The entire pharyngeal stage of swallowing occurs in less than 2 seconds thereby interrupting respiration for only a fraction of a usual respiratory cycle.the swallowing center specially inhibits the respiratory center of the medulla during this time halting respiration at any point in its cycle to allow swallowing to proceed.

Esophageal stage of swallowing :

Esophageal stage of swallowing The esophagus functions primarily to conduct food rapidly from the pharynx to the stomach. The esophagus normally exhibits two types of peristaltic movements :primary peristalsis and secondary peristalsis . Primary peristalsis is a simple continuation of the peristaltic wave that begins in the pharynx and spreads into the esophagus during the pharyngeal stage of swallowing,which takes about 8-10 secs . If the primary wave fails to move into the stomach all the food that has entered the esophagus, secondary peristaltic waves result from the distention of the esophagus by the retained food and these waves continue until all the food has emptied the stomach

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These secondary peristaltic waves are initiated partly by the intrinsic neural circuits in the myenteric nervous system and partly by reflexes that begin in the pharynx , then are transmitted upwards through vagal afferent fibers to the medulla and the back again to the esophagus through the glossopharyngeal and vagal efferent nerve fibers. The musculature of the pharynx and upper third of the esophagus is striated muscle.therefore the waves in these region are controlled by skeletal nerve impulses from the glossopharyngeal and vagus nerves. In the lower two third of the esophagus , the musculature is smooth muscle,here it is strongly controlled by the vagus nerves acting through their connections with the esophageal myenteric nervous system. Even after the paralysis of the swallowing reflex,food fed by tube or in some other way into the lower esophagus still passes readily into stomach,because of the excitement of myenteric plexus of the esophagus which cause initiation of secondary peristalisis .

Function of lower esophageal sphincter:

Function of lower esophageal sphincter At the lower end of the esophagus, the esophageal circular muscle functions as a lower esophageal sphincter which normally remains tonically constricted. When a peristaltic swallowing wave passes down the esophagus,there is a “receptive relaxation” of the lower esophageal sphincter ahead of the peristaltic wave which allows easy propulsion of the swallowed food into the stomach. Rarely the sphincter does not relax satisfactorily resulting in Achalasia The stomach secretions are highly acidic and contain many proteolytic enzymes.the esophageal mucosa,except in the lower eight of the esophagus,is not capable of resisting for long the digestive action of gastric secretions.fortunately the tonic constrictor of the lower esophageal sphincter helps to prevent significant reflux of the stomach contents into the esophagus except under very abnormal conditions

Neural Regulation of Deglutition:

Neural Regulation of Deglutition Pharyngeal Stimulation of receptors 7 th ,9 th and 10 th Cranial Nerves Efferent function 9 th ,10 th Cranial Neves Cricopharyngeal sphincter opening is reflexive. Esophageal Primary Peristalsis Proximal- straited -contracts faster Distal-smooth-contracts last Secondary Peristalsis Intrinsic plexus- Auerbach’s myentric plexus

Cranial Nerves:

Cranial Nerves Cranial Nerves V and XII – chewing and tongue movement. CN VII sensation of the oropharynx and taste to the anterior 2/3 rd of the tongue. CN IX taste sensation to the posterior part of the tongue,sensory and motor function of the pharynx. CN X taste to the oropharynx and sensation and motor function to the larynx and laryngopharynx . Airway protection

Respiration:

Respiration Besides the nose, air can enter into the lungs through the mouth. The pharynx is a tubular structure, positioned behind the oral and nasal cavities, that allows air to pass from the mouth to the lungs. The pharynx contains three parts: The nasopharynx , which connects the upper part of the throat with the nasal cavity; the oropharynx , positioned between the top of the epiglottis and the soft palate; and the laryngopharynx , located below the epiglottis. Air Travel in the Nasopharynx Air that is inhaled from the nose has to make a 90-degree turn in the nasopharynx , which is difficult for large particles in the air. These heavy foreign particles usually travel straight into the back wall of the throat, crashing into and sticking to the pharyngeal tonsil. Air Travel in the Oropharynx As air passes through the oropharynx , the epiglottis remains open. When the epiglottis flaps close, it shuts off the larynx and allows food and drink to pass down the esophagus without causing choking. Passage Linings The nasopharynx takes in only air, and is lined by cells that secrete mucus. This mucus keeps the air we breathe moist and traps any foreign particles, and the mucus is eventually digested by the stomach. The oropharynx and laryngopharynx take in both food and air, and are lined by smooth tissue that resembles our outer skin, only softer. The cells of this tissue, like skin cells, can take a lot of abuse and flake off, which helps food to pass down without injuring the throat.

Muco-Ciliary Clearance :

Muco-Ciliary Clearance The mucous membrane produces secretions which lubricates the pharynx. The passage of airway in the respiratory tract that conducts air into the lungs main bronchi down to the final branchings of the respiratory tree  alveoli are lined with a moist lining of the airway respiratory epithelium. On that, cilia is present,.The cilia are surrounded by a thin fluid film of mucus. On top of that is a second viscous film of mucus, in which foreign particles and microorganisms get stuck. Within the thin fluid film of mucus the cilia act out movements coordinated in direction towards the pharynx. Thereby the viscous film of mucus including its freight is transported off in direction towards the mouth, where it is either swallowed or expelled via coughing.

Voice Resonance :

Voice Resonance The Pharynx is the main resonating chamber for the voice. The resonators include the mouth,the nose and associated nasal sinuses,the pharynx and even the chest cavity. Nasopharynx , nasal cavity & sinuses act as a resonance box. The Eustachian tubes open into the Nasopharynx , making it the path connecting our vocal sound to the ear internally. This area is referred to as the “ ng ” resonator from the sensation of resonance that results from the “ ng ” vocal sound found in words with that spelling, like “sing” and “hung”. It is also referred to as the Head Resonator. Soft palate opens the laryngopharyngeal valve in resonating consonants ( n,m ) & closes it in non-resonating ones. Some consonants are produced at the soft palate region; velar ( Kh,Gh ).

Defence:

Defence Tonsils play an important role in acquiring immunity against infections especially in the first 5 years of life. Tonsils along with other lymphoid tissues in the body also form lymphocytes (WBC). Tonsils also produce Antibodies Ig A. Tonsils produce barrier to infection spread to the body through the Waldeyer’s ring (This is a collection of lymphoid tissue scattered in the pharynx.)

Middle Ear Ventilation:

Middle Ear Ventilation The auditory tube is a trumpet shaped channel which connects the middle ear cavity with the nasopharynx . It aerates the middle ear system and clears mucus from the middle ear into the nasopharynx . Normal opening of the eustachian tube equalizes atmospheric pressure in the middle ear; closing of the eustachian tube protects the middle ear from unwanted pressure fluctuations and loud sounds. Mucociliary clearance drains mucus away from the middle ear into the nasopharynx , thus preventing infection from ascending to the middle ear.

Taste Sensation :

Taste Sensation The Glossopharygeal Nerve (IX)receives general sensory fibers from the tonsils, the pharynx, the middle ear and the posterior 1/3rd of the tongue. Special sensory (special afferent) of the CN IX provides taste sensation from the posterior one-third of the tongue.

Common Diseases associated with Pharynx:

Common Diseases associated with Pharynx Acute Pharyngitis Chronic Pharyngitis Ulceration of the Pharynx Tuberculous Pharynx Dysphagia Esophageal Achalasia Gastroesophageal Reflux Disease

PHYSIOLOGY OF LARYNX:

PHYSIOLOGY OF LARYNX

Functions of Larynx:

Functions of Larynx Protection of the trachebronchial tree Phonation Cough Reflex

Protection of tracheobronchial tree:

Protection of tracheobronchial tree Air passes from the pharynx to the larynx, which is approximately 5 cm (2 inches) long and situated near the middle of the neck. The larynx is comprised of several layers of cartilage, a tough and flexible tissue. In addition to transporting air to the trachea, the larynx serves such other functions as: It prevents food and fluid from entering the air passage which would cause choking. Its mucous membranes and cilia-bearing cells help filter air. It plays a primary role in producing sound. The cilia in the larynx move airborne particles up toward the pharynx to be swallowed.

Cough Reflex:

Cough Reflex During swallowing , the backward motion of the tongue forces the epiglottis over the glottis' opening to prevent swallowed material from entering the larynx which leads to the lungs ; the larynx is also pulled upwards to assist this process. Stimulation of the larynx by ingested matter produces a strong cough reflex to protect the lungs. Cough is a modified respiratory protective mechanism characterized by forced expiration of foreign particles entering the lungs. It is caused by irritation of the larynx,trachea and bronchi,which are very sensitive to touch. An intrusion causes the afferent nerves impulses to pass from the respiratory passage through the vagus nerves to the medulla of the brain. Thus initiates an automatic sequence of events which results in Coughing. About 2.5 liters of air is rapidly inspired.

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The epiglottis closes , and the vocal cords shut tightly to entrap the air within the lungs. The abdominal muscles contracts forcefully,pushing against the diaphragm while the other expiratory muscles such as internal intercostals,also contract forcefully Thus rising the pressure in the lungs The vocal cords and the epiglottis suddenly open widely so that the air under this high pressure in the lungs explodes outwards,causing cough

Phonation :

Phonation The larynx is especially adapted to act as a vibrator. the vibrating element is the vocal folds commonly called the vocal cords. The vocal folds protrude from the laterla walls of the larynx towards the center of the glottis. During normal breathing the folds are wide open to allow easy passage of air. During phonation the folds move together so that passage of air between them will cause vibration. The pitch of the vibration is determines mainly by the degree of stretch of the folds.

Common Diseases associated with larynx:

Common Diseases associated with larynx Acute laryngitis Chronic laryngitis Presbylarynx Ulcers Polyps and nodules cancer of the larynx Vocal cord paresis Laryngopharyngeal reflux Laryngomalacia Laryngeal perichondritis

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