Swallowing

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Physiology lecture

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Mouth and Esophagus:

Mouth and Esophagus Dr Raghuveer Choudhary

Mastication:

Mastication Also called chewing Mastication muscles close the jaws Slide or rock lower jaw from side to side Chewing involves mandible: elevation and depression protraction and retraction medial and lateral movement

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Mastication 1. Mastication is important for the digestions of fruits and raw vegetables. Cellulose membrane 2. Mastication increases the rate of digestion by grinding the food into particles. Total surface area exposed to the digestive juices 3. Mastication prevents excoriation of GI and increase the emptying of food.

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MASTICATION Chewing (mastication) reduces the particle size of food and increases its exposure to saliva. This process lubricates food for swallowing and also aids in carbohydrate digestion by the enzyme salivary amylase. The distribution of foodstuffs around the mouth during chewing stimulates the taste receptors.

Pharynx:

Pharynx Connects nasal and oral cavities with larynx & esophagus Divisions _ nasopharynx , oropharynx , laryngopharynx Superior, middle, inferior PHARYNGEAL CONSTRICTORS – circular – force food down during swallowing

Divisions :

Divisions Nasopharynx - air Most superior to soft palate Oropharynx - Food & air Posterior to mouth Soft palate to esophagus Laryngopharynx - food Esophagus to cricoid cartilage Passageway to esophagus;

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The process of food coming into the stomach from oral cavity . Swallowing 1. Voluntary stage Oral cavity Pharynx 2. Pharyngeal stage Pharynx Esophagus 3. Esophageal stage Stomach Esophagus

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1. Voluntary stage Oral cavity Pharynx The pressure of the tongue upward and backward against the palate.

SWALLOWING :

SWALLOWING Swallowing (deglutition) carries food from the pharynx into the esophagus. There is a voluntary stage when food is shaped into a bolus, collected on the tongue, and pushed into the pharynx. The tongue is then raised against the hard palate to create a pressure gradient that forces the bolus into the pharynx and beyond. When food enters the pharynx, the following involuntary events of the swallowing refl ex occur:

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Once food is forced into the pharynx by the voluntary elevation of the tongue, receptors in the pharynx send messages to the pons and medulla to reflexively cause: The tongue to block the mouth The soft palate to rise The epiglottis to close off the glottis Peristalsis to move the food down the esophagus Relaxation of the cardiac sphincter so that food can enter the stomach. 12

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Tongue block oropharynx Soft palate raised Epiglottis close-off the glottis

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2. Pharyngeal stage Pharynx Esophagus Receptors (pharynx) Trigeminal nerves Brain stem Series of automatic pharyngeal muscle contractions Glossopharyngeal nerves 5 th ,9 th ,10 th ,12 th cranial nerves

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The nasopharynx is closed by the soft palate. ■ Food is prevented from entering the airway by elevation and forward displacement of the larynx and deflection of the food bolus by the epiglottis. ■ The upper esophageal sphincter relaxes to allow the bolus to enter the esophagus.

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1. the trachea is closed 2. the passage between the pharynx and nasal cavities is closed 3. the esophagus is opened 4. a fast peristaltic wave originates in the pharynx and forces the bolus of food into the upper esophagus. 2. Pharyngeal stage Pharynx Esophagus

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The upper esophageal sphincter tone prevents the aspiration of the esophageal contents into the airway. It also prevents the entry of air into the esophagus, since the esophageal body exists at below atmospheric pressure in the thorax.

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The above events are coordinated by a center in the reticular formation, which also inhibits breathing until food is in the esophagus. The oral and pharyngeal component of swallowing is controlled solely by extrinsic nerves. Neurologic damage (e.g., the result of a stroke) can adversely affect this phase of swallowing .

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Swallowing induces a wave of peristalsis in the esophagus known as primary peristalsis. If this wave is insufficient to move a bolus all the way to the stomach, distension of the esophageal wall by a remaining bolus induces secondary peristalsis , which is repeated until the bolus enters the stomach.

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3. Esophageal stage Stomach Esophagus peristalsis primary secondary The continuation of the peristaltic wave that begins in the pharynx and spread into the esophagus Distension of the esophagus Myenteric nervous system esophagus Vagal afferent medulla Vagal efferent Glossopharyngeal nervous

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Oral cavity sphincter stomach Lower esophageal sphincter (gastroesophageal sphincter) Prevents reflux of stomach contents into the esophagus

From Mouth to Stomach (continued):

From Mouth to Stomach (continued) Involuntary muscular contractions and relaxations in the pharynx, and esophagus are coordinated by the swallowing center in the medulla. Esophagus: Connects pharynx to the stomach. Upper third contains skeletal muscle. Middle third contains a mixture of skeletal and smooth muscle. Terminal portion contains only smooth muscle.

The Esophagus:

The Esophagus Figure 24–10

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Gross anatomy Esophageal hiatus Mucosa Muscularis Sphincters ESOPHAGUS upper lower (gastroesophageal) upper esophageal sphincter gastroesophageal sphincter esophagus lumen mucosa submucosa muscularis externa adventitia stratified squamous epithelium IC OL

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ESOPHAGUS The function of the esophagus is to move food and liquid to the stomach and to keep it there.

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The esophagus has three functional zones: 1. The upper zone, which is 6–8 cm long, is closely related to the pharyngeal musculature and consists of striated muscle. 2. The middle zone (main body), which is 12–14 cm long, consists of smooth muscle. 3. The lower zone, which is 3–4 cm long, consists of smooth muscle and corresponds with the lower esophageal sphincter.