The Mouth and Pharynx - ions in saliva neutralize the acids...

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The Mouth and Pharynx Mechanical breakdown begins in the mouth by chewing (teeth) and actions of the tongue. Chemical breakdown of starch by production of salivary amylase from the salivary glands . This mixture of food and saliva is then pushed into the pharynx and esophagus . The esophagus is a muscular tube whose muscular contractions ( peristalsis ) propel food to the stomach. In the mouth, teeth, jaws and the tongue begin the mechanical breakdown of food into smaller particles, as shown in Figure 3. Most vertebrates, except birds (who have lost their teeth to a hardened bill), have teeth for tearing, grinding and chewing food. The tongue manipulates food during chewing and swallowing; mammals have tastebuds clustered on their tongues. Salivary glands secrete salivary amylase, an enzyme that begins the breakdown of starch into glucose. Mucus moistens food and lubricates the esophagus. Bicarbonate
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Unformatted text preview: ions in saliva neutralize the acids in foods. Swallowing moves food from the mouth through the pharynx into the esophagus and then to the stomach. • Step 1: A mass of chewed, moistened food, a bolus, is moved to the back of the moth by the tongue. In the pharynx, the bolus triggers an involuntary swallowing reflex that prevents food from entering the lungs, and directs the bolus into the esophagus. • Step 2: Muscles in the esophagus propel the bolus by waves of involuntary muscular contractions (peristalsis) of smooth muscle lining the esophagus. Peristalsis is shown in Figure 4. • Step 3: The bolus passes through the gastroesophogeal sphincter, into the stomach. Heartburn results from irritation of the esophagus by gastric juices that leak through this sphincter. •...
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The Mouth and Pharynx - ions in saliva neutralize the acids...

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