The mouth, pharynx, and esophagus work together to start digestion and move food to the stomach. These structures have specialized parts that break down food, form it into a bolus, and push it along the digestive tract.

Swallowing is a complex process involving voluntary and involuntary actions. It ensures food goes down the right path, avoiding the airway. The journey from mouth to stomach involves mechanical and chemical processes, preparing food for further digestion.

Anatomy of the Mouth, Pharynx, and Esophagus

Structures and roles of mouth

• Lips form anterior boundary of mouth prevent food and liquid from spilling out
• Cheeks form lateral boundaries of mouth assist in keeping food between teeth during chewing (buccal mucosa)
• Hard palate forms roof of mouth provides firm surface for tongue to push food against during chewing and swallowing
• Soft palate located posterior to hard palate elevates to prevent food and liquid from entering nasal cavity during swallowing (nasopharynx)
• Tongue muscular organ attached to floor of mouth manipulates food during chewing assists in forming food bolus pushes food bolus into pharynx during swallowing (lingual frenulum)
• Salivary glands include parotid, submandibular, and sublingual glands secrete saliva to moisten food and initiate chemical digestion of carbohydrates (amylase enzyme)

Arrangement of adult teeth

• Adult dentition consists of 32 permanent teeth arranged in specific pattern
• Four types of teeth serve different functions
  1. Incisors anterior teeth with sharp, chisel-shaped crowns function in cutting and biting food (central and lateral incisors)
  2. Canines cone-shaped teeth lateral to incisors function in tearing and gripping food (cuspids)
  3. Premolars posterior to canines function in crushing and grinding food (bicuspids)
  4. Molars posterior to premolars function in crushing and grinding food (first, second, and third molars)
• Dental formula for adult dentition: $2123/2123$ represents number of each tooth type in one-half of upper and lower jaws (quadrants)

Process of swallowing

• Oral phase (voluntary) tongue pushes food bolus against hard palate and into oropharynx
• Pharyngeal phase (involuntary) involves multiple coordinated actions
  • Soft palate elevates to prevent food from entering nasopharynx (velopharyngeal closure)
  • Epiglottis covers larynx to prevent aspiration (epiglottic tilt)
  • Pharyngeal constrictor muscles contract, propelling food bolus into esophagus (pharyngeal peristalsis)
• Esophageal phase (involuntary) begins as food bolus enters esophagus
  • Upper esophageal sphincter relaxes to allow food bolus passage (cricopharyngeus muscle)
  • Peristaltic contractions of esophageal smooth muscle propel food bolus towards stomach (esophageal motility)
  • Lower esophageal sphincter relaxes to allow food bolus to enter stomach (gastroesophageal junction)

Journey from mouth to stomach

• Mouth food is mechanically broken down by chewing (mastication) saliva moistens food and begins carbohydrate digestion tongue forms food into bolus (oral cavity)
• Oropharynx and laryngopharynx food bolus is propelled through pharynx by swallowing reflex epiglottis covers larynx to prevent aspiration (deglutition)
• Esophagus upper esophageal sphincter relaxes to allow food bolus entry peristaltic contractions propel food bolus towards stomach lower esophageal sphincter relaxes, allowing food bolus to enter stomach (gastric filling)

Digestive tract features

• Peristalsis: wave-like muscle contractions that move food through the digestive tract
• Sphincters: circular muscles that control the passage of food between different regions of the digestive system
• Mucosa: innermost layer of the digestive tract, which secretes mucus and enzymes to aid in digestion and protect the tract lining