Overview
This lecture follows the path of food through the oral cavity, pharynx, and esophagus, highlighting key structures, their functions, and the initial stages of digestion.
Journey of Food: Oral Cavity
- Ingestion is the conscious act of bringing food into the mouth.
- Mastication is the process of mechanically breaking down food using teeth, tongue, and hard palate.
- Saliva and mucus lubricate food, aiding swallowing.
- Salivary amylase in saliva begins digestion of complex carbohydrates in the mouth.
- The oral cavity is lined with non-keratinized stratified squamous epithelium for abrasion resistance.
- The hard palate is bone, while the soft palate (ending in the uvula) is muscular.
- The uvula blocks the nasal cavity during swallowing.
- The tongue shapes food into a bolus and assists swallowing, speech, and taste.
Accessory Structures & Salivary Glands
- Lips are attached to gums via the labial frenulum; gums (gingiva) surround each tooth.
- Three paired major salivary glands: parotid (serous, amylase-rich, 25% of saliva), submandibular (both types, 70%), sublingual (mucous, 5%).
- Two types of saliva: serous (watery, enzyme-rich) and mucous (thick, binding).
Teeth & Tooth Anatomy
- Children have 20 deciduous (baby) teeth; adults normally have 32 permanent teeth.
- Tooth anatomy includes: crown (visible, enamel-coated), neck (at gum line), root (inside gum, anchored by cementum to ligament).
- Enamel (hardest body substance, non-living) covers crown; dentin (bone-like, living tissue) underlies enamel.
- Tooth pulp contains nerves and blood vessels; nerves enter via the root canal.
Swallowing (Deglutition) & Phases
- Swallowing has three phases: buccal (voluntary, tongue pushes bolus to oropharynx), pharyngeal (involuntary, soft palate/uvula block nasopharynx, epiglottis covers larynx), esophageal (peristalsis moves bolus to stomach).
- Upper esophageal sphincter prevents regurgitation; lower sphincter (cardiac sphincter) prevents acid reflux.
Esophagus Structure & Function
- Esophagus is a muscular tube conducting food from pharynx to stomach via peristalsis.
- Lined with non-keratinized stratified squamous epithelium for protection.
- Upper third contains skeletal muscle for swallowing reflex; lower third is smooth muscle for peristalsis.
- Outermost layer is adventitia (fibrous connective tissue) instead of serosa.
Common Disorders
- Gastroesophageal reflux (heartburn) occurs if the lower esophageal sphincter fails, allowing stomach acid upward.
- Hiatal hernia is when the stomach pushes through the diaphragm, worsening reflux risk.
Key Terms & Definitions
- Mastication — chewing, mechanical breakdown of food.
- Bolus — chewed, lubricated mass of food ready to swallow.
- Enamel — hard, non-living outer layer of tooth crown.
- Dentin — bone-like tissue beneath enamel.
- Pulp cavity — center of tooth with nerves and blood vessels.
- Buccal phase — voluntary swallowing stage.
- Peristalsis — muscular contractions moving food down the GI tract.
- Epiglottis — flap covering the larynx during swallowing.
- Adventitia — outer connective tissue layer of the esophagus.
Action Items / Next Steps
- Watch the following lecture on the stomach for further details.
- Review the structure and function of oral and esophageal anatomy.
- Prepare questions for clarification if needed.