The oral cavity contains structures for ingestion and fragmentation of food, resulting in formation of a bolus of food for swallowing. The lips, tongue, and palate assist in bringing food into the oral cavity and positioning it during chewing and swallowing. The tongue and lips also participate in speech, and the tongue contains sensory receptors (taste buds) that provide the sensation of taste. The salivary glands secrete saliva containing mucus that moistens food and enzymes that initiate digestion.

• Examine the images below and these sections of lip (sample 1 and sample 2). The skin on the external surface (containing typical features of skin, e.g. hair follicles and sebaceous glands) merges into the nonkeratinized, stratified squamous epithelium of the oral mucosa on the internal surface. Note that the oral epithelium is thicker. Locate the small salivary glands in the submucosa of the lip and the skeletal muscle.

• Examine the diagram below and this section of an adult tooth, which is from a decalcified tooth still embedded in the bone of the jaw. The enamel, a calcified material similar to bone, is completely dissolved away. Identify the following structures:
  
  • Dental pulp
  • Odontoblasts
  • Predentine
  • Dentine
  • Bone
  • Periodontal ligament
  • Cementum
  • Dentine
  • Gingiva

• Examine this section of developing tooth in the lower jaw of the fetal skull. Identify the dental pulp, odontoblasts, dentine, enamel (partially gone), and the (partially disrupted) layer of ameloblasts.

Clinical note: The oral cavity has a large and varied bacterial flora. Bacteria may accumulate and form a layer (plaque) on a tooth, releasing acids that demineralize the enamel and dentine and produce dental cavities. Other bacteria proliferating in the gingival cleft may destroy the periodontal ligament, cause resorption of alveolar bone, and loosening of teeth.
 

Next is the tongue.