CHAPTER 24 Digestive System

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ASSESS YOUR PROGRESS

12. Where are the visceral peritoneumperitoneum found? Defineretroperitoneal organs.

13. What is the function of the 14. What are the mesenteries?location of the mesenteries

Upper lip (labium)

Labial frenulum of upper lip

Vestibule (superior)

Gingiva covering themaxillary alveolarprocess

Hard palate

Soft palate

24.6 Oral Cavity

LEARNING OUTCOMES

Fauces

Uvula

Cheek

Tongue

Lingual frenulum

Molars

Openings of thesubmandibular ducts

Premolars

Gingiva covering themandibular alveolarprocess

Labial frenulumof lower lip Lower lip (labium)

Anterior view

Incisors

After reading this section, you

A. Describe the oral cavity andof the lips, cheeks, palate, B. Outline the structure anddescribe the process of mastication. C. Compare the structures andsalivary glands and describefunctions of saliva and the

The oral cavity (figure 24.6),regions: (1) The vestibule (ves′ti-bool;the lips or cheeks and the teeth,medial to the teeth. The oral cavitysquamous epithelium, which protects

Lips, Cheeks, and Palate

The lips, or labia (l ā ′b ē - ă ; figure 24.6), are muscular structuresformed mostly by the orbicularis oris ( ō r-bik′ ū -l ā ′ris ō r′is) muscle (see figure 10.9) and connective tissue. The outer surfaces of the lipsare covered by skin. The keratinized stratified epithelium of the skinis thin at the margin of the lips and is not as highly keratinized as theepithelium of the surrounding skin (see chapter 5); consequently, itis more transparent than the epithelium over the rest of the body. Thecolor from the underlying blood vessels shows through the relativelytransparent epithelium, giving the lips a reddish-pink to dark redappearance, depending on the overlying pigment. At the internalmargin of the lips, the epithelium is continuous with the moist strati-fied squamous epithelium of the mucosa in the oral cavity.One or more labial frenula (fren′ ū -l ă ; sing. frenulum ), whichare mucosal folds, extend from the alveolar process of the maxillato the upper lip and from the alveolar process of the mandible tothe lower lip.The cheeks form the lateral walls of the oral cavity. Theyconsist of an interior lining of moist stratified squamous epithe-lium and an exterior covering of skin. The substance of the cheekincludes the buccinator muscle (see chapter 10), which flattensthe cheek against the teeth, and the buccal fat pad, which roundsout the profile on the side of the face.The lips and cheeks are important in mastication and speech.They help manipulate food within the oral cavity and hold it inplace while the teeth crush or tear it. They also help form wordswhen we speak. A large number of the muscles of facial expres-sion are involved in moving the cheeks and lips (see chapter 10).

FIGURE 24.6 Oral Cavity

The roof of the oral cavity is called the palate. The palate sepa-rates the oral and nasal cavities and prevents food from passing intothe nasal cavity during chewing and swallowing. The palate consistsof two parts (figure 24.6). The anterior, bony part is the hard palate (see chapter 7). The posterior, nonbony part is the soft palate, which consists of skeletal muscle and connective tissue. The uvula ( ū ′v ū -l ă ; a grape) is a posterior projection from the soft palate. Theposterior boundary of the oral cavity is the fauces (faw′s ē z), whichis the opening into the pharynx, or throat . The palatine tonsils arein the lateral wall of the fauces (see chapter 22).

Tongue

The tongue is a large, muscular organ that occupies most of the oralcavity proper when the mouth is closed. Its major attachment in theoral cavity is through its posterior part. The anterior part of thetongue is relatively free, except for attachment to the floor of themouth by a thin fold of tissue called the lingual (tongue) frenulum. The muscles associated with the tongue are divided into two catego-ries: Intrinsic muscles are within the tongue itself, and extrinsicmuscles are outside the tongue but attached to it. The intrinsicmuscles are largely responsible for changing the shape of the tongue,