Mouth

Mouth

Digestion begins in the mouth, which is also known as the oral cavity or buccal cavity. It is encompassed superiorly by the palate, anteriorly by the lips, laterally by the cheeks, and inferiorly by the tongue. The oral orifice consists of the mouth’s anterior opening. The mouth is continuous posteriorly with the oropharynx. Solid particles of food are reduced mechanically and mixed with saliva. The vestibule is the portion that lies between the teeth, cheeks, and lips.

Tongue

The tongue is covered by a mucous membrane and is connected to the floor of the mouth by a membranous fold called the lingual frenulum. The body of the tongue is made up of primarily interlaced, bundled skel-etal muscle. It mixes food particles with saliva during chewing, moving food, in the form of a mass called a bolus, toward the pharynx during swallowing. The tongue also moves food underneath the teeth for chew-ing and helps to form consonant sounds when speaking.

The tongue contains intrinsic and extrinsic skele-tal muscle fibers. Its intrinsic muscles are within the tongue itself and not attached to any bones. However, its extrinsic muscles originate on either the skull bones or soft palate, extending to the tongue. They change the tongue’s position and are able to move it left and right and cause it to protrude or retract. There is a median septum of connective tissues, with each half containing identical muscle groups.

The tongue has rough papillae that project from its surface to provide friction (FIGURE 24-5). These ­peg-like projections emerge from the mucosa.The filiform­ papillae are cone-shaped and make the tongue’s surface rougher. They aid in eating semisolid foods, providing friction so these foods can be manip-ulated. They are found in parallel rows on the dorsum of the tongue and are the smallest, most numerous type of papillae. Keratin is contained within the fili-form papillae, causing the tongue to have a somewhat white appearance. The keratin makes the filiform papillae stiff in comparison with other papillae.

Over much of the tongue’s surface are scattered fungiform papillae, which are mushroom shaped. They have a red appearance because of their vascular cores. In a V-shaped row on the posterior tongue are 10–12 vallate papillae. These papillae are very large, appear similar to the fungiform papillae, and have a furrow that surrounds them. On the lateral aspects of the posterior tongue are found foliate papillae, which appear as if they are folded into “pleats.” The fungiform, vallate, and foliate papillae also contain the taste buds. In infancy and early childhood, the taste buds of the foliate papillae are most functional, with reduced function later in life. There are no papillae on the mucosa that covers the root of the tongue.

Tonsils and Palate

The root of the tongue is connected to the hyoid bone and covered with rounded lymphatic tissue masses called lingual tonsils, giving it a bumpy texture. The lingual tonsils lie just deep to the mucosa. The roof of the oral cavity is formed by the palate, which consists of a bony, anterior hard palate and a muscular, posterior soft palate. The soft palate arches posteriorly and down-ward into a cone-shaped projection called the uvula. In the back of the mouth, on either side of the tongue and near the palate, are masses of lymphatic tissue called the palatine tonsils. They lie beneath the epithelial lining of the mouth and help to protect against infection.

The pharyngeal arches lie on either side of the uvula, and the more anterior palatoglossal arch is located between the soft palate and the base of the tongue. The fauces is the arched opening between the soft palate and base of the tongue and is formed by a curved line connecting the palatoglossal arches and uvula. The fauces create the passage between the oral cavity and oropharynx. Extending from the soft palate to the pharyngeal wall is the more posterior palatopharyngeal arch. One palatine tonsil lies between the palatoglossal and palatopharyngeal arches on either side.

The pharyngeal tonsils are also known as the adenoids. They lie on the posterior pharynx, above the border of the soft palate. When the adenoids enlarge to block the passage between the nasal cavity and pharynx, they may be surgically removed, similar to the palatine tonsils.

1. Describe the structures that encompass the oral cavity.

2. Explain the various functions of the tongue.

3. Differentiate between the various types of tonsils.

4. Describe foliate and vallate papillae.