Mouth

The mouth starts with the lips in front and extends back to an area called the oropharynx. The oropharynx is where both food and air pass to go into the digestive tube and respiratory tract, respectively. The lips have a circular skeletal muscle called the orbicularis oris, which allows lip movement, as in a pucker or a smile. The skin at the edges of the lips is thin, allowing the natural red coloring of blood to tint the lips. The lips do not have any sweat or sebaceous glands, so they must be moistened on a regular basis or the skin will become dry, crack, and possibly bleed.

The sides of the mouth, or cheeks, contain a skeletal muscle called the buccinator. This muscle helps move food around in the mouth and also helps in forming facial expressions. The inside of each cheek is covered with a stratified squamous epithelium that is not keratinized like skin, so it is not dry, but kept moist by saliva. This type of epithelium was discussed in Chapter 4.

The mouth is bounded on the top by the palate. The top front part of the mouth is called the hard palate and has bone above the tissue lining the mouth. When a person chews and forms certain speech sounds, the tongue presses against the hard palate. The top rear portion of the mouth is called the soft palate and has skeletal muscle, not bone, above the mouth lining. A small finger-like projection of the soft palate at the rear of the mouth is called the uvula. The soft palate raises during swallowing to block the opening to the nasal cavity at the top of the oropharynx, preventing a person from inhaling and swallowing at the same time.

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