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Medicine LibreTexts

22.4A: Mouth

LEARNING OBJECTIVES

  • Describe the features of the mouth that play a role in digestion

The mouth has a variety of roles in human anatomy and sociology. While its primary function is to begin the process of mechanically and chemically digesting food, the mouth is also the beginning of the alimentary canal—a larger digestive tube. Without the human mouth, expressions of the lips and language of the tongue and throat would be impossible.

The mouth is the first portion of the alimentary canal. It receives food and moistens the food with saliva, while the food is mechanically processed (mastication) by the teeth. The mouth is also known as the oral cavity, and within the oral cavity sits the tongue, the soft and hard palate, the uvula, and numerous salivary glands.

The oral mucosa is the mucous membrane epithelial tissue that lines the inside of the mouth. This membrane maintains a moist and lubricated environment within the mouth to prepare the digestive system for the entry of food.

The Mouth as a Communication and Breathing Tool

This is an illustration of the inside of a human mouth. The cheeks have been omitted in the drawing and the lips pulled back for an unobstructed view of the teeth, tongue, jaw bones, uvula, and alimentary canal.

Inside of the mouth: An illustration of the inside of a human mouth. The cheeks have been omitted in the drawing and the lips pulled back for an unobstructed view of the teeth, tongue, jaw bones, uvula, and alimentary canal.

In addition to its primary function as the beginning of the digestive system, the mouth also plays a significant role in human communication and breathing. The primary features of human voice are produced in the throat, but the tongue, lips, and jaw also work together to produce the range of sounds we see in human language.

Air is drawn in through the mouth to the trachea and lungs, and the lips and tongue form words. The lips mark the transition from the mucous membrane to the outer  epithelial skin that covers most of the body. Lips are remarkably sensitive and often serve as an infant’s second hands with which to explore the world.

Mechanical Food Breakdown by Teeth

In the digestive process, the mouth’s purpose is to prepare food for further digestion in the stomach and the small intestine. This process begins with the mechanical breakdown of food by the teeth, which fit into the alveolar arches. The front teeth (incisors and canines) are used to cut and tear food, while the teeth further back (bicuspids and molars) crush and grind.

Food Lubrication and Chemical Digestion By Saliva

Saliva is projected from three main pairs of salivary glands: the large parotid glands near the cheeks, the submandibular glands beneath the mandible, and the sublingual glands beneath the tongue.

Saliva keeps the mouth moist and lubricates the food, helping the tongue form the food into a soft wad, called a bolus. The fluid of saliva also contains several enzymes, notably lysozyme—an antibacterial agent—and amylase, which catalyzes large starch molecules into simpler sugars via hydrolysis.

This is a cross-section drawing of the head and neck in mid-sagittal view. It shows the structures of the mouth and throat. The lips, jaw, nasal cavity, palate, tongue, oral cavity, pharyhnix, epiglotis, larynx opening into pharynx, larynx, and esophagus are labeled.

Cross section of the head and neck: A cross section of the head and neck in mid-sagittal view, showing the structures of the mouth and throat.

Once properly chewed and lubricated, food and drink are swallowed into the esophagus, the tube that leads to the stomach.

The Structures of the Lips and External Mouth

Infant humans are born with an instinctual sucking reflex, by which they know how to gain nourishment using their lips and jaw. The philtrum, or bow of the lip, is the vertical groove or dip just below the nose. The nasolabial folds are the deep creases of tissue that extend from the nose to the sides of the mouth. One of the first signs of age on the human face is the increase in prominence of the nasolabial folds.

Key Points

  • The mouth is also known as the oral cavity. Its purpose is to mechanically break down food, moisten it with saliva, and swallow the food into the esophagus and the stomach.
  • While vocal sounds are primarily produced in the throat, the tongue, lips, and jaw are also needed to produce the range of sounds included in human language.
  • Saliva is produced by three main pairs of salivary glands: the parotid, the submandibular, and sublingual. When food is chewed and mixed with this saliva, the resulting wad is known as a bolus.

Key Terms

  • mastication: The process of physical and mechanical breakdown of food; chewing.
  • mucous membrane: A membrane that secretes mucus. It forms the lining of various body passages that communicate with the air, such as the respiratory, genitourinary, and alimentary tracts.
  • mouth: The opening of a organism through which food is ingested.
  • saliva: A clear, slightly alkaline liquid secreted into the mouth by the salivary glands and mucous glands that consists of water, mucin, protein, and enzymes. It moistens the mouth, lubricates ingested food, and begins the breakdown of starches.
  • uvula: A soft, punching-bag-like piece of tissue that hangs at the back of the mouth and functions in closing the air passages during swallowing, in conjunction with the epiglottis of the trachea.
  • hard palate: The bony roof of the mouth, located ventrally to the soft palate.
  • alimentary canal: The organs of a human or a non-human animal through which food passes.
  • alveolar arch: The part of the upper or lower jawbones in which the teeth are set.