Structures of the Oral Cavity Are Responsible for the First Step of Digestion: Ingestion

Profile view of the oral cavity showing the teeth, tongue, hard and soft palatesThe oral cavity is bounded by the teeth, tongue, hard palate, and soft palate. These structures make up the mouth and play a key role in the first step of digestion: ingestion. This is where the teeth and tongue work with salivary glands to break down food into small masses that can be swallowed, preparing them for the journey through the alimentary canal.

1. Mechanical Digestion Begins When the Teeth Break Down Ingested Food

Click to play animated description of chewing

The movement of the jaw enables the teeth to grind food into small fragments. The mandible, or jawbone, is the only bone in the head that moves, and the points where the temporal bones connect to the mandible make up the only two movable joints in the head. The official name for chewing is mastication. This is the first step in mechanical digestion.

2. Saliva Moistens Food and Begins the Process of Chemical Digestion

Salivary glands of the mouth to aid digestionSaliva secreted by salivary glands aids the mechanical and chemical process of digestion. Saliva is about 99% water and not only moistens food but cleanses the mouth, dissolves food chemicals so they can be tasted, and contains enzymes that start the chemical breakdown of starchy foods. There are three pairs of salivary glands: parotid, sublingual, and submandibular (also called the submaxillary gland).

3. The Tongue Creates a Bolus so It Can Travel Down the Pharynx and Esophagus

Click for an animated depiction of peristalsis

The tongue manipulates the chewed food into a small mass called a bolus, then moves it to the oropharynx. The next steps are involuntary: the bolus passes through the pharynx, the epiglottis closes off the trachea and directs the bolus down the esophagus, and peristaltic waves move the bolus into the stomach.

 

External Resources

A description of the oral cavity from the 1918 edition of Gray's Anatomy of the Human Body.

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