6 Mouth, Tongue, Oral Cavity

The Mouth and Oral Cavity:

Understandably, digestion starts in the mouth and quickly progresses into the hollow space in the mouth known as the oral cavity. Teeth begin mechanical digestion through tearing and crushing of foodstuffs. The mouth is also the site of chemical digestion as saliva helps break down food using enzymes. The mouth houses several pairs of salivary glands as depicted in the figure below:

• The first of the three major salivary glands is the parotid glands located inferior and anterior to the ears.
• The submandibular glands are within the floor of the mouth.
• The sublingual glands lie beneath the tongue.

Salivary Gland Contents:

Each gland produces saliva which is 99.5% water and 0.5% solutes including several ions, dissolved gasses and various inorganic substances. However, there are several enzymes like salivary amylase (which breaks down polysaccharides), lingual lipase (which becomes active in the stomach to process dietary triglycerides) and bacteriolytic lysozymes.

Pharynx:

Food that is swallowed will enter the pharynx, a muscular funnel shaped structure behind the oral cavity extending towards the larynx and esophagus as a bolus of food. The pharynx has 3 distinct regions ranging superiorly to inferiorly:

• Nasopharynx: allows passage of air to the throat
• Oropharynx: allows passage of air and food through
• Laryngopharynx: directs food towards the esophagus and air towards the larynx