Mouth, teeth and swallowing

Your salivary glands make about 1 to 1.5 litres of saliva a day, and 99.4% of it is water.

Teeth and tongue

Digestion starts before the first swallow. The teeth and tongue begin mechanical digestion, and the salivary glands begin chemical digestion. Your first set of teeth, the 20 deciduous or baby teeth, begin to appear at about 6 months of age. Baby teeth are gradually replaced from about age 6. The full adult set can include 32 teeth, with wisdom teeth often appearing later. Incisors at the front cut, canines tear, and premolars and molars crush and grind. The third molar in each set is commonly called a wisdom tooth because it often does not appear until early adulthood.

OpenStax calls the tongue a workhorse. It moves food around for chewing, pushes it into a ball, senses taste, texture and temperature, helps you swallow and shapes the sounds of speech. Glands in the tongue also release lingual lipase, an enzyme for fats, although it does not start working until it reaches the acid of the stomach.

Saliva

Three pairs of major salivary glands empty into the mouth. The parotid glands, in front of the ears, make a watery saliva that contains salivary amylase. The submandibular glands under the jaw make saliva with both amylase and mucus. The sublingual glands under the tongue make the thickest saliva with the least amylase. Saliva moistens food so that it forms a soft lump called a bolus and slides down easily. Its amylase starts breaking starch into sugars, and it keeps working in the swallowed food until stomach acid stops it.

The NIDDK adds a detail you have probably noticed. When you see or smell food, your brain sends a signal that makes your salivary glands start working before you take a bite: your mouth waters.

Swallowing without choking

Swallowing has to send food into one tube while keeping it out of another, because the throat is shared by food and air. It starts as a voluntary act: the tongue presses up and back against the palate and pushes the bolus into the throat. From there it becomes automatic. The soft palate and the uvula rise to close off the passage to the nose. The larynx is pulled upward and a flap of cartilage, the epiglottis, folds down over its opening so that food does not enter the windpipe. Muscles in the throat then squeeze the bolus into the esophagus.

The esophagus is a muscular tube about 25.4 cm (10 inches) long that lies behind the windpipe and stays flat when it is empty. Waves of peristalsis carry the bolus down, while glands in its wall add mucus to reduce friction. At the bottom a ring of muscle, the lower esophageal sphincter, relaxes to let food into the stomach. Most of the time it stays closed, which keeps the stomach's contents from flowing back up.

This is educational material about how the body is built and works. It is not medical advice and is not for diagnosing or treating anyone.