From mouth to stomach
From Mouth to Stomach
When you chew food, you actually break it down with your teeth. Tongue movements help mix the food with saliva, forming it into a soft lump called a bolus.
Saliva in your mouth contains water and enzymes, which are secreted by the salivary glands. Enzymes are molecules that speed up chemical reactions. Some enzymes break down food very rapidly — for example, one type of enzyme in saliva helps digest starch into simple sugars.
Common Mistake
Saliva is not just water — it contains important enzymes like amylase that begin the digestion of carbohydrates in the mouth.
Why Sugar Can Cause Tooth Decay
You may have heard that eating sugary foods and sweets is one of the causes of tooth decay. But why?
Some foods contain substances that serve as food for bacteria in the mouth. These bacteria produce acid. The acid erodes tooth enamel and eventually causes cavities.
Important Concept
Tooth enamel is the hard outer layer of a tooth. Once it's eroded by acid, it cannot regenerate — making tooth decay permanent unless treated.
Question
Show Answer
a) The shape of each tooth matches its function. Incisors have sharp edges for cutting food. Canines are pointed for tearing food. Molars are broad and flat, suited for grinding and chewing.
b) Adults usually have 8 incisors, 4 canines, 8 premolars (small molars), and 12 molars (including wisdom teeth).
Swallowing and the Role of the Pharynx
After you chew food and swallow it, nothing resembling a food lump is left. The next stop is the esophagus. The lump of food is soft and moist, formed before entering the esophagus. It sits at the top of the throat, in an area called the pharynx.
When you swallow, only one path opens — the others are closed — so the lump of food can only move in one direction. That’s why the chewed food enters the esophagus and not the airways.
Question
Using the diagram, explain why this happens.
Show Answer
This happens when the epiglottis fails to fully close the windpipe (trachea) during swallowing, allowing food or drink to enter the airway. This triggers a strong coughing reflex to clear the airway and protect the lungs.
From Esophagus to Stomach
When food enters the esophagus, the muscles in the esophageal wall contract and relax in a wave-like pattern. As a result, the food is pushed downward toward the stomach.
Food remains in the stomach long enough to be thoroughly mixed with digestive juices. These digestive juices contain enzymes and acid. These substances help break down food.
When the stomach wall muscles contract, the food is churned and combined with the digestive juice. The digested food becomes thinner and enters the small intestine.
Example
The squeezing motion that pushes food through the esophagus is called peristalsis. It continues throughout the digestive tract, including in the intestines.
Question
Show Answer
Food moves through the esophagus by muscular contractions called peristalsis, not by gravity. This rhythmic squeezing pushes food toward the stomach even if you are upside down.