The Digestive System: Functions & Physiological Processes

Instructor: Christopher Sailus

Chris has an M.A. in history and taught university and high school history.

In this lesson, we explore the functions and processes of the digestive system, where the food we eat is broken down and turned into the energy we use to do virtually everything else. A short quiz follows.

A First Glance at the Digestive System

Everyone likes food. Sure, people have their preferences--some people only eat fruit and vegetables, while others eat more meat than they should! In the end, though, it all goes to the same place.

In this lesson, we will explore the digestive system and learn exactly where that food goes, as well as the processes it undergoes, in order to be turned into the energy we all need to walk, run, think, and eat more.


Mouths are not just for tasting the delicious food we stuff into them; they also serve as an important part of our digestive system. After all, have you tried to swallow an entire watermelon? Exactly. The chewing and manipulation of food we do with our teeth and tongue help break it down into smaller and more manageable chunks.

The tongue is also where our taste buds are located. Our taste buds have been modified over millennia to help us differentiate food that is good or bad for us. For example, have you ever drank sour milk? Tasted bad, didn't it? That's because it had curdled and likely contained bacteria that can be harmful to humans. The bad taste you got when you tried to drink it was your body warning you that you probably shouldn't swallow it.

In addition, saliva plays an important role in beginning digestion by breaking down food and making it softer until it forms into a bolus--a fancy word for a mound of food that is soft and small enough to be easily swallowed. Saliva also contains enzymes that begin the digestive process and help keep the teeth and tongue clean.


Once food is swallowed, it travels down the pharynx (throat) and into the esophagus. Both serve largely as a passageway for food from the mouth to the stomach. They are lined with specialized muscles that help massage and move food downward.

The esophagus performs some other important functions; for instance, a specialized flap of skin in the esophagus, the upper sphincter, helps ensure that food goes into the stomach and not into the trachea and lungs. After all, food does not belong in the lungs; anyone who has gone into a coughing fit after accidentally aspirating some water knows this!

The lower sphincter of the esophagus serves as the passageway for food from the throat into the stomach and acts as an important barrier, preventing the contents of the stomach from spilling back up into the throat. Acid can more easily bypass this barrier than regular food, and when it does, it causes heartburn.


The stomach is where the food really begins to be broken down. In the main part of the stomach, highly corrosive acids and various types of enzymes break down food into its constituent parts and begin to separate the useful bits from the not so useful bits.

After the food has been broken down and separated in the stomach, the constituent parts are sent to other organs. For example, the liver performs important duties like breaking down various sugars and cleaning some toxins out of the body. The liver also produces bile that aids in the absorption and breaking down of various enzymes in other bodily organs. Bile is stored in the gallbladder. The pancreas also provides an important function in the digestive system--regulating blood sugar. When we eat something that has too much sugar in it, like a candy bar or a piece of cake, our pancreas releases insulin to try to counteract the sugar's effects on our system.

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