Parts of the Digestive System and Their Functions (Part 1)


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 Understanding the parts of the digestive system and their functions can help you understand what can go wrong and how to keep it healthy.

The more I learn about the GI tract (also called the digestive tract, digestive system, or GI system), the more I see how it is the center of our health and healing. This article covers the mouth, esophagus, and stomach. Part 2 covers the small intestine, large intestine, and anus.

Digestion vs. Absorption

Before we start exploring the digestive tract, understanding the difference between digestion and absorption is important.

  • Digestion is when the food you eat and the drinks you drink are broken down into the smallest pieces possible. This happens in steps.
  • Absorption is when those tiny particles that have been digested are absorbed into your body.

Digestive system basic facts

Your digestive system is a long tube inside your body. This tube is about 24 to 30 feet long and starts with your mouth and ends with your anus. The basic parts are:

  • Mouth
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine
  • Rectum
  • Anus

In addition, there are other organs that help the digestive process including the pancreas and gallbladder.

Did you know that your digestive tract is like your skin? It interacts with the outside world constantly. People say that the skin is the largest organ in the body. Actually, I believe, the GI tract is the largest organ in the body if you want to go by surface area.

The GI tract is like a hole through a very long bead. On a necklace, the chain passes through the bead. In your body, all of the food you eat, fluids you drink, and pills you take go in your mouth, get processed and come out the other end.

The processing that happens in your digestive tract means that everything you swallow goes get squished, kneaded, and exposed to acids and digestive enzymes. Then, what your body needs to stay healthy gets extracted, and the waste passed out of your body.

Pretty amazing, right?

Digestion and absorption start in the mouth

Digestion starts in your mouth with your teeth and chewing. Meanwhile, as you chew, your mouth releases saliva which contains digestive enzymes that help break the food into smaller and smaller pieces.

One of the reasons chewing your food thoroughly ]is to break the food into as small pieces as possible. The more pieces – or surface area – there is for the digestive enzymes to work on, the better the rest of your digestion will work.

During the chewing process, some absorption happens in your mouth. Your mouth absorbs some sugars and alcohol.

Your tongue has taste buds all over it. When you were a child, you had more taste buds than you do now. As you age, you lose taste buds. That is why older people need more flavoring in their food.

The esophagus is the path between your mouth and stomach

The esophagus is about 9 ½ inches long. The main purpose of the esophagus is to move food from the mouth to the stomach.

The esophagus is lined with moist, pink tissue called mucosa. Actually, your whole GI tract is lined with it. Mucosa protects the lining of your GI tract while keeping it slippery. This helps keep food moving through your GI tract.

If you have GERD or acid reflux, the acid from your stomach may eat away at the mucosa of the esophagus.

Your GI tract is also lined with muscles just below the surface. These muscles move in a wave-like pattern to help keep the food moving along the digestive tract.

The lower esophageal sphincter separates the esophagus and stomach

At the bottom of the esophagus is the lower esophageal sphincter. The lower esophageal sphincter’s job is to keep the contents of the stomach, including stomach acid, from coming back up into the esophagus.

The esophagus passes through the diaphragm muscle at about the same point as this sphincter. The diaphragm muscle separates your chest and abdomen, or stomach, area.

With GERD or acid reflux, this sphincter that is weakened, or not closing properly, that lets the stomach acid up into the esophagus.

If a hiatal hernia exists, this is where it happens. A small part of the upper stomach will bulge through the opening in the diaphragm.

Digestion and absorption in stomach

An average stomach is about 12 inches long and about 6 inches wide. It holds about 1 quart of food.

The stomach is like a washing machine for food. It tosses the food all around in the stomach fluid which contains hydrochloric acid and digestive enzymes.

The washing machine action continues breaking the food up into smaller and smaller pieces. You want as much of the food exposed to the hydrochloric acid and digestive enzymes as possible because they break the food into teeny, tiny pieces. Those teeny, tiny pieces can ben be absorbed.

Hyrdochloric acid’s role

One of the main components of the fluid in your stomach is a strong acid – hydrochloric acid. This acid is important because it kills bugs, bacteria, and other pathogens that can make us sick. It also helps activate – or make available to our bodies – some vitamins. Hydrochloric acid also helps start the process to break down proteins.

Digestive enzymes in the stomach

In addition to hydrochloric acid, the stomach contains a multitude of digestive enzymes. Each enzyme is specific to the type of food being digested. There are specific enzymes for protein, carbohydrates, and fat.

Absorption in the stomach

While food is being digested, some absorption also happens in the stomach. The following are absorbed in small amounts in the stomach:

  • Alcohol
  • Medications (such as aspirin)
  • Amino acids (the building blocks of proteins)
  • Caffeine
  • Water-soluble vitamins

Stomach ulcers

When the lining of the stomach is damaged, an ulcer can form. H. pylori is a type of bacteria that attacks the stomach lining. Once the lining is damaged, the acid can attack the cells and cause ulcers. Most of us have H. pylori in our digestive tract without it doing any damage. 

Feeling of fullness or sand in the stomach

Sometimes people have a feeling of fullness after taking a few bites or describe that their stomach feels like it has sand in it. Often, this is means that they don’t have enough hydrochloric acid (known as hypochlorhydria) and/or digestive enzymes. (Here’s an article for more information about hypochlorhydria and another about digestive enzymes.)

How long food stays in the stomach

 With all the digestion and absorption going it, your stomach can take about 4 hours to empty. That time depends on how much you ate, how well you chewed it, whether it was liquid or solid, and if it had a lot of fat or protein – they take longer to break down than carbohydrates – among other things.

The pyloric sphincter separates the stomach and the small intestine

At the bottom of the stomach is the pyloric sphincter. The pyloric sphincter controls how fast the stomach empties into the small intestine. This sphincter acts as a one-way door when working properly. This means that food can enter the small intestine through the pyloric sphincter while the contents of the small intestine should not be able to re-enter the stomach.


Gastroparesis is when the digested food does not move through the digestive system properly. One of the things that can happen with gastroparesis is that the stomach doesn’t empty properly. 

To Be Continued

The next part of this article will cover the digestive system from the small intestine to the anus.

If you have an unhappy gut, or if any of these symptoms sound familiar, you can start by looking at the 5 Steps to Restore Digestive Health. Part of the 5 Step program is to remove foods that cause inflammation. Two of those foods are gluten and dairy. If you want to learn more about why you should consider going gluten free and dairy free, you can download my free guide. In addition to information on going gluten free and dairy free, the guide includes easy meal and snack ideas.

This article was originally published on April 28, 2016. It was revised and republished on March 8, 2019.

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4 Responses to "Parts of the Digestive System and Their Functions (Part 1)"
  1. This was great! This gave me some insight into what is really on between inhaling my food (bad habit) and “letting it all go” a few hours later. I loved the ride and can’t wait for part two.

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