The Digestive System: How It Works

Medically Reviewed by Poonam Sachdev on December 05, 2023
7 min read

Your digestive system is a group of connected organs that work together to turn the food you eat into nutrients your body needs to function. It includes your biliary system—your gallbladder, liver, and pancreas—and your digestive tract.

What is the digestive tract?

The digestive tract (or gastrointestinal [GI] tract) is a long, twisting tube that starts at the mouth and ends at the anus. It's made up of a series of hollow organs that coordinate the movement of food and waste.

Along the way are the solid organs that make up your biliary system, which produces enzymes and hormones that aid in the breakdown of food.

Everything above the large intestine is called the upper GI tract. The large intestine and everything below it is the lower GI tract.

Digestion is the complicated process of turning the food you eat into nutrients, which your body uses for energy, growth, and cell repair. The digestion process also involves creating waste to be eliminated from your body.

Digestive system process

With the help of hormones and nerves, your digestive system processes the food you take in. The muscles within your organs push it along as your digestive system breaks nutrients—carbohydrates, fats, protein, vitamin, minerals, and liquid—into pieces small enough for your body to absorb. Then your body moves the nutrients where they're needed. The waste products that are left over become poop.

The human digestive system includes these organs:


The mouth is the beginning of the digestive tract. In fact, digestion starts here before you even take the first bite of a meal. The smell of food triggers your salivary glands, making your mouth water. When you actually taste the food, saliva increases.

Once you start chewing, other processes come into play. More saliva is produced. It contains substances, including enzymes, that start the process of breaking down food.


Also called the pharynx, the throat is the next destination for the food you've eaten. Branching off the throat is the esophagus, which carries food to your stomach, and the trachea or windpipe, which carries air to your lungs.

Swallowing takes place in the throat, partly as a reflex and partly under your control. The tongue and soft palate—the soft part of the roof of your mouth—push food into the throat, which closes off the windpipe. From here, the food travels to the esophagus or swallowing tube.


The esophagus is a muscular tube that goes from the throat, behind the windpipe, and to the stomach. Food gets pushed through the esophagus and into the stomach by a series of muscle contractions, called peristalsis.

Just before the connection to the stomach, there's an important ring-shaped muscle called the lower esophageal sphincter (LES). This sphincter opens to let food pass into your stomach and closes to keep it there. If your LES doesn't work properly, you may have a condition called gastroesophageal reflux disease (GERD), or reflux, which causes heartburn and regurgitation (the feeling of food coming back up).


The stomach is a sac-like organ with strong muscular walls. It serves as a mixer and grinder of food. It puts out acid and powerful enzymes that continue the process of breaking down the food and changing it to a consistency of liquid or paste.

Parts of the food that can't be liquified are released from the stomach and ushered through the intestines to be eliminated.

Small intestine

Made up of three segments—the duodenum, jejunum, and ileum—the small intestine is the workhorse of digestion. This is where most nutrients are absorbed. It's a long tube loosely coiled in your abdomen (spread out, it would be more than 20 feet long).

Peristalsis is also at work here, moving food through and mixing it with enzymes from the pancreas and bile from the liver. The duodenum is largely responsible for the continuing breakdown of food. The jejunum and ileum are mainly responsible for the absorption of nutrients into your bloodstream.

A more technical name for this part of the process is "motility" because it involves moving or emptying food particles from one part to the next. It's controlled by a large network of nerves, hormones, and muscles. Problems with any of these parts can cause a variety of health conditions.

After nutrients are absorbed through the walls of your small intestine, the waste that's leftover moves into your colon.

Colon (large intestine)

The colon, or large intestine, is a 5- to 7-feet-long muscular tube linking your small intestine to your rectum. This very specialized organ processes waste so you can eliminate it as poop.

It's made up of these parts:

  • Cecum, the uppermost section

  • Ascending (right) colon, which connects to the appendix

  • Transverse (across) colon

  • Descending (left) colon

  • Sigmoid colon, the S-shaped section that connects to the rectum

  • Peristalsis pushes waste left over from the digestion process through the colon. The colon absorbs more water, and the waste ends up in solid form as poop. When the lower colon gets full of poop, it empties into the rectum. It usually takes about 36 hours for waste to get through the colon.


The rectum is the 8-inch long section at the bottom of your colon. When it fills with poop, its walls get stretched, signaling your brain that you need to go to the bathroom. If that's not convenient at the moment, the rectum stores the poop until you can go.

The rectum also puts out mucus that helps the poop pass more easily.


The endpoint of your digestive tract is the anus, the opening where poop leaves your body. It's lined with muscles that help you control when you poop. A ring of muscle called the anal sphincter keeps the opening closed until you're ready to go.

The organs that make up the biliary system play an essential role in helping your stomach and small intestine digest food:

  • Pancreas. Among other functions, the pancreas discharges enzymes into the small intestine that work to break down protein, fat, and carbohydrates from the food we eat. It also makes insulin, a hormone that helps you digest sugars.
  • Liver. The liver has many jobs. Two of its main ones in the digestive system are to make bilea compound that helps you digest fat—and to process nutrients absorbed by the small intestine so your body can use them.
  • Gallbladder. The gallbladder is a storage sac for excess bile. Bile made in the liver travels to the small intestine via the bile ducts. If the intestine doesn't need it, the bile travels to the gallbladder, where it awaits the signal from the intestines that food is present.

Because digestive system anatomy and functions are so complicated, many health conditions can affect it. They range from short-term, minor issues to long-lasting (chronic) diseases.

From time to time, most people will have digestive problems like:

  • Constipation
  • Diarrhea
  • Heartburn
  • "Stomach flu" or gastroenteritis
  • Hemorrhoids

But if you often have digestive symptoms, let your doctor know. It could be a sign of something more serious such as:

  • Irritable bowel syndrome, a problem with your colon that causes uncomfortable symptoms like gas, cramps, and changes in your bowel movements
  • Inflammatory bowel disease like Crohn's disease and ulcerative colitis, which causes widespread irritation in your digestive tract lining
  • GERD, where acid from your stomach often goes the wrong way up your esophagus
  • Celiac disease, in which your body has a serious autoimmune reaction to gluten, a protein in barley, rye, and wheat
  • Diverticulitis and diverticulosis, two conditions in which pockets bulge out from the lining of your colon
  • Cancers of digestive organs, such as the colon, esophagus, liver, pancreas, or stomach

Your digestive system consists of a series of linked organs, stretching from your mouth to your anus. Together, they work to turn food you eat into nutrients your body needs for energy, growth, and cell repair. Your digestive system also helps your body eliminate the waste products that are left over after this process.

What are the four main functions of the digestive system?

The main jobs of your digestive system are:

  • Taking in and digesting food
  • Absorbing nutrients from the food
  • Releasing enzymes and liquid to help digestion
  • Eliminating waste

How long is your large intestine?

Your large intestine is around 5 feet long. It's shorter and wider than your small intestine and takes a much direct path through your body.

How do you keep your digestive system healthy?

Some things you can do to keep your digestive system working its best include:

  • Follow a well-balanced diet that limits saturated fats and processed foods. Include plenty of fruits, veggies, and whole grains, which are rich in fiber and help keep you regular.
  • Exercise regularly. Moving your body helps keep food moving through your digestive system. Try taking a walk each evening after dinner.
  • Drink enough fluids. Dehydration can lead to constipation.
  • Chew your food well. It kick-starts the digestive process by starting to break down your food into smaller pieces and helps you make plenty of saliva.
  • Stop smoking and limit alcohol. These habits contribute to digestive issues like reflux, ulcers, and heartburn.