Digestive System (Anatomy): How It Works
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Discover the digestive system and understand its intricate processes. From mouth to the intestines, learn about each organ's role in digestion.
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What's the Digestive System?

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 systemâyour gallbladder, liver, and pancreasâand 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.

Digestive System Organs

The human digestive system includes these organs:

Mouth

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.

Throat

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 palateâthe soft part of the roof of your mouthâpush food into the throat, which closes off the windpipe. From here, the food travels to the esophagus or swallowing tube.

Esophagus

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).

Stomach

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 segmentsâthe duodenum, jejunum, and ileumâthe 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.

Rectum

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.

Digestive System Diseases

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