How Does the Digestive System Work?



When swallowed food and beverages enter your stomach, your stomach muscles mix them with digestive juices — containing stomach acid and enzymes — that are produced by glands in your stomach lining, the NIDDK


Once your stomach contents are mixed thoroughly, a small amount, called chyme, passes through a valve called the pylorus, into the upper section of your small intestine (known as the duodenum) at regular intervals, cites a review.

A number of problems related to digestion can happen in your stomach. Indigestion (dyspepsia), discomfort or pain in your upper stomach, can occur due to overeating, consuming spicy or greasy foods or alcohol or caffeine, smoking, or anxiety, the Mayo Clinic

notes. Gastritis — inflammation in the stomach lining — can happen when your immune system reacts to an infection, stress, certain medications, or something foreign in the stomach, according to the Cleveland Clinic.

Gastroparesis, or delayed stomach emptying, happens when muscle contractions in your stomach are weaker and slower

than they should be. The cause isn’t always known, but it is often related to nerve damage caused by elevated blood sugar in people with diabetes.


Located behind the stomach, the pancreas produces enzymes that help digest carbohydrates, proteins, and fats. It also plays a role in controlling the amount of sugar (glucose) in your bloodstream by producing hormones such as insulin and glucagon. Pancreatitis, or inflammation of the pancreas, is a painful condition that can occur when enzymes build up in the organ and begin to digest the organ itself, notes Columbia University Irving Medical Center.

And if your pancreas doesn’t make enough enzymes or they don’t reach your small intestine or mix with your food properly, your digestion can suffer from what is known as exocrine pancreatic insufficiency, according to the NIDDK.


Your liver is located in the upper-right portion of your abdomen. The organ produces bile, which is stored in your gallbladder and helps digest fats by breaking them down into smaller pieces (known as fatty acids). When fatty substances from food enter your small intestine, your gallbladder releases bile through bile ducts into the small intestine, the Cleveland Clinic

notes. Your liver also helps control the amount of sugar (glucose) in your blood by storing and releasing glucose as needed.

Small Intestine

Your small intestine uses digestive juices from the pancreas and liver to digest your food and extract nutrients.

Most nutrients and up to 90 percent of the water you consume is absorbed in the small intestine, according to StatPearls.

Special cells in your small intestine help nutrients pass through the intestinal lining into your bloodstream.

Your small intestine is the longest part of your digestive system — about 20 feet long, according to the National Library of Medicine

— and a number of problems can develop in this organ, from infections and bleeding to obstruction — a partial or complete blockage,

which can occur as a result of scar tissue from surgery or due to certain diseases (including Crohn’s disease and cancer). You can also experience problems with absorbing nutrients — known as malabsorption — which can be caused by conditions including celiac disease, Crohn’s disease, bacterial overgrowth, surgery, or damage from radiation treatments, cites StatPearls.

Large Intestine (Colon)

Most nutrients and water have already been absorbed by the time your food enters your large intestine (colon) — which is about 1.5 meters (5 feet) long — leaving indigestible parts of food like fiber, some water, and dead cells in your digestive tract. The job of your large intestine is to absorb nearly all the remaining water and certain nutrients, the Cleveland Clinic

notes. Your large intestine also secretes mucus to help lubricate its contents as they become dehydrated into stool.

Helpful bacteria in your large intestine break down dietary fiber to produce important nutrients like vitamins B and K, as well as short-chain fatty acids that can be used as energy by the body, the IFFGD notes.

Irritable bowel syndrome — a chronic condition that causes symptoms such as abdominal pain, cramping, bloating, excess gas, diarrhea, or constipation — can occur in either the colon or the small intestine. Another problem that can affect your colon is diverticulitis, in which pouches in your colon known as diverticula — abnormal bulges that typically aren’t a problem by themselves — become infected or inflamed. Extra tissue known as polyps can grow inside your colon, and in some cases can eventually become cancerous — leading to colorectal cancer, the National Library of Medicine


The gut microbiome: Most microbes in the body are located in the gut–made up of both beneficial and potentially harmful bacteria. They are found in the stomach, and the small and large intestines. The gut microbiome plays a critical role in digestion and keeping the immune system healthy. Disruptions in the balance of gut bacteria can lead to diseases such as obesity, inflammatory bowel disease, diabetes, celiac disease, and psoriatic arthritis.


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