Health
How Does the Digestive System Work?
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Stomach
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
notes.
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.
Pancreas
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.
Liver
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
notes.
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.
Rectum and Anus
When stool enters the final portion of your large intestine — your rectum — it triggers the urge to have a bowel movement, the Cleveland Clinic states.
During a bowel movement, your rectum pushes stool through your anus — a short tube that’s about 4 centimeters (1.5 inches) long. Muscles around your anus (anal sphincters) relax, allowing stool to pass from your body, the Mayo Clinic
notes.
Inflammation of the rectum — known as proctitis
— can happen due to an infection, including a sexually transmitted infection (STI). Problems with muscles or nerves in your rectum can make it hard to hold in poop, leading to fecal incontinence (stool leakage). Or you may experience difficulty pooping — known as obstructed defecation — due to problems with your anatomy or your brain and nervous system, including psychological issues such as anxiety or depression, notes the Cleveland Clinic.
If poop stays in your rectum for too long as a result, it can become hard and dry and plug your rectum (fecal impaction).
Problems affecting your anus
can include hemorrhoids — swollen blood vessels that lead to irritation and possibly bleeding — as well as anal fissures (tears in the anus lining) or anal STIs, such as anal warts.
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