You know what food looks like when it enters your mouth, and what comes out the other end. For many people, though, what happens in between — the journey through the digestive system — is a potentially confusing process. But it doesn’t have to be. Here’s a step-by-step guide to how your digestive system works, along with health conditions that can develop in each part of your digestive tract.

Mouth

Even before you bite into your food, your digestive system kicks in. There’s a reason why we say “mouthwatering” food. Seeing and smelling food causes an increase in saliva (spit) production, ensuring that your mouth will be ready to chew and swallow what it’s about to receive, the Cleveland Clinic

reports.

Saliva lubricates your mouth and throat, making it easier to chew and swallow your food and protecting your teeth from harmful bacteria. It also contains an enzyme that begins to break down starches, according to the National Institute of Diabetes and Digestive and Kidney Diseases

(NIDDK).

Your saliva also helps protect and maintain your teeth, along with protecting and even repairing the soft tissue in your mouth. That means that if you don’t produce enough saliva — known as salivary gland dysfunction — not only will you have trouble chewing and swallowing, but your dental and oral heath can also be affected, notes an article

published in Oral Diseases.

Your tongue contains taste buds and is used to manipulate food as you chew, as well as to push your food through the back of your throat when you swallow, says the National Cancer Institute.

Esophagus

Your esophagus is a tube that extends from the back of your throat down to your stomach, near the middle of your abdomen. It contains muscle tissue that creates a wavelike motion to draw food through it — something that happens in much of your digestive tract, according to the International Foundation for Gastrointestinal Disorders

(IFFGD).

Difficulty swallowing — known as dysphagia — can occur either as you swallow or while food travels through your esophagus. This can happen due to problems such as a physical obstruction (narrowing or blockage, potentially due to a tumor) or motor (muscle function) problems. Motor problems in your esophagus can be caused by conditions such as diffuse esophageal spasm (when your esophagus squeezes in an uncoordinated way), scleroderma,

or diabetes, notes the National Library of Medicine.

At the bottom of your esophagus, at the opening to your stomach, is a ring-shaped area of muscle fibers called the lower esophageal sphincter. This area opens up when food reaches it (or if you need to burp), but normally stays closed to prevent your stomach contents from entering your esophagus, the NIDDK states. And if you need to vomit, this muscle will relax while stomach contractions push your food back up.

If your lower esophageal sphincter relaxes when it shouldn’t, stomach acid can travel up into your esophagus — known as gastroesophageal reflux disease or acid reflux. Over time, stomach acid can damage your esophagus, potentially leading to a change in its lining known as Barrett’s esophagus,

according to University of Michigan Health.

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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