Digestive System

The opening in the head through which food enters the body. Even before a person takes an initial bite of food, the sensations provided by sight, smell and even imagination of appetizing food prompts the salivary glands under the tongue to secrete saliva. This prepares the body for the meal to come.

As the teeth grind food into smaller bits, saliva moistens it for easier swallowing. A digestive enzyme in the saliva known as amylase breaks down carbohydrates (sugars and starches). Muscle movements in the tongue and mouth provide the swallowing necessary to push the food into the throat (pharynx). This is a passageway for food and air that is about 5 inches (12.7 centimeters) long. A flexible flap of tissue called the epiglottis reflexively closes over the windpipe during swallowing to prevent choking and to prevent food from entering the lungs.

As the food travels down the throat, it arrives at a junction just above a long, muscular tube known as the esophagus. This junction, called the upper esophageal sphincter, is a muscular valve that opens to allow food into the esophagus. A series of rhythmic contractions in the esophageal wall moves the food down the tube. This process is called peristalsis, and it takes between four and 10 seconds in the esophagus. The muscular movement of peristalsis continues throughout the digestive system. At the end of the esophagus, a muscular ring called the lower esophageal sphincter opens and allows food to enter the stomach. Then it quickly closes to keep the stomach’s digestive juices from flowing back into the esophagus and damaging the tube’s walls.

A large, bean-shaped, hollow muscular organ consisting of three regions: the cardia, the body (fundus) and the antrum. The upper stomach serves as a storage area for food. Here, the cardia and fundus of the stomach relax to make room for food that enters the stomach. Once food enters the stomach, muscles begin to churn and mix the food with acids and enzymes (gastric juices). This breaks down the food into smaller, digestible pieces. Cells in the stomach lining secrete mucus, hydrochloric acid and pepsin, which aid in this process.

Mucus protects the cells of the stomach lining from damage by the acid and enzymes. Any disruption to this layer of mucus, such as from a bacterial infection for example, can result in damage that leads to a stomach ulcer. Hydrochloric acid, also called stomach acid, is produced by parietal cells in the stomach lining and provides the highly acidic environment necessary for pepsin to break down proteins.

At this point, some substances (e.g., water, salt, sugars and alcohol) are ready to be absorbed into the body directly through the stomach wall. However, most substances still require further digestion. Once the food has been processed into a thick liquid called chyme, it is stored in a walnut-sized muscular tube at the bottom of the stomach called the pylorus. Once the chyme achieves the right consistency, a muscle between the stomach and small intestine called the pyloric sphincter opens to allow its passage into the small intestine.

Chyme secreted from the stomach moves down into the small intestine, which is made up of three parts:

• Duodenum. The C-shaped first part.
• Jejunum. The coiled midsection.
• Ileum. The final section leading into the large intestine.

Digestion of chyme continues as it is further broken down in the small intestine until the nutrients can be absorbed into the bloodstream. Millions of microscopic, finger-like projections (villi) cover the wall of the small intestine. Nutrients are absorbed through these villi.

Undigested food and some water moves into the large intestine through another muscular ring that prevents food from returning to the small intestine. The large intestine removes water from the undigested matter and solid waste that can be excreted. The large intestine is made up of three parts:

• Cecum. Pouch that joins the small intestine to the large intestine. The appendix is an even smaller pouch attached to the cecum. The appendix has no known function, but can become inflamed and require surgical removal.
• Colon. A long tube that connects the cecum to the rectum. Bacteria here help digest any remaining food. The ascending colon and transverse colon absorb fluids and salts. The descending colon receives the resulting waste. The sigmoid colon empties the waste into the rectum.
• Rectum. Area below the colon where feces are stored until they are ready to be expelled from the body through the anus as a bowel movement.

A mild condition marked by unpleasant abdominal sensations after eating. Symptoms of indigestion include heartburn, nausea and gas and bloating.

Repeated, loose, watery and often uncontrolled bowel movements occurring more than three times a day.

Inability or difficulty passing feces from the body, resulting in too few bowel movements.

Caused by swallowing air or the breakdown of certain undigested foods by bacteria in the colon, gas in the digestive tract may result in belching, flatulence, bloating and abdominal pain or discomfort.

Inflammation in the stomach lining caused by either a bacterial infection or the chronic use of certain medications such as nonsteroidal anti-inflammatory drugs (NSAIDs), which weaken its protective mucous coating.

Painful, bleeding sores in the lining of the stomach that occur when the protective mucous coating of these organs is weakened. Ulcers may also occur in the esophagus and part of the small intestine.

A condition in which the contents of the stomach flow back (reflux) into the esophagus and damage its lining. GERD occurs when the lower esophageal sphincter, which separates the esophagus and stomach, does not close properly.

Many bacteria, viruses and parasites, sometimes in food or water, may invade the body through the digestive system. They may cause foodborne illnesses and infections such as gastroenteritis.

A common disorder resulting from improper functioning of the muscles in the colon. Symptoms of IBS include abdominal cramping, bloating, constipation and diarrhea.

Chronic inflammation of the intestines. Examples of inflammatory bowel disease include ulcerative colitis, which often affects just the rectum and the colon, and Crohn's disease, which can affect the whole alimentary canal as well as other parts of the body.

A condition characterized by the presence of small, abnormal sacs (diverticula) in the wall of the colon, which may become infected. The sacs occur most frequently in the last section of the large intestine just above the rectum. There may be only a single sac or there may be hundreds.

Inflammation of the esophagus caused by infection or the prolonged use of certain medications, such as NSAIDs.

A condition characterized by inflammation of the gallbladder and usually associated with gallstones.

Inflammation of the liver, which can result in its impairment.

Inflammation of the appendix, a pouch in the large intestine that has no known function. An inflamed appendix can be life-threatening if it bursts, so appendicitis is usually treated with surgical removal, or appendectomy.

Inflammation of the pancreas, most often caused by alcohol abuse or gallstones.

A digestive disorder caused by an abnormal response of the immune system to a protein called gluten that is found in foods containing wheat, oats, rye and barley.

Patients with celiac disease have difficulty digesting nutrients from the foods they eat because gluten damages the lining of the intestines over time. Symptoms of the disorder include diarrhea, bloating and stomach pain.

A congenital condition in which there is a gap between the upper and lower sections of the esophagus, preventing the passage of food and liquids.

A chronic, inherited condition characterized by the overproduction of thick, abnormal mucus, which blocks the ducts or passageways in the pancreas and prevents its digestive juices from entering the intestines. CF patients have difficulty digesting proteins and fats. As a result, important nutrients pass out of the body unused and patients are underweight.

An inability to break down lactose (the main sugar found in dairy products) due to the lack of lactase, a specific digestive enzyme. Patients with lactose intolerance experience symptoms such as gas, bloating and abdominal pain after consuming a food or beverage that contains lactose.

An inflammation of the abdominal cavity and its lining (peritoneum) that typically involves infection. Symptoms of peritonitis include abdominal pain and tenderness, fever and vomiting.

A bulging of part of the intestine that pushes into the groin through a weakness in the abdominal wall. Characterized by pain and feelings of pressure or burning in the groin, inguinal hernia often requires surgical treatment.

A protrusion of the stomach into the chest cavity through an opening in the diaphragm. Hiatal hernia often results in reflux.

A swelling and stretching of the veins in the wall of the anus and rectum. Some people with hemorrhoids experience bleeding, pain and a feeling of fullness in the rectum while others have no symptoms at all.

A condition in which the stomach muscles function improperly, causing food and liquid to pass too slowly into the small intestine. Common symptoms include nausea, vomiting and feeling full early in a meal (early satiety).

A precancerous condition in which the cells lining the lower part of the esophagus are replaced with abnormal cells. The condition is frequently associated with GERD.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions regarding the digestive system:

• Am I at risk for any digestive conditions?
• What changes in the digestive system may indicate an illness?
• For what digestive problems should I consult a physician?
• Why is it important to take care of my digestive system?
• How can I keep my digestive system healthy?
• Can any of the medications I am currently taking affect my digestive system?
• Does my condition require a visit to a gastroenterologist?