Gastroenterology

• ANATOMY OR SYSTEM AFFECTED: Abdomen, gallbladder, gastrointestinal system, intestines, liver, pancreas, stomach, throat

DEFINITION: The subspecialty of internal medicine devoted to the digestive tract and the organs aiding digestion.

Science and Profession

The gastrointestinal (GI), or digestive or alimentary, tract is a hose of layered membranes, about 7 to 9 meters (23 to 29.5 feet) long, that runs from the throat to the anus, allowing matter from the external world to pass through the human body. Along with its allied organs, glands, and nerve networks, the GI passage extracts the nutrients from food that are needed to fuel the body and excretes any substances that are left over. Physicians specializing in the GI system, gastroenterologists, care for everything from the upper esophageal sphincter to the anus; other specialists care for the mouth.

The GI tract has five major sections, each serving a distinct function: the esophagus, stomach, small intestine, colon, and rectum. The esophagus begins where the throat ends, just below the vocal cords. It is a straight tube, usually about 20 to 25 centimeters (8 to 10 inches) long, with a valve at the top (upper esophageal sphincter). When food, formed into a ball and softened by chewing, enters from the mouth, rhythmic waves of muscle contractions (peristalsis) squeeze it smoothly toward the stomach, a trip that lasts about seven seconds. Peristaltic pressure triggers the lower esophageal sphincter to open, dropping the ball of food into the stomach; the sphincter immediately closes so that no stomach acids wash up into the esophagus.

The stomach, an ear-shaped bag that holds 1 to 2 liters of material, has three adjoining sections. First, the fundus, just below the lower esophageal sphincter, stores food. Second, the body mixes hydrochloric acid into the food, which breaks down proteins and kills bacteria, as well as a variety of enzymes, most of which also attack protein; a chemical is also introduced that prepares vitamin B₁₂ for absorption in the small intestine. Third, the antrum grinds the food and pumps it through a sphincter (the pylorus) into the small intestine. Food usually takes from one to six hours to pass through the stomach.

The small intestine, about 3 to 5 meters (10 to 16.5 feet) long, loops and coils in the region from the rib cage to the pelvis. The first major loop, a squared U-shape, is the duodenum. Here, bile from the liver and the gallbladder breaks down fats; water may come in from the blood if the food is salty, and enzymes from the pancreas and intestinal membrane glands continue digestion. The next section, the jejunum, absorbs most of the juices mixed with the food during digestion—up to 8 liters—as well as minerals and nutrients. The last section, the ileum, takes out bile salts and vitamin B₁₂. After about three to five hours, the remnants of food, moved by peristalsis, reach another sphincter, the ileocecal valve.

The ileocecal valve admits the remaining contents into the colon, which is wider and has segments like a caterpillar. Also called the large intestine, it rises along the right side of the body in the ascending colon; turns 90 degrees into the transverse colon, which crosses to the left side of the body; and turns another 90 degrees into the descending colon, which drops to the sigmoid (S-shaped) colon—altogether a passage of more than a meter. The colon receives watery matter from the small intestine each day, and colon bacteria, of which there is a great variety, mix with the solids and complete digestion. The colon absorbs most of this remaining water.

The anorectum is the last stop. The rectum stores fecal matter, the waste products of digestion: bile, bacteria, undigested fiber, cells sloughed from intestinal linings, and mucus. When a sufficient mass has built up, about 100 to 200 grams (3.5 to 7 ounces), pressure signals the time for defecation. The puborectalis muscle, which is under conscious control after toilet training, relaxes, tilting the feces into a vertical position. The anal sphincter opens, and the feces exit the body through the anus as stool. It normally takes from four to seventy-two hours for waste to pass through the colon.

Three organs attached to the GI tract participate in digestion: the liver, the gallbladder, and the pancreas. The liver makes bile, an oily green liquid that aids the absorption of fats and fat-soluble vitamins and which stores and processes absorbed nutrients, as well as removing toxic substances from food. Bile travels from the liver through the common bile duct into the duodenum; along the way, the gallbladder, a small pouch, stores the bile until it is needed. In addition to making insulin, the pancreas secretes various enzymes for digestion into the duodenum via the pancreatic duct.

The enteric nervous system (ENS), or “gut brain,” regulates peristalsis, secretions, and some immune responses throughout the digestive tract, although its mechanisms are not completely understood. The ENS comprises an intricate network of nerves and ganglia laced through the linings of the gut membranes and muscles, and it senses the presence of food through various hormones and neurotransmitters. The vagus nerve connects the esophagus and stomach to the base of the brain; sacral nerves do the same job for the colon. Other nerves reach from the GI tract to the spinal cord.

American humorist Mark Twain advised people to eat whatever they liked and then let the foods fight it out in the stomach. When the GI tract reacts to disagreeable foods, however, the result can be pain; in fact, because of the great number of possible malfunctions (deadly or not), the GI tract is responsible for more discomfort and misery than any other major system.

Gastroenterologists spend the largest percentage of their time treating maladies that cause pain but do no lasting harm. For example, gas, a perennial problem for people of all ages, causes bloating, and its pain is sometimes so severe that it is mistaken for a heart attack. An array of poorly understood functional disorders of the colon, called irritable bowel syndrome (IBS), affects 10 to 15 percent of Americans. Affected individuals have nausea, diarrhea or constipation, and abdominal distress; this condition is popularly known as nervous stomach. Although not dangerous, it produces a bewildering variety of stomachaches. Likewise, chronic stomach and motility irregularities in the esophagus can affect digestion. Proctalgia fugax is intermittent, intense pain in the rectum.

Many GI diseases, however, can be deadly. Various cancers grow in the stomach, esophagus, and, most commonly among Americans, the colon. (Cancers rarely begin in the small intestine.) Gastroesophageal reflux disease (GERD) occurs when stomach juices repeatedly sluice into the esophagus, where they irritate and inflame the membrane. Aside from causing a burning sensation, the juices can erode through the membrane, creating ulcers. If the membrane is eaten through entirely, a hole opens into the body cavity around the gut, spilling food, blood, and digestive juices. Emergency surgery is then needed. Although conventional wisdom has long attributed ulcers to emotional stress or bad habits, such as too much alcohol, research has determined that virtually all people with stomach or duodenum ulcers have a bacterium known as Helicobacter pylori in their gut. H. pylori is a primary cause of ulcers, although high levels of acid or long-term use of aspirin or non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen can produce ulcers independently of the bacteria. H. pylori also plays a role in the development of gastrointestinal cancers, specifically gastric adenocarcinoma and gastric MALT (mucosa-associated lymphoid tissue) lymphoma. Patients with symptoms of ulcers or with cancers of the gastrointestinal tract should be tested for this bacterium and treated with antibiotics. Ulcers can also occur in the stomach and duodenum as a result of motility disorders, excess acid, or drugs that irritate the membrane. Regardless of cause, symptoms of ulcers are exacerbated by motility disorders, excess acid, or drugs, especially alcohol and aspirin, that irritate the membrane.

Colitis and Crohn’s disease are serious inflammations of the gut lining, especially in the colon; except for some forms of colitis that are caused by bacteria, the exact mechanism behind such inflammation remains uncertain. It likely results from a combination of environmental and genetic causes. Colitis and Crohn's disease frequently require surgery to remove damaged and inflamed areas.

Similarly, tears in the gut lining, strictures, passages blocked by chunks of food, exposed veins (varices), infected sacs in the colon (diverticula), and communicable diseases such as dysentery and hepatitis produce potentially deadly symptoms.

Diagnostic and Treatment Techniques

An extensive battery of tests, procedures, and medications enables gastroenterologists to cure or palliate many GI diseases. In addition to the traditional physician’s tools of the physical examination and the patient’s medical history, high-tech instruments let gastroenterologists see inside parts of the gut, produce images of it, remove tissue and stones, stop bleeding, and destroy tumors. Medicines kill bacteria, help regulate motility, speed the healing of damaged tissue, and control diarrhea and constipation. Yet, the GI tract is a very intricate system, and at times, the gastroenterologist’s most effective remedy is sympathy and advice about changing behavior or diet so that patients learn to live with their diseases.

Before treatment can begin, the disease must be identified. An interview with the patient and a medical examination constitute the first step in narrowing the range of possible causes of distressing symptoms. Symptoms described by the patient or discovered by the physician are clues to the underlying causes and suggest the kinds of tests that will most likely isolate the actions of a specific disease. Blood tests can reveal abnormal levels of white cells or chemicals and the presence of infection. Samples of digestive juices likewise can show chemical imbalances, infections, and bleeding, as can stool samples. Biopsies of the gut membrane, liver, and tumors allow pathologists to inspect tissue damage and look for viruses or bacteria. For example, a patient with yellowish skin (jaundice) and a tender liver who complains of nausea and chills may lead a physician to suspect hepatitis. The physician will then order a blood serum test, looking for specific proteins typical of hepatitis infection, and a liver biopsy to learn the type of hepatitis.

Some diseases, especially those destroying or inflaming tissue or involving motility problems, require imaging to identify, as do blockages and strictures. To obtain pictures of the gut, physicians use ultrasonography, X-rays, magnetic resonance imaging (MRI), and computed tomography (CT) scans. Ultrasonographs transmit sound waves through the body and judge the density of tissues by the intensity and pattern of reflection; they are particularly useful for spotting gallstones. X-rays, MRIs, and CT scans pass radiation through the body and record it on film or by sensors that feed data to a computer to construct an image. Plain X-rays show the pattern of air and gas distribution in the digestive tract and can detect obstructions. X-rays may also be taken after barium, a radiopaque element, has been swallowed or inserted in the colon so that it coats the GI tract’s walls and makes them easier to see. Such imaging helps physicians locate strictures, perforations, cancers, diverticula, blockages, and distended areas.

Few tests are more revealing, however, than a direct look inside the GI tract. Until the 1960s, this could not be done without exploratory surgery. At that time, the endoscope became widely available. Developed by British, American, and Japanese scientists, the endoscope is a long, flexible, maneuverable tube filled with fiber optic strands and a central channel for inserting various instruments. A light source at its tip illuminates the area ahead of the scope; the fiber optics collect the reflected light and pass it directly to the eye of the examining physician at the scope’s opposite end, to a television monitor, or to a camera. There are many types of endoscopes, of which three are most common: The meter-long upper gastrointestinal panendoscope (or gastroscope), inserted through the mouth, can be used for seeing well into the duodenum; the 60-centimeter (23.5-inch) flexible sigmoidoscope is used in the rectum and sigmoid colon; and the lower panendoscope (or colonoscope)—180, 140, 100, or 70 centimeters long—inserted through the anus, can be worked through the entire colon and as much as 30 centimeters (12 inches) into the ileum. Most of the small intestine cannot be seen by endoscopy.

With endoscopy, gastroenterologists can spot and examine a diseased or damaged area of the gut and perform a biopsy so that tissue can be examined under a microscope. Yet endoscopes can do even more than that. They can push a wad of food obstructing the esophagus into the stomach, stretch open a stricture, or clear a clogged duct with wires inserted through the scope’s channel; small balloons can be inflated inside the gut to widen constricted passages. Similarly, endoscopes with wire attachments can open a passage between the surface skin and the stomach, allowing food to be put directly in the stomach for patients incapable of swallowing, a procedure called percutaneous endoscopic gastrostomy (PEG). With looped and electrified wires, they can remove polyps, cut away tissue, and cauterize bleeding vessels and ulcers. One such procedure, endoscopic retrograde-cholangiopancreatography (ERCP), can image the biliary and pancreatic ducts and allow removal of gallstones without surgery. Magnetic resonance cholangiopancreatograph (MRCP) is similar to ERCP, but it is a less invasive diagnostic option; however, it does not facilitate performing biopsies, removing stones, or placing stents.

Drugs may also be injected through the endoscope to control bleeding from varicose veins (sclerotherapy), and fiber optics permit the use of lasers to vaporize cancerous tissue. Endoscopic treatments exist for chronic heartburn, including the Stretta procedure, which increases the thickness of the LES using radiofrequency energy. In a minimally invasive procedure, a LINX magnetic sphincter augmentation may treat acid reflux or GERD using a flexible ring of magnetic titanium beads placed around the lower esophageal sphincter that allows food to enter the stomach but limits its return. Similar endoscopy procedures, such as the peroral endoscopic cardial constriction with band ligation technique, can also be used to treat GERD.

Gastroenterologists use drugs to sedate patients during procedures and to treat dysfunctions and diseases. Other medications available are too numerous and their administration too complex to describe in detail, but basically they ease pain, check diarrhea and vomiting, decrease acid production to permit ulcers to heal, soften the stool of constipated patients, control motility problems (such as spasms), regulate secretions, speed coagulation at bleeding sites, or kill harmful bacteria and parasites. GI pain, especially from IBS, is notoriously difficult to treat because of the diversity of contributing causes, including mental health. Researchers produce new drugs each year, but improvements are slow, and new drugs require extensive clinical trials to determine the proper dosage and detect potential harmful side effects. Sometimes, a placebo—a pill with no active ingredient, a “sugar pill”—is enough to make a patient feel better. The interaction between a patient’s gut, nervous system, and personality is intricate and sometimes highly idiosyncratic.

Gastroenterologists do not simply react to disease and trauma with treatments; they also try to prevent trouble from starting in the first place. A large part of their job involves educating patients. They discuss diets that can reduce GI pain and warn against the abuse of drugs, especially alcohol and tobacco, that are known to contribute to heartburn and ulcers. They routinely screen patients over the age of forty-five for cancer, sometimes by endoscopic examination. If there is a family history of cancer, these screenings may begin sooner and be repeated more frequently.

Perspective and Prospects

Jan Baptista van Helmont, a seventeenth-century medical chemist, was the first to describe the diseases and digestive juices of the GI tract scientifically. Gastroenterology can be said to have started with his studies (he also coined the word “gas”). Yet, no one directly observed the operations of digestion until 1833, when US Army surgeon William Beaumont cared for a French Canadian with a bullet wound to the stomach. The wound remained open, and Beaumont could watch the action of gastric juices and the stomach’s mixing and grinding action. Throughout the nineteenth century, there were advances in the understanding and treatment of the GI tract, including the introduction of enemas and gastric lavage (washing out), X-rays, and an early form of endoscopy.

As it did for most branches of medicine, twentieth-century technology greatly expanded the role of gastroenterology in diagnosing, preventing, and treating disease. Imaging and endoscopy, especially, have revolutionized the field. In 1932, Rudolph Schindler developed a flexible gastroscope, and in 1943, Lester Dragstedt performed the first vagotomy (surgically cutting the vagus nerve) to reduce stomach acid secretions. Advances were also made to heal peptic ulcers with a special diet. The second half of the twentieth century witnessed an increasing number of refinements and innovations in procedures, but was most notable for the development of medications, which meant that far fewer surgical procedures were needed for common GI diseases.

Because of these medicines, ulcers rarely require surgery. Gallstones in the common bile duct that once necessitated surgical removal can be taken out during an ERCP; a gastroenterologist can insert a stent (perforated tube) into a blocked bile duct to keep bile flowing from the liver. Screenings for colon cancer and the removal of polyps, which can become cancerous, often identify cancerous or precancerous areas early and permit surgeons to remove tumors before the cancer spreads. Patients who once might have died because of a blocked or strictured esophagus can be treated and quickly released from the hospital. The overall trend led to shorter hospital stays and lower medical costs for common ailments. The sophistication of equipment and the training needed to treat difficult problems, however, inflated costs, as did the tendency to medicate painful ailments that patients once had to steel themselves to endure, such as IBS.

Despite the expansion of gastroenterology’s procedures and knowledge, it is far from an independent field. Gastroenterologists typically act as consultants, caring for patients after they have been screened by family practitioners, emergency room doctors, and internists. Moreover, gastroenterologists rely on pathologists to decipher the information in biopsied tissue samples, radiologists to interpret imaging, neurologists to diagnose nervous system problems, and surgeons to repair perforated gut walls and perform transplants. Finally, specially trained nurses and technicians assist gastroenterologists with various procedures and ensure that patients follow their prescribed dietary and medication regimens.

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