What is gastroenterology? |

Science and Profession

The gastrointestinal (GI), or digestive or alimentary, tract is a hose of layered membranes, about seven to nine meters 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 performing a different service: the esophagus, the stomach, the small intestine, the colon, and the anorectum. The esophagus begins where the throat ends, just below the vocal cords. It is a straight tube, about twenty to twenty-two centimeters 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 one to two 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 three meters 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 eight 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 ninety degrees into the transverse colon, which crosses to the left side of the body; and turns another ninety 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, 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 wastes 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 15 to 20 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, 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, recent research has determined that virtually all people with stomach or duodenum ulcers have a bacterium known as
Helicobacter pylori
in their gut. Most scientists now believe that H. pylori may be necessary for ulcers to form, although there is still some question about whether high levels of acid or long-term use of aspirin can produce ulcers independently of the bacteria. H. pylori may also play a role in the development of gastroenterological cancers. Patients with symptoms of ulcers or with cancers of the gastrointestinal tract should be tested for this bacteria and treated with antibiotics. Ulcers can also occur in the stomach and duodenum as a result of motility disorders, excess acid, or drugs, especially alcohol and aspirin, 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 mechanism behind such inflammation remains unknown, but the disorders 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 enable 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 radioopaque 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 the physician to 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 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 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. 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 EndoCinch, a procedure that strengthens the lower esophageal sphincter (LES) by putting in stitches that pleat the tissue, and the Stretta procedure, which increases the thickness of the LES using radiofrequency energy. Endoscopy 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 irritable bowel syndrome, is notoriously difficult to treat because of the diversity of contributing causes, including emotional problems. Researchers turn out a steady supply of new drugs each year, but improvements are slow, and new drugs require extensive clinical trials to determine proper dosage and detect harmful side effects. Sometimes, a placebo—that is, 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 fifty for cancer, sometimes by endoscopic examination, especially if there is a family history of cancer.

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 saw an escalating number of refinements and innovations in procedures but was most remarkable for the development of drugs.

This progress has meant that far fewer surgical procedures are needed for common GI diseases. Because of new medicines, ulcer disease rarely requires surgery. Gallstones in the common bile duct that once necessitated surgical removal now may be taken out during an ERCP; a stent (perforated tube) can be inserted into a blocked bile duct under a gastroenterologist’s guidance 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, sometimes making surgery unnecessary. Patients who once might have died because of a blocked or strictured esophagus can now be relieved and quickly released from the hospital. The overall trend has been shorter hospital stays and lower medical costs for common ailments. The sophistication of equipment and the training needed to treat difficult problems, however, have correspondingly inflated costs, as has the tendency to medicate painful ailments that sufferers once had to steel themselves to endure, such as irritable bowel syndrome.

Despite the expansion of gastroenterology’s procedures and knowledge, it is far from an independent field. Gastroenterologists typically act as consultants, caring for patients only 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 trace nervous system problems, and surgeons to repair perforated gut walls and remove diseased organs or transplant new ones. Finally, specially trained nurses and technicians must help them with many procedures and ensure that patients follow prescribed dietary and drug regimens.

Bibliography

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