The stomach is a muscular sac that is located principally in the left upper abdomen. In the average adult, it is the size of a small melon. However, it can dramatically stretch when filled with food and liquid and hold nearly one gallon. When the stomach is empty, it tends to fold in on itself. Enzymes that are secreted in the mouth begin the process of digestion. From there, food passes through the esophagus, a muscular tube that connects the throat to the stomach and is about 10 inches long. At he junction of the esophagus and stomach there is a muscular valve, the lower esophageal sphincter. As it relaxes, foods and liquids are allowed to pass into the stomach. The walls of your stomach are lined with three layers of powerful muscles that churn food into smaller pieces and mix it with enzymes and acids produced by glands in the stomach's inner lining. Under normal conditions, your stomach produces 2 to 3 quarts of gastric juices every day. Acid is secreted by the stomach in the form of hydrochloric acid. It is very corrosive. However, the stomach's delicate tissues are protected from this powerful acid by a thick, jelly-like mucus that coats the stomach lining. Once the food in your stomach is thoroughly broken down and mixed, muscular contractions push it toward the pyloric valve, which leads into the upper portion of your small intestine or duodenum. The valve opens just enough to release barely an eighth of an ounce of food at a time. It may take three to four hours for your stomach to empty after you eat, depending on your diet. Foods high in fat increase the amount of time it takes for your stomach to empty. Over the past 50 years, the incidence of stomach (gastric) cancer has declined dramatically in the United States and western Europe. But the disease remains a grave problem in much of the rest of the world — especially in Asia, eastern Europe and parts of Latin America, where it's second only to lung cancer as a cause of cancer deaths. Scientists have identified several factors that play a role in the development of stomach cancer. Among these is infection with a type of bacterium called Helicobacter pylori (H. pylori), a leading cause of stomach irritation and ulcers. Countries such as China and Colombia, where at least half the children are infected with H. pylori, have a correspondingly high prevalence of stomach cancer. Heavily salted, smoked and pickled foods also are known to cause stomach cancer, and the disease is more common in countries where these foods form a large part of the diet. When refrigeration replaces salting and pickling as a way of preserving food, the incidence of stomach cancer declines significantly. Stomach cancer is more readily treated when caught early. Unfortunately, by the time it's diagnosed the disease is often at an advanced stage and may have spread beyond the stomach to nearby lymph nodes or to other organs such as the liver, pancreas and colon.
Causes of Gastric Cancer
Adenocarcinoma, a form of cancer that comes from the glandular cells in the stomach lining, comprise the majority of stomach cancers. Other tumors, such as lymphomas and sarcomas may also arise from the stomach’s lymphatic tissue or muscle, respectively. A small portion of these tumors are carcinoid tumors. The develop from the stomach’s hormone producing cells. Many stomach cancers spread of metastasize throughout the stomach or expand into the esophagus or small intestine. By spreading through the lymph nodes and lymphatic system, they may also spread to other organs such as the liver, pancreas or colon. Carcinoid tumors spread less commonly. Cell division and cell growth is controlled by the cell’s genetic material, DNA. When the DNA is damaged, control of cell division no longer occurs. Eventually, a mass of malignant cells, or tumor, will develop. Factors that have been found to increase the risk of developing cancer of the stomach include: H. pylori infection, Nitrates and nitrites, salted, smoked or pickled foods, smoking and alcohol consumption and low socioeconomic levels. Nearly two-thirds of the world's population is infected with corkscrew-shaped bacteria called Helicobacter pylori (H. pylori) that live deep in the mucous layer that coats the lining of the stomach. Although it's not entirely clear how the bacteria are transmitted, it's likely they spread from person to person through the oral-fecal route or are ingested in contaminated drinking water. H. pylori infection frequently occurs in childhood and can last throughout life if not treated. It's now known to be the primary cause of stomach ulcers, accounting for at least 80 percent of all cases. It may also be the main cause of stomach cancer. According to the World Health Organization, close to half the annual new cases of stomach cancer can be attributed to H. pylori infection. Due to poor hygiene and crowded living conditions, this organism is more prevalent in low socioeconomic states. Having ulcers doesn't necessarily put you at higher risk of stomach cancer, but having H. pylori infection does. That's because long-term infection causes inflammation that can lead to precancerous changes in the stomach lining. One of these changes is atrophic gastritis, a condition in which the acid-producing glands are slowly destroyed. It's likely that low acid levels prevent cancer-causing toxins from being properly broken down or flushed out of your stomach. Nitrates are naturally occurring chemical compounds that form when bacteria in the soil break down nitrogen. Great quantities of these compounds drain into the water supply from fertilizers, livestock and poultry farming. Nitrates are also added to many processed meats to preserve color and enhance flavor. Excessive exposure of the stomach to these compounds can lead to damage of the stomach lining and possible gastric cancer formation. In your stomach, certain bacteria, including H. pylori, convert nitrates into nitrites, another nitrogen-based chemical. Nitrites are also added to certain foods, especially cured meats such as ham and bacon. The nitrites may eventually form N-nitroso compounds — powerful carcinogens that are known to cause stomach cancer. Preserved foods often contain large amounts of nitrites and nitrates, which can be converted in your stomach into cancer-causing compounds. Countries where consumption of salted meat and fish and pickled vegetables is high — Japan is a notable example — tend to have correspondingly high rates of stomach cancer. Eating a diet high in red meat, especially when the meat is barbecued or well done, has also been linked to stomach cancer. Tobacco and alcohol use have both been linked to the development of stomach cancer. These individuals are more prone to develop cancer in the upper part of the stomach closest to the esophagus.
Signs and Symptoms of Gastric Cancer
The most common sign associated with the development of tumors of the stomach is internal bleeding. Early on, this bleeding may be microscopic and only detected by tests of your stool for blood. Later, the bleeding may be more serious. Due to anemia, or low blood counts, fatigue and loss of strength may occur. If abdominal pain occurs in the early stages of stomach cancer, it my be alleviated by foods or antacids. When the cancer is more advanced, you may experience pain in the upper or middle region of your abdomen. This pain may not be relieved by food or antacids. In addition, abdominal discomfort may be aggravated by eating. Other signs of stomach cancer may include black, tarry stools. Vomiting of blood may occur. Vomiting after eating may occur. Weight loss, fatigue and weakness may develop. Last, there may be a rapid feeling of fullness, even when eating less than normal. Having one or more of these signs and symptoms doesn't necessarily mean you have stomach cancer. Other conditions, especially peptic ulcers, can cause similar problems.
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Medical Content Last Updated on 07/12/2008
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