Your stomach is as an organ essential for digestion, the process of breaking down food into its smallest particles so your body can absorb nutrients. The process of digestion involves the mixing of food, its movement through the digestive tract, and the chemical breakdown of the large molecules of food into smaller molecules. Digestion of food begins in the mouth, when teeth break the food into smaller particles and amylase, an enzyme in saliva, begins to break down starches into simple sugars. Digestion continues in the stomach.
When it's empty, your stomach resembles an unexpanded J-shaped balloon. It's capable of contracting and expanding to accommodate anything from a snack to a seven-course dinner.
The top part of the stomach secretes gastric acid and a digestive enzyme, pepsin. The lower part of the stomach is more muscular and mixes food with the digestive fluids. With the exception of alcohol and some drugs, absorption of nutrients does not take place in the stomach. When the gastric content is thoroughly mixed and liquefied, it passes into the small intestine, where further digestion of proteins, sugars, and fats occurs and where absorption of nutrients begins. By the time the contents pass through the entire small intestine to enter the colon, digestion is complete and the nutrients have been absorbed. The colon extracts water and some materials such as vitamins K and B-12 and begins to form stool.
Common problems of the stomach include:
Gastroesophogeal reflux disease (GERD). The most common symptom of this condition is heartburn. Its cause is a failure of lower esophageal sphincter, the circular muscle between the esophagus and stomach, to close properly. This allows the return of food and stomach juices into the esophagus. When refluxed stomach acid touches the lining of the esophagus, it causes a burning sensation in the chest or throat called heartburn. Occasional heartburn is common but does not necessarily mean that you have GERD. If it occurs more than twice a week, it may be GERD and can lead to more serious health problems. It can be caused by a hiatal hernia (when the upper part of the stomach is above the diaphragm); excessive alcohol use; being overweight; pregnancy; and smoking.
Gastritis. Gastritis, or inflammation of the stomach lining, is a symptom, not a disease. It can be caused by drinking too much alcohol, prolonged use of some medicines such as aspirin or ibuprofen, by the bacterium Helicobacter pylori (H. pylori), or some diseases. The most common symptoms are abdominal upset or pain, belching, bloating, nausea, vomiting, and a feeling of burning in the upper abdomen. Sometimes it causes the stomach to bleed, which requires immediate medical attention.
Peptic ulcer. A peptic ulcer is a sore on the lining of the stomach or duodenum, the beginning of the small intestine. Peptic ulcers can be caused by bacterial infection with H. pylori; by long-term use of nonsteroidal anti-inflammatory agents like aspirin and ibuprofen; and, in rare cases, by cancer of the stomach or pancreas. Peptic ulcers are not caused by stress or eating spicy food, but these can make ulcers worse. The most common symptom of a peptic ulcer is a dull, gnawing ache in the stomach that comes and goes for a period of time. The ache occurs two to three hours after eating or in the middle of the night, when the stomach is empty. The pain is made better by eating or taking antacid medications. Some people have no symptoms. A sudden, sharp stomach pain or bloody or black stools or blood in vomit means that immediate medical care is needed.