Your stomach is as an organ needed for digestion. Digestion is the process of breaking down food into its smallest particles so your body can take in 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 starts in the mouth. Teeth break the food into smaller particles. Next, an enzyme in saliva starts to break down starches into simple sugars. Digestion continues in the stomach.
When it's empty, your stomach looks like an unexpanded J-shaped balloon. It's capable of making itself smaller and larger to accommodate anything from a snack to a large dinner.
The top part of the stomach makes gastric acid and pepsin, a digestive enzyme. The lower part of the stomach is more muscular and mixes food with the digestive fluids. With the exception of alcohol and some drugs, the absorption of nutrients does not take place in the stomach. When the gastric content is completely mixed and liquefied, it passes into the small intestine. This is where more digestion of proteins, sugars, and fats happens and where the 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 fully absorbed. The colon draws out water and some materials like vitamin K begin to form stool.
Common problems of the stomach include:
GERD (gastroesophageal reflux disease). This is a problem of the esophagus. The most common sign of this condition is heartburn. The circular muscle between the esophagus and stomach is the lower esophageal sphincter (LES). This muscle always relaxes to let food in and air back up. Sometimes the muscle opens too often. This lets 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 it does not necessarily mean that you have GERD. If it happens 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. This is when the upper part of the stomach is above the diaphragm. Other causes are eating fatty foods, drinking caffeinated or carbonated beverages, drinking too much alcohol, being overweight, being pregnant, and smoking. GERD may also be caused by nonacid reflux.
Gastritis. Gastritis is inflammation of the stomach lining. This disease can be caused by too much alcohol use, long-time use of some medicines such as aspirin or ibuprofen, bacteria called Helicobacter pylori (H. pylori), and some diseases. The most common symptoms are stomach upset or pain, belching, bloating, nausea, vomiting, and a feeling of burning in the upper abdomen. Sometimes it causes the stomach to bleed. If this happens, you need medical care right away.
Peptic ulcer. A peptic ulcer is a sore on the lining of the stomach or duodenum. The duodenum is the start of the small intestine. Peptic ulcers can be caused by an infection with bacteria called H. pylori or long-term use of nonsteroidal anti-inflammatory drugs such as aspirin and ibuprofen. In rare cases, peptic ulcers are caused 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 happens 2 to 3 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 medicines. Some people have no symptoms. A sudden, sharp stomach pain, bloody or black stools, or blood in vomit means that you need medical care right away.