Stomach and Duodenum
What is the Duodenum?
The stomach is a J-shaped sac connecting the esophagus above and the small intestine below. The first part of the small intestine is known as the duodenum. The stomach varies considerably in size, shape and position but lies in the upper central part of the abdomen behind the lower ribs. Although it is a single organ, several different parts of the stomach exist: the fundus, body, antrum and pylorus. The pylorus is the small channel leaving the stomach and food passes through here to enter the duodenum where further digestion occurs.
The stomach wall is composed of four layers. The inner lining (mucosa) consists of millions of microscopic glands which secrete gastric juices. Beneath this is a supporting layer (submucosa) and beneath this is the muscle layer. This is responsible for stomach contractions and emptying. Finally there is a thin outer covering known as the serosa. The duodenum has much the same structure but does not secrete acid.
The stomach and duodenum have a rich blood supply, derived from the aorta (the main artery in the body) and are also supplied by nerves from the spinal cord. These help to control the functions of the stomach.
Function and Control
The stomach carries out several different functions. It acts as the major store for food during a meal and can hold up to 1.5 litres of food and fluid. Special cells (parietal cells) in the glands of the inner lining of the stomach secrete powerful hydrochloric acid that help break down food in the stomach. Other special cells release protein-digesting enzymes (pepsinogens) which become active in the acid environment and begin digesting protein. The stomach secretes a number of other important substances including hormones to regulate the functions of the stomach, mucus to protect the gastric lining from damage by acid, and a substance (intrinsic factor) which is necessary for the body to absorb vitamin B12 from the diet.
Coordinated contractions of the stomach are important for grinding and mixing ingested food with the gastric secretions. This ensures good mixing of stomach contents and also helps to filter out partially digested food to prevent large pieces from entering the duodenum. Lastly, partially digested food and liquids are carefully emptied from the stomach, through the pylorus, into the duodenum. These processes of secreting gastric juices, mixing food and gastric emptying are normally carefully regulated and involve the coordinated action of hormones, nerves, and muscles.
Once food enters the duodenum, its acidity is neutralized by mixing with alkaline juices from the pancreas and bile in preparation for further digestion and absorption lower down the small intestine.
Disorders of the stomach and the duodenum are extremely common and a considerable source of suffering in the population. Upper abdominal pain, indigestion and heartburn may affect up to 25% of the population each year and these symptoms cause suffering, fear about serious disease, time off work and reduced quality of life. Physician visits, costs of investigation and treatment and the days lost from work are also very costly to the economy.
Problems may arise from a number of different mechanisms and lead to a variety of symptoms. The integrity of the inner lining (mucosa) of the stomach depends on a careful balance between the "aggressive" factors (such as acid) which tend to damage the lining and "defensive" factors (such as mucus) which help to protect the delicate surface lining. Disruption of this balance caused by too much acid (or weakened defense) can result in erosions or ulcers with symptoms including upper abdominal pain, indigestion or heartburn, nausea and/or vomiting.
In other patients, symptoms may result from problems with stomach emptying. This can either be the result of a physical blockage (i.e. scarring from an ulcer or a malignant tumor at the pylorus) or else it can result from abnormal control of stomach emptying (known as gastroparesis). Symptoms include abdominal pain, bloating, nausea, vomiting after meals, lack of appetite and early satiety (inability to eat a full meal or feeling full after only a small amount of food).
Erosions, ulcers and tumors may cause bleeding. If the bleeding is brisk and of sufficient quantity it may result in vomiting of bright red blood (hematemesis). Blood which has been in the stomach for any length of time undergoes partial digestion and turns black in color. This leads to vomiting of black fluid ("coffee grounds") or the passage of sticky black stools (melena) as the blood passes down through the digestive tract. A small percentage of ulcers and other abnormalities in the stomach bleed very slowly over a long time and the patient is unaware of the bleeding. Eventually the body's iron stores run out and anemia develops. Gastrointestinal bleeding is discussed further below.
Ulcers, tumors and other stomach problems may all produce very similar symptoms and it is not possible to determine the cause from symptoms alone. Patients with persistent or worrying symptoms require investigation, usually by endoscopy, to make a diagnosis and select appropriate treatment.
Diet is believed to be important in the development of upper abdominal symptoms but there is little scientific evidence to incriminate individual foods or dietary components in causing particular symptoms. There is no specific diet which is known either to predispose to (or protect against) the development of peptic ulcers. In general, a sensible, balanced and healthy diet is recommended but people should avoid foods which they feel clearly upset their stomachs or provoke symptoms. Regular, unhurried meals are also important.
Smoking is an important factor in causing disorders of the stomach and duodenum. Tobacco contains compounds which increases acid production, impair production of protective mucus and damage the lining of the stomach, thereby predisposing to erosion and ulcers.
A variety of medications may cause problems in the stomach and duodenum. Aspirin and other anti-inflammatory drugs (non-steroidal anti-inflammatory drugs, NSAID's) used to treat muscular and arthritic pain, commonly damage the stomach lining and cause erosions, ulcers and bleeding from the stomach and duodenum. Other medications interfere with gastric emptying and cause nausea, bloating or vomiting. If you suffer from problems with your stomach, you should always consult your doctor before taking any new medications.
The role of psychological stress in the development of symptoms of indigestion and peptic ulcer disease is not clear. Periods of stress can make most medical conditions worse but whether stress specifically predisposes people to the development of peptic ulcers is not clear at present.