Function of the duodenum
The small intestine is divided into three sections. The first section, which directly adjoins the stomach, is the duodenum. It got its name because of its length of about 12 finger widths.
After the stomach has mainly mechanically crushed the food and with the help of the gastric acid has almost completely freed the food pulp from bacteria and other microorganisms, it reaches the duodenum. There the food pulp is first neutralized, as it would otherwise injure the mucous membranes of the intestine due to its low pH value. For this purpose, a duct, the Ductus pancreaticus, opens into the duodenum, through which an alkaline secretion is released from the pancreas.
Together with this duct, the bile duct (Ductus choledochus), which carries the bile, also flows into the duodenum. The bile is produced in the liver and then stored in the gallbladder until it is needed in the duodenum for the digestion of fats and fat-soluble vitamins. In addition, cells located in the mucous membrane of the duodenum produce enzymes that initiate the digestion of the individual nutrients.
Finally, water is added to the chyme here. The actual digestion of the food, i.e. the breakdown of the nutrients contained in the food, takes place in the duodenum. Only later, in the rear two sections of the small intestine, are the nutrients actually absorbed into the body.
Enzymes are special proteins that catalyze reactions. This means that they accelerate the process and reduce the energy needed for the reaction. Enzymes are added to food in the duodenum.
There they split the nutrients contained in the food into their smallest units so that they can be absorbed by the intestine. Each individual class of nutrients has its own highly specific enzymes. Proteins are split by so-called proteinases, for example trypsin, fats by lipases and the various types of sugar by amylase, lactase, isomaltase and maltase-glucamylase.
The products are amino acids in the case of proteins and simple sugars such as glucose and fructose in the case of polysaccharides. The breakdown of fats produces individual fatty acids. This degradation of our food represents the actual process of digestion and is necessary because transporters across the cell membranes are only available for the small nutrient components.
The amylases and lipases come from the secretion of the pancreas. The other enzymes come with the food pulp from the mouth and stomach into the duodenum and some of them are produced directly by cells of the duodenum. The most common disease of the duodenum is the duodenal ulcer (Ulcus duodeni).
The lesion is usually located shortly after the exit from the stomach (pylorus) and can have various causes. These include stress, a bacterial infection (Helicobacter pylori), hyperacidity of the intestine, for example due to gastric acid, or the permanent intake of anti-inflammatory drugs such as aspirin. A duodenal ulcer initially manifests itself as severe pain in the middle upper abdomen and severe nausea.
In addition, irregular bowel movements and unwanted weight loss can be the consequences of a duodenal ulcer.In particularly severe cases, severe bleeding of the upper digestive tract or even a rupture of the duodenum may occur. In such a situation the ulcer should be treated surgically. In some cases, however, the ulcer is completely asymptomatic and is discovered more by chance during routine examinations.
In addition to antibiotics, so-called proton pump inhibitors such as omeprazole and pantoprazole are available for drug treatment. These inhibit the gastric acid produnction and should thus protect against further overacidification of the duodenum. 90% of patients are free of duodenal ulcers after such therapy.
In the area of the duodenum, inflammations, i.e. strong immunological reactions, can occur due to various causes. Firstly, an inflammation of the stomach (gastritis) can spread to the duodenum. On the other hand, the cause can also be the ingestion of drugs that irritate the mucous membrane and thus make it sensitive to the smallest injuries and an infestation with disease-causing substances.
Similar to cancer, inflammatory cells can also migrate from the pancreas into the duodenum or even infiltrate and damage the intestinal wall from the outside. Inflammation does not always have to manifest itself through symptoms, but abdominal pain, fatigue, nausea and anemia can occur. Anemia occurs because blood flow increases in the area of an inflammation, while at the same time the vessels can become more fragile.
Small amounts of blood then escape and are excreted with the stool. In order to be able to confirm the diagnosis, tissue samples must be taken endoscopically from the duodenum and examined by a pathologist. The treatment is based on the cause.
So if there is a bacterial inflammation, antibiotics can be given. In addition, drugs that promote inflammation should be avoided. These drugs include non-steroidal anti-inflammatory drugs such as aspirin (ASS).
However, duodenal inflammation can also take on a chronic, i.e. persistent form. This is called a chronic inflammatory bowel disease. One such chronic inflammation is Crohn’s disease, the cause of which is still unknown today.
It occurs only very rarely in the duodenum and is usually found in the ileum. The symptoms correspond to those of a normal inflammation. However, due to the still unknown cause, the therapy aims especially at eliminating complications, such as additional bacterial infections in the area.
The disease progresses in relapses, so in acute situations strong anti-inflammatory drugs such as glucocorticoids can be given. Duodenal cancer is fortunately extremely rare. Cancer of the colon and rectum is much more common.
There are various causes for this, although not all of them have been clarified yet. Firstly, the temporal aspect plays a role, because the food pulp is only briefly in the small intestine and especially in the duodenum, while it remains in the large intestine for up to days. This means that the contact time of pollutants and potentially carcinogenic substances contained in the food with the mucous membrane of the colon is much longer.
And the longer this time, the more likely it is that the substances are actually absorbed into the body. Another possible explanation lies in the function of the duodenum. As already mentioned, enzymes and fluids are mainly released from the cells of the mucous membrane.
Thus, no cellular mechanisms are available that could absorb substances into the cells in the first place. The situation is completely different in the subsequent sections of the small intestine. There, special transporters are found in the cell membranes, which enable the absorption of food components and thus also possible pollutants.
Once cancer cells appear in the duodenum, they usually originate from a tumor located in the pancreas. Since these two organs are very close to each other, it is very easy for cancer cells to spread from the pancreas into the duodenum. In contrast to duodenal cancer, ulcers in this area of the small intestine occur much more frequently and are also called duodenal ulcers.
Ulcers are defects of the mucous membrane that can extend into the deepest layers. As a result of an infection or circulatory disorder, an area is no longer sufficiently supplied with blood and immune cells, which causes it to slowly lose its function and eventually die. There are people who have an increased risk of developing ulcers due to their genes.Usually the cause is due to the intake of drugs, such as aspirin, which prevent the formation of gastric mucus.
As a result, the stomach and subsequent duodenum are no longer sufficiently protected against the very acidic gastric juice and are attacked by the acid. These superficial injuries then spread to deeper and deeper layers of the multi-layered intestinal wall and thus cause the ulcers. In many cases, the bacterium Helicobacter pylori can also be the cause of gastritis, i.e. inflammation of the stomach.
This can then develop into an ulcer. The most common symptom is probably abdominal pain, followed by the symptoms of anemia, such as fatigue and paleness. The anemia is caused by a small, albeit constant, loss of blood through the ulcer.
