The intestine - structure, function and common diseases

The tubular intestine consists of the small intestine and the large intestine. When fully functional, the entire intestine stretches for around four meters. If the intestine relaxes after a person's death, it can measure up to six meters. The digestion of food takes place along this long path. The intestine breaks down the food pulp into its components, absorbs vital nutrients into the body and sends them on into the bloodstream.

The structure of the intestine

The small intestine connects to the outlet of the stomach and is divided into the following parts:

• Duodenum
• Empty intestine (jejunum)
• Crooked intestine (ileum)

The large intestine is located in the abdomen with the following sections

• Appendix (cecum) with the vermiform appendix (vermiform appendix)
• Large intestine (colon)
• rectum (rectum)

Nutrients find their way into the body in the small intestine

The small intestine begins as a curved C-shaped tube directly behind the stomach outlet. It absorbs digestive secretions from the gallbladder and pancreas along its approximately 30-centimeter-long path. Ulcers can develop at its upper end. The effect of acidic gastric secretions favors this process.

Empty intestine and small intestine complement the duodenum

The small intestine is very mobile and is attached to a ligament, the so-called mesentery, on the back wall of the abdominal cavity. The mesentery consists of fat and connective tissue. It holds the coiled small intestine and the large intestine in the lower abdomen and supplies both with nerves, blood vessels and lymph vessels. After digestive secretions have mixed with the chyme from the stomach in the duodenum, the actual absorption of nutrients into the body begins. The small intestine breaks down the pre-digested food into molecules. This produces amino acids and free fatty acids, for example. The human organism now absorbs these tiny food components through the intestinal mucosa into the blood. Doctors call this absorption. Indigestible substances and water remain in the small intestine.

Diseases that occur in the small intestine

• Crohn's disease
• Intestinal obstruction (ileus), mechanical or due to muscle paralysis
• Mesenteric infarction
• Meckel's diverticulum
• Upper mesenteric artery syndrome

The large intestine

Once the chyme has passed through the small intestine, there are hardly any nutrients left. This is followed by the large intestine with a length of around 150 centimeters. The complicated mucosal surface of the small intestine gives way to a relief with so-called crypts, small indentations that considerably increase the surface area of the intestine. Mucous glands are an important feature of this section of the intestine. Their mucus makes the feces, which are now formed from the former chyme, slippery. Even without the intake of food, feces are formed from mucus and exfoliated cells of the intestinal mucosa. In the large intestine, water and salt migrate into the body. This is an important regulatory measure for the fluid balance. This section of the intestine is also home to the healthy germs of the intestinal flora. They fight off invading germs.

The cecum is the shortest part of the large intestine

The cecum valve separates the small intestine from the large intestine and protects both sections from the exchange of secretions and bacteria of the intestinal flora. The vermiform appendix (appendix vermiformis), which is commonly referred to as the cecum, adjoins the cecum itself. This smallest section of the intestine is left over from evolutionary history and works together with the immune system. It is notorious for its inflammation (appendicitis), which can sometimes be life-threatening, more on this in the video:

The colon frames the abdominal organs

This is followed by the main part of the large intestine, which doctors call the colon. It lies like a frame in the abdominal cavity and measures up to one meter. Inside it, it thickens the stool to around 200 milliliters per day. If the function of the large intestine is restricted due to infections or inflammation, diarrhea, constipation and flatulence can occur. The body loses too much water and salt and is at risk of dehydration or the stool thickens too much.

The long journey ends with the rectum

The stool covers the last 20 centimetres of its journey in the rectum. It is also collected here until a sufficient amount triggers the reflex that leads to regular defecation. Three different muscle layers seal the anal canal, through which the stool finally leaves the bowel.

Diseases of the large intestine

• Appendicitis ("appendicitis" in the vernacular)
• ulcerative colitis
• diverticulosis
• diverticulitis
• Infectious diarrheal diseases
• polyp formation
• colon cancer
• hemorrhoids
• irritable bowel syndrome

The intestine at the doctor

The gastroenterologist is the specialist for the bowel and stomach. They use ultrasound and colonoscopy, for example, to investigate symptoms such as diarrhea, chronic constipation, abdominal pain and blood in the stool.

During a colonoscopy, the examiner looks directly into the patient's bowel with a small illuminated camera attached to a long flexible rubber tube. He takes mucosal samples and performs small surgical procedures directly on site. The doctor pushes the necessary instruments through a working channel on the examination device. You usually have the option of using a sedative to make the examination more comfortable.

The following videos show what intestinal diseases look like during a colonoscopy:

Conclusion

The human intestine is a fascinating organ with many different sections and tasks. Over a length of around four meters in a living person,it digests food and excretes excess waste. As an important part of the immune system, it fends off germs and deals with allergic reactions. If you know the details of the most important digestive organ, you will also gain a better understanding of its diseases.