The Intestine is a vital organ in the digestive system responsible for nutrient absorption. Learn about its anatomy, functions, and common health issues.

Intestine: Anatomy and Function

The human intestine is a total of five to seven meters long and lined with mucous membranes on the inside. This is folded in different ways so that there is a strong increase in surface area. This is important for nutrient absorption, the main task of the intestine. Different sections of the intestine have different tasks.

  • Small intestine
  • Large intestine

These two proportions, in turn, can be divided into different sections.

The food pulp from the stomach is transported in so-called peristaltic waves through the tube system of the intestine. In a healthy intestine, this usually only happens in one direction: from the mouth to the anus. At the same time, the wave movement further mixes the food pulp. In the beginning, this is still quite liquid, but the further the food travels through the intestines, the firmer it becomes.

The small intestine

The small intestine can be divided into the following sections:

  • duodenum
  • jejunum
  • ileum


The duodenum (duodenum) begins immediately after the outlet of the stomach and is located in a C-shape in the upper abdomen. It is about 25 to 30 centimeters long – which corresponds to about twelve finger widths.  The ducts of the gallbladder and pancreas open into the duodenum. Here, the chyme from the stomach is mixed with the digestive juices, and the first nutrients are absorbed. In addition, the very acidic contents of the stomach in the duodenum are somewhat neutralized. The duodenum opens into the rest of the small intestine with a slight bend.

Jejunum and Ileum

The jejunum and ileum make up the longest part of the intestine: In total, up to five meters of small intestine loops lie loosely in the abdomen. It is in this section of the intestine that most of the nutrients are absorbed from food. In the Jejunum, these are mainly:

  • water-soluble vitamins
  • Fats (lipids)
  • Salts (electrolytes)
  • and amino acids

The ileum is responsible for receiving:

The ileum usually ends in the right lower abdomen with a valve (also called Bauhin’s valve) into the first section of the large intestine: the appendix. There is a higher density of bacteria in the large intestine than in the small intestine. The valve is designed to prevent intestinal contents (and thus many bacteria) from flowing back from the large intestine into the small intestine.

Large intestine

The large intestine lies like a frame around the loops of the small intestine. It is less motile than the small intestine. In the case of the large intestine, a distinction is also made between different sections that have special tasks. The large intestine consists of:

  • appendix (appendix vermiformis)
  • cecum
  • colon
  • and rectum (with canal)

Behind the valve is a bulge of the intestine in the lower right abdomen: the caecum. It represents the transition to the large intestine. On the caecum there is a small, finger-like appendix (appendix vermiform). This appendix can become inflamed and cause major problems, which – not quite correctly – are known as “appendicitis”.

The appendix is also known as the “intestinal tonsil” because there are many cells in its wall for defense. However, if it is removed because of inflammation, there is no disadvantage.


After the appendix, the colon begins. This has the task of extracting the remaining water from the food pulp so that it becomes formed stool.

The colon is divided according to its course in the abdomen. In the order in which the chyme passes through the sections, these are:

  • ascending colon
  • transverse colon
  • descending colon
  • sigmoid colon
  • rectum

Approximately at the level of the sacrum, the sigmoid colon passes into the rectum, the rectum. Together with the canal, this forms the rectum and ensures the continence of bowel movements and intestinal winds. In this area there are many muscle layers that have to work well together so that bowel movements (defecation) occur, or so that bowel movements can be restrained.

Bowel movements

For many people, this is a shameful topic, but an unavoidable, very natural process. A healthy intestinal flora and regular bowel movements have an impact on our health and well-being. On average, a healthy person excretes about 100 to 200 grams of stool per day.

Diarrhea and constipation

If the normal passage of food pulp is disturbed, problems may arise. If it takes too long for the bowel movement to reach the anus, more and more water is withdrawn from it in the large intestine. This leads to very firm bowel movements: constipation. In the worst case, it can lead to intestinal obstruction. This can also have other, very different causes and therefore leads to different symptoms.

If the food pulp is transported too quickly, it remains very liquid: diarrhea occurs. This contains too much water and is also harder to retain than normal bowel movements.

Bowel screening and colorectal cancer

About one in eight cancers affects the intestine. Colorectal cancer often develops from small bulges of the mucous membranes, called polyps. Colorectal cancer can manifest itself in very different ways:

  • Blood in or on the stool
  • irregular (alternating or new, solid or liquid) bowel movements
  • Pain during bowel movements
  • or no symptoms at all

Since colorectal cancer occurs mainly after the age of 50, various screening examinations are recommended from this age. This is covered by the health insurance company. For example, you can do a stool test for hidden blood or – men from the age of 50 and women and from the age of 55 – also a colonoscopy. In this case, suspicious polyps can also be removed at the same time. Our video shows you how a colonoscopy works in most cases.

Pain in the area

A common cause of pain during bowel movements can be problems that occur directly on the anus or in the anal canal. The skin and mucous membranes here are particularly sensitive, so many people perceive the pain very strongly. The topic is also very taboo, which is why many sufferers do not seek medical advice until late.

Chronic inflammatory bowel disease

According to estimates, more than 80,000 people in Australia suffer from chronic inflammatory bowel diseases. These include Crohn’s disease and ulcerative colitis. They can occur in different phases of life and lead to different, sometimes even life-threatening symptoms. What both diseases have in common is that parts of the intestine become severely inflamed. There are various methods of therapy.


Most people clean the top end of this long tube intensely twice a year when they go for teeth cleaning – but never think of cleaning the other end properly.