Small intestine
The small intestine' (lat. intestinum tenue) is the longest tubular organ of the digestive system. It comprises the part of the intestine from the exit of the stomach to the Bauhin valve, which marks the transition to the large intestine (lat. Intestinum crassum). The small intestine is of great importance for digestion and nutrient absorption.
Anatomy
Division
The small intestine can be roughly divided from oral to aboral into three intestinal segments of different lengths:
- duodenum (lat. duodenum')
- empty intestine (lat. jejunum)
- ileum (lat. ileum)
In total, it reaches a length of approximately 5-6 meters in an adult. The shortest section is the duodenum, which is about 24 centimeters or 12 finger widths long. This is followed by the middle section of the intestine, the jejunum. This also marks the beginning of the lower gastrointestinal tract. The last section before the adjacent intestinum crassum is the ileum. There is no clearly demarcated transition between the jejunum and ileum.
Projection onto the trunk
The intestinal loops of the small intestine normally lie intraperitoneally and are framed by the colon above and on both sides. Downward, the loops extend into the pelvic inlet (lat. apertura pelvis superior).
The duodenum forms a C-loop which is open to the left and can be localized to the right of the spine in the upper abdomen. A projection to the vertebral bodies includes the region of the L I-III or L IV vertebrae. Frequently, the duodenum lies posterior to the transverse colon of the large intestine and accommodates the caput pancreatis in its curve.
A large part of the small intestine is attached to the posterior abdominal wall by means of the small intestinal crest (mesentery) and is thus in elastic suspension. Due to the high mobility of the intestinal loops, an exact geographical indication based on the skeletal structure is not possible.
Relationship to neighbouring organs
The distal opening into the duodenum is formed by the ostium pyloricum with the pylorus (gastric sphincter/gastric gate). This regulates the amount of food pulp in the stomach that is delivered to the small intestine. The upper part of the duodenum (pars superior) is located under the right liverlobe and is connected to it by the ligamentum hepaduodenale. In addition, this part is in close proximity to the gallbladder. The right kidney and adrenal gland are found close to the adjacent part of the pars descendens.
In the concavity of the loop of the duodenum are the elevations of the papilla duodeni minor and papilla duodeni major with the confluence of the ductus pancreaticus accessorius in the former elevation and the confluence of the ductus choledochus and ductus pancreaticus in the latter. Here, the delivery of bile and pancreas to the food pulp occurs in the uppermost section of the small intestine.
Der untere Teil des Dünndarms, das Ileum mündet im Bereich der Bauhin-Klappe in den Blinddarm (lat. Caecum) und somit in den Dickdarm.
Lage In situ
Der Großteil des Duodenums liegt retroperitoneal während ein kleiner Teil (Pars superior duodeni) intraperitoneal zu finden ist. Durch die Nähe des Caput pancreatis können sich krankhafte Veränderungen der Pankreas (Tumore und Fehlbildungen) negativ auf die natürliche Funktion des obersten Dünndarmabschnittes auswirken.
Der Rest des Dünndarms füllt die Peritonealhöhle gänzlich aus. An einigen Stellen weist er spezifische Engstellen auf, dort kann eine besondere Gefahr von eventuell feststeckenden Festkörpern ausgehen, die dann die Funktion des Darmes massiv stören. Dazu gehören der Übergang von Magenpförtner (lat. Pylorus) zum Duodenum, der Übergang von Duodenum zu Jejunum (sog. Flexura duodenojejunalis) sowie der Übergang von Ileum zum Dickdarm (sog. Ostium ileale).
Erkrankungen
