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Version vom 4. Januar 2022, 15:24 Uhr
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.
The lower part of the small intestine, the ileum opens into the appendix (lat. caecum) in the area of the Bauhin's valve and thus into the colon.
Position In situ
The majority of the duodenum is located retroperitoneally while a small part (pars superior duodeni) is found intraperitoneally. Due to the proximity of the caput pancreatis, pathological changes of the pancreas (tumors and malformations) can have a negative effect on the natural function of the upper small intestinal segment.
The rest of the small intestine completely fills the peritoneal cavity. In some places, it has specific constrictions, where a particular danger can arise from possibly stuck solid bodies, which then massively disrupt the function of the intestine. These include the transition from the pylorus to the duodenum, the transition from the duodenum to the jejunum (flexura duodenojejunalis) and the transition from the ileum to the colon (ostium ileale).
Diseases
