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Small Intestine

Synonym: Intestinum tenue
German: Dünndarm

1 Definition

Small intestine is defined as the section of the bowel from the pyloric orifice (Pylorus) through to the Bauhin’s valve, which predominately serves the absorption of substances and water taken through the food.

2 Division

The small intestine can be divided into three sections of different lengths:

The duodenum measuring approximately 24 cm is the shortest section. Overall the small intestine in adults has a length of approximately 5-6 metres. It reaches parts of the duodenum intraperitoneal.

3 Anatomy

The small intestine is located in the central section of the abdominal cavity in folded loops and – up to parts of the duodenum – is fixed at the posterior abdominal wall with a mesentery. At 3 sides, it is surrounded by the colon, a part of it intrudes downwards into the area below the apertura pelvis superior pelvic inlet.

3.1 Arterial supply

The small intestine is supplied with arterial blood from the following vessels:

4 Histology

In order to improve the absorption, the small intestine has anatomic and cellular structures, which significantly enlarge the surface. The mucous membrane of the small intestine lines the lumen of the small intestine, therefore not as a smooth surface but is lined wrinkly. The wrinkles reaching up to 1 cm are called circular folds (plicae circulares) or Kerckring folds. However, the mucosa and the submuscosa are involved in its development, but not the tunica muscularis muscular layer.

A typical characteristic of the mucous membrane of the small intestine is its organisation into finger-like or leaf-shaped projections, the intestinal villis (Villi intestinales), and tubular intestinal glands, the crypts (intestinal crypts) – also known as crypts of Lieberkühn.

The actual epithelium of the small intestine comprises of a single-layered columnar epithelium. The cell pole directed at the intestinal lumen delivers a high concentration of microvilli.

5 Physiology

The small intestine serves the digestion and absorption of different food components. The chyme is moved forwarded by the peristaltic movements of the intestinal wall.

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