Small intestine

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The small intestine is an approximately 6m long organ of the digestive tract and is responsible for the absorption of nutrients. It is divided into three sections: duodenum, jejunum and ileum. Characteristic of its inner surface are the circular folds (of Kerckring), intestinal villi, crypts and microvilli, which significantly increase the resorption surface and optimize nutrient absorption.

The wall of the small intestine consists of the typical layer arrangement of the digestive tract. The mucosa is lined by a single-layered columnar epithelium characterized by enterocytes, goblet cells and enteroendocrine cells. Deep to the mucosa lies the lamina propria with many lymph follicles and the muscularis mucosae. The submucosa contains glands, blood and lymphatic vessels, and the submucosal plexus (of Meissner). The muscular coat consists of an inner circular muscle layer and an outer longitudinal muscle layer, between which the myenteric plexus (of Auerbach) is located. The outer serosa surrounds the small intestine in the peritoneal space.

The three sections of the small intestine can be distinguished from each other with the help of certain characteristics.

• The duodenum contains duodenal submucosal glands (of Brunner) in the submucosa that secrete mucins and bicarbonate.
• In the jejunum, the circular folds (of Kerckring) are most pronounced.
• Typical of the ileum are abundant aggregated lymphoid nodules (Peyer's patches), which are part of the lymphatic tissue of the intestine (GALT) and are collections of lymph follicles. The circular folds are less pronounced here and the villi are also shorter in this region.

Watch the following video to learn more about the histological features of the first section of the small intestine, the duodenum:

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Ready to review all these structures in further detail? Take a look at our image galleries below. 

Lastly, let us review the histological features of the sections of the small intestine. Note: The histological images of the duodenum are that of a duodenal biopsy; hence not all sections of the wall are visible.

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