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The small intestine is a long-narrow tube that is part of the digestive system, found between the stomach and the large intestine. It is the primary site of nutrient absorption, where the majority of the breakdown and absorption of food occurs.
The small intestine is composed of four main layers: the mucosa, submucosa, and muscularis propria, and in the small intestine, the outermost layer is a layer of connective tissue called the serosa. The mucosa is the innermost layer and is composed of three layers: the epithelium, the lamina propria, and the muscularis mucosae.
The epithelium is made up of enterocytes, goblet cells, enteroendocrine cells, and Paneth cells. The submucosa contains blood vessels, lymphatic vessels, and nerves. The muscularis externa consists of smooth muscle cells arranged in an inner circular layer and an outer longitudinal layer. The serosa is a thin layer of loose connective tissue that allows the small intestine to move more freely within the abdomen and contains blood vessels, nerves, and lymphatic vessels as well.
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